Figure Of Merit For Materials Research Articles

High hole mobility in physical vapour deposition-grown tellurium-based transistors.

Carrier mobility is one of most important figures of merit for materials that can determine to a large extent the corresponding device performances. So far, extensive efforts have been devoted to the mobility improvement of two-dimensional (2D) materials regarded as promising candidates to complement the conventional semiconductors. Graphene has amazing mobility but suffers from zero bandgap. Subsequently, 2D transition-metal dichalcogenides benefit from their sizable bandgap while the mobility is limited. Recently, the 2D elemental materials such as the representative black phosphorus can combine the high mobility with moderate bandgap; however the air-stability is a challenge. Here, we report air-stable tellurium flakes and wires using the facile and scalable physical vapour deposition (PVD) method. The prototype field-effect transistors were fabricated to exhibit high hole mobility up to 1485 cm2 V−1 s−1 at room temperature and 3500 cm2 V−1 s−1 at low temperature (2 K). This work can attract numerous attentions on this new emerging 2D tellurium and open up a new way for exploring high-performance optoelectronics based on the PVD-grown p-type tellurium.

Using Video Photometry to Measure the 3 MeV Proton Half Brightness Fluence for Tetrakis (Dibenzoylmethide) Europium (III) Triethylammonium

In recent years, luminescent materials have been proposed for use as smart sensors to detect structural damage using triboluminescence, measure incident radiation fluence using radioluminescence, and monitor surface temperature using phosphor thermometry. To sense structural damage using triboluminescence, appropriate materials are embedded in a composite host structure for various applications. When the damage occurs in the host structure, it leads to the fracture of the triboluminescent crystals resulting in light emission. This process provides a real-time warning that structural damage has occurred. The TL emission of the candidate material has to be sufficiently bright, so that the light signal reaching from the point of fracture to the detector, through a fiber optics cable, is strong enough to be detected. The majority of the known triboluminescent materials do not emit light with sufficient intensity to allow detection with compact and inexpensive detectors. Over the past forty years, some materials have been reported with TL of sufficient intensity for the light emission to be easily observed with the naked eye. Out of these triboluminescent materials, only few could satisfy the above criterion. Tetrakis (Dibenzoylmethide) Europium (III) Triethylammonium (EuD4TEA), one of the brightest known TL materials and is a potential candidate for application to this type of hybrid smart sensor in extreme environments. Recent measurements by the authors indicate that the decay time for EuD4TEA is bi-exponential and can be used to measure temperatures from -10 to 80 °C. Ionizing radiation in space poses a significant challenge to future human and robotic exploration missions. Any intelligent sensor material used in space must also be resistant to ionizing radiation. Sources and types of such radiation include galactic and solar electrons and protons, x-rays, ultraviolet light, and magnetically trapped charged particles in radiation belts. While much research has been devoted to characterizing material degradation due to electron exposure, surprisingly little work seems to have been done on proton damage. Research has shown that proton bombardment in the keV to MeV range, like that occurring in space, reduces the intensity of fluorescence. Thus, proton irradiation will likely reduce the ability of a candidate smart material to emit fluorescence.Practical space-based sensors based on luminescence will depend heavily upon research investigating the resistance of these materials to ionizing radiation and the ability to anneal or self-heal from damage caused by such radiation. In 1951, Birks and Black showed experimentally that the fluorescence efficiency of anthracene bombarded by alphas varies with total fluence (N) as (I/I0) = 1/(1 + AN), where I is the luminescence yield, I0 is the initial luminescence yield, and A is a constant. The half brightness fluence (N1/2) is a material figure of merit and is defined as the reciprocal of A. Broser and Kallmann developed a similar relationship to the Birks and Black equation for inorganic phosphors irradiated using alpha particles. From 1990 to the present, we have found that the Birks and Black relation describes the reduction in emission yield for every tested luminescent material except lead phosphate glass due to proton irradiation.These results indicate that radiation produced quenching centers compete with emission centers for absorbed energy. In 2016, the N1/2 for EuD4TEA irradiated with 3 MeV protons was measured to be about 3 x 1010 mm-2. Conversely, ZnS:Mn compounds tested were found to have N1/2 values for 3 MeV protons that are nearly one thousand times larger (~1013 mm-2). According to Tribble, a spacecraft at 1 AU from the Sun will receive a 1 MeV proton fluence of less than 1011 mm-2 from a large solar event. Likewise, 1 MeV proton fluences in the Earth’s radiation belts and the Earth-Moon-Sun Lagrange points will be even less than the 1011 mm-2 value from large solar events. For this reason, EuD4TEA might be a candidate sensor material to monitor large-scale solar events for astronauts in vehicles flying in near earth space. Since their N1/2 values are larger, ZnS:Mn compounds are more suited for use as sensors in higher radiation environments or for very long duration space missions. The purpose of this presentation is to present preliminary results from a 1U CubeSat payload using a EuD4TEA-based sensor to measure ionizing radiation in Earth orbit. This flight experiment is a natural outgrowth of earlier ground-based radiation exposure measurements that will be used to determine if EuD4TEA-based materials can be used as a real-time sensor for applications in space.

Using Exotic Materials like EuD4TEA to Monitor Damage and Radiation Exposure in Extreme Environments

In recent years, luminescent materials have been proposed for use as smart sensors to measure structural damage and to monitor radiation fluence. To sense structural damage using triboluminescence, appropriate materials are embedded in a composite host structure for various applications, such as crew launch or exploration vehicles. When the damage occurs in the host structure, it leads to the fracture of the triboluminescent crystals resulting in light emission. This process provides a real-time warning that structural damage has occurred. The TL emission of the candidate material has to be sufficiently bright, so that the light signal reaching from the point of fracture to the detector, through a fiber optics cable, is strong enough to be detected. The majority of the known triboluminescent materials do not emit light with sufficient intensity to allow detection with compact and inexpensive detectors. Over the past 40 years, some materials have been reported with TL of sufficient intensity for the light emission to be easily observed with the naked eye. Out of these triboluminescent materials, only few could satisfy the above criterion. Europium tetrakis dibenzoylmethide triethylammonium (EuD4TEA), one of the brightest known TL materials and is a potential candidate for application to this type of hybrid smart sensor in extreme environments. Ionizing radiation in the extreme environment of space poses a significant challenge to future human and robotic exploration missions. To be used in space, any intelligent sensor material must also be resistant to ionizing radiation. Sources and types of such radiation include galactic and solar electrons and protons, x-rays, ultraviolet light, and magnetically trapped charged particles in radiation belts. While much research has been devoted to characterizing material degradation due to electron exposure, surprisingly little work seems to have been done on proton damage. Research has shown that proton bombardment in the keV to MeV range, like that occurring in space, reduces the intensity of fluorescence. Thus, proton irradiation will likely reduce the ability of a candidate smart material to emit fluorescence. Practical space-based sensors based on luminescence will depend heavily upon research investigating the resistance of these materials to ionizing radiation and the ability to anneal or self-heal from damage caused by such radiation. In 1951, Birks and Black showed experimentally that the fluorescence efficiency of anthracene bombarded by alphas varies with total fluence (N) as (I/I0) = 1/(1 + AN), where I is the luminescence yield, I0 is the initial luminescence yield, and A is a constant. The half brightness fluence (N1/2) is a material figure of merit and is defined as the reciprocal of A. Broser and Kallmann developed a similar relationship to the Birks and Black equation for inorganic phosphors irradiated using alpha particles. From 1990 to the present, we have found that the Birks and Black relation describes the reduction in emission yield for every tested luminescent material except lead phosphate glass due to proton irradiation. These results indicate that radiation produced quenching centers compete with emission centers for absorbed energy. Recently, the N1/2 for EuD4TEA irradiated with 3 MeV protons was measured to be about 3 x 1010 mm-2. Conversely, ZnS:Mn compounds tested were found to have N1/2 values for 3 MeV protons that are nearly one thousand times larger (~1013 mm-2). According to Tribble, a spacecraft at 1 AU from the Sun will receive a 1 MeV proton fluence of less than 1011 mm-2 from a large solar event. Likewise, 1 MeV proton fluences in the Earth’s radiation belts and the Earth-Moon-Sun Lagrange points will be even less than the 1011 mm-2 value from large solar events. For this reason, EuD4TEA might be a candidate sensor material to monitor large-scale solar events for astronauts in vehicles flying in near earth space. Since their N1/2 values are larger, ZnS:Mn compounds are more suited for use as sensors in higher radiation environments or for very long duration space missions. The purpose of this presentation is to present results from all research completed in this area. Particular emphasis will be placed on synthesizing EuD4TEA material as well as the design and construction of a 1U CubeSat payload that will orbit the Earth carrying an innovative first generation sensor to monitor radiation fluence. This flight experiment is a natural outgrowth of earlier ground based radiation exposure measurements that will be used to determine if EuD4TEA-based materials can be used as a real-time structural damage and/or radiation sensor for applications in space or other extreme environments.

Analysis and experimental validation of the figure of merit for piezoelectric energy harvesters

We demonstrate that the figure of merit for materials in piezoelectric energy harvesters does not depend on the compliance.

Potential of Using EuD4tea for Space-Based Damage and Radiation Sensors

In recent years, luminescent materials have been proposed as active elements for smart sensors to measure structural damage using triboluminescence (TL) and to monitor radiation fluence. To sense structural damage, these materials are embedded in a composite host structure for various applications, such as crew launch or exploration vehicles. When the damage/fracture occurs in the host composite structure, it will lead to the fracture of the TL crystals resulting in light emission. This will provide a warning, in real time, that structural damage has occurred. The TL emission of the candidate material has to be sufficiently bright, so that the light signal reaching from the point of fracture to the detector, through a fiber optics cable, is strong enough to be detected. The majority of the known TL materials do not emit light with sufficient intensity to allow detection with compact and inexpensive detectors. Over the past 40 years, some materials have been reported that TL with sufficient intensity for the light emission to be easily observed with the naked eye. Out of these TL materials, only few could satisfy the above criterion. Europium tetrakis dibenzoylmethide triethylammonium (EuD4TEA), one of the brightest known TL materials and is a potential candidate for application to this type of hybrid smart sensor. Space radiation poses a significant challenge to human and robotic exploration missions to deep space. To be used in space, any intelligent sensor material must also be resistant to ionizing radiation. Sources and types of such radiation include galactic and solar electrons and protons, x-rays, ultraviolet light, and magnetically trapped charged particles in radiation belts. While much research has been devoted to characterizing material degradation due to electron exposure, surprisingly little work seems to have been done on proton damage. Research has shown that proton bombardment in the keV to MeV range, like that occurring in space, reduces the intensity of fluorescence. Thus, proton irradiation will likely reduce the ability of a candidate smart material to emit fluorescence. Practical space-based sensors based on luminescence will depend heavily upon research investigating the resistance of these materials to ionizing radiation and the ability to anneal or self-heal from damage caused by such radiation. In 1951, Birks and Black showed experimentally that the fluorescence efficiency of anthracene bombarded by alphas varies with total fluence (N) as (I/I0) = 1/(1 + AN), where I is the luminescence yield, I0 is the initial luminescence yield, and A is a constant. The half brightness fluence (N1/2) is a material figure of merit and is defined as the reciprocal of A. Broser and Kallmann developed a similar relationship to the Birks and Black equation for inorganic phosphors irradiated using alpha particles. From 1990 to the present, we have found that the Birks and Black relation describes the reduction in emission yield for every tested luminescent material except lead phosphate glass due to proton irradiation. These results indicate that radiation produced quenching centers compete with emission centers for absorbed energy. Recently, we measured the N1/2 for EuD4TEA irradiated with 3 MeV protons to be about 3 x 1010 mm-2. Conversely, ZnS:Mn compounds tested were found to have N1/2 values for 3 MeV protons that are nearly one thousand times larger (~1013 mm-2). According to Tribble, a spacecraft at 1 AU from the Sun will receive a 1 MeV proton fluence of less than 1011 mm-2 from a large solar event. Likewise, 1 MeV proton fluences in the Earth’s radiation belts and the Earth-Moon-Sun Lagrange points will be even less than the 1011 mm-2 value from large solar events. For this reason, EuD4TEA might be a candidate sensor material to monitor large-scale solar events for astronauts in vehicles flying in near earth space. Since their N1/2 values are larger, ZnS:Mn compounds are more suited for use as sensors in higher radiation environments or for very long duration space missions. Late this year, a 1U CubeSat payload will be placed in Earth orbit carrying an innovative first generation EuD4TEA sensor that will be used to monitor radiation fluence. This flight experiment is a natural outgrowth of earlier ground based radiation exposure measurements. The purpose of this presentation is to present results from research completed in this area from 1990 to present. Particular emphasis will be placed on recent TL and radiation exposure measurements using EuD4TEA. This groundbreaking research can be used to help determine if EuD4TEA-based materials can be used as a real-time structural damage and/or radiation sensor for space applications.

Electroelastodynamics of flexoelectric energy conversion and harvesting in elastic dielectrics

Flexoelectricity is the generation of electric polarization by the application of a non-uniform mechanical strain field, i.e., a strain gradient. This phenomenon is exhibited by all elastic dielectrics, but is expected to be significant only at very small scales. Energy harvesting is a potential future application area of flexoelectricity to enable next-generation ultra-low-power MEMS/NEMS devices by converting ambient vibrations into electricity. In this paper, an electroelastodynamic framework is presented and analyzed for flexoelectric energy harvesting from strain gradient fluctuations in centrosymmetric dielectrics, by accounting for the presence of a finite electrical load across the surface electrodes as well as two-way electromechanical coupling, and capturing the size effect. The flexoelectric energy harvester model is based on the Euler-Bernoulli beam theory and it assumes the main source of polarization to be static bulk flexoelectricity. Following recent efforts on the converse flexoelectric effect in finite samples, the proposed model properly accounts for thermodynamically consistent, symmetric direct and converse coupling terms. The transverse mode flexoelectric coupling coefficient (k) is obtained analytically as a direct measure of energy conversion; its dependence on the cantilever thickness and a material Figure of Merit (FoM) is shown. Size effects are further demonstrated by simulations of the electromechanical frequency response for a Strontium Titanate (STO) energy harvester at different geometric scales. It is obtained that the flexoelectric coupling coefficient of an STO cantilever for the fundamental bending mode increases from k≈3.5×10−7 to k≈0.33 as the thickness is reduced from mm- to nm-level. A critique of the experimentally identified large flexoelectric coefficient for Barium Strontium Titanate (BST) from the literature is also given with a coupling coefficient perspective.

Standards and figure-of-merits for quantifying the performance of triboelectric nanogenerators.

Triboelectric nanogenerators have been invented as a highly efficient, cost-effective and easy scalable energy-harvesting technology for converting ambient mechanical energy into electricity. Four basic working modes have been demonstrated, each of which has different designs to accommodate the corresponding mechanical triggering conditions. A common standard is thus required to quantify the performance of the triboelectric nanogenerators so that their outputs can be compared and evaluated. Here we report figure-of-merits for defining the performance of a triboelectric nanogenerator, which is composed of a structural figure-of-merit related to the structure and a material figure of merit that is the square of the surface charge density. The structural figure-of-merit is derived and simulated to compare the triboelectric nanogenerators with different configurations. A standard method is introduced to quantify the material figure-of-merit for a general surface. This study is likely to establish the standards for developing TENGs towards practical applications and industrialization.

Impact of nonlinear loss on stimulated Brillouin scattering

We study the impact of two-photon absorption (2PA) and fifth-order nonlinear loss such as 2PA-induced free-carrier absorption in semiconductors on the performance of Stimulated Brillouin Scattering devices. We formulate the equations of motion including effective loss coefficients, whose explicit expressions are provided for numerical evaluation in any waveguide geometry. We find that 2PA results in a monotonic, algebraic relationship between amplification, waveguide length and pump power, whereas fifth-order losses lead to a non-monotonic relationship. We define a figure of merit for materials and waveguide designs in the presence of fifth-order losses. From this, we determine the optimal waveguide length for the case of 2PA alone and upper bounds for the total Stokes amplification for the case of 2PA as well as fifth-order losses. The analysis is performed analytically using a small-signal approximation and is compared to numerical solutions of the full nonlinear modal equations.

Fuel Cycle System Analysis Implications of Sodium-Cooled Metal-Fueled Fast Reactor Transuranic Conversion Ratio

If advanced fuel cycles are to include a large number of fast reactors (FRs), what should be the transuranic (TRU) conversion ratio (CR)? The nuclear energy era started with the assumption that they should be breeder reactors (CR > 1), but the full range of possible CRs eventually received attention. For example, during the recent U.S. Global Nuclear Energy Partnership program, the proposal was burner reactors (CR < 1). Yet, more recently, Massachusetts Institute of Technology’s “Future of the Nuclear Fuel Cycle” proposed CR [approximately] 1. Meanwhile, the French company EDF remains focused on breeders. At least one of the reasons for the differences of approach is different fuel cycle objectives. To clarify matters, this paper analyzes the impact of TRU CR on many parameters relevant to fuel cycle systems and therefore spans a broad range of topic areas.The analyses are based on a FR physics parameter scan of TRU CR from 0 to [approximately]1.8 in a sodium-cooled metal-fueled FR (SMFR), in which the fuel from uranium-oxide-fueled light water reactors (LWRs) is recycled directly to FRs and FRs displace LWRs in the fleet. In this instance, the FRs are sodium cooled and metal fueled. Generally, it is assumed that all TRU elements are recycled, which maximizes uranium ore utilization for a given TRU CR and waste radiotoxicity reduction and is consistent with the assumption of used metal fuel separated by electrochemical means. In these analyses, the fuel burnup was constrained by imposing a neutron fluence limit to fuel cladding to the same constant value. This paper first presents static, time-independent measures of performance for the LWR [right arrow] FR fuel cycle, including mass, heat, gamma emission, radiotoxicity, and the two figures of merit for materials for weapon attractiveness developed by C. Bathke et al.No new fuel cycle will achieve a static equilibrium in the foreseeable future. Therefore, additional analyses are shown with dynamic, time-dependent measures of performance including uranium usage, TRU inventory, and radiotoxicity to evaluate the complex impacts of transition from the current uranium-fueled LWR system, and other more realistic impacts that may not be intuited from the time-independent steady-state conditions of the end-state fuel cycle. These analyses were performed using the Verifiable Fuel Cycle Simulation Model VISION.Compared with static calculations, dynamic results paint a different picture of option space and the urgency of starting a FR fleet. For example, in a static analysis, there is a sharp increase in uranium utilization as CR exceeds 1.0 (burner versus breeder). However, in dynamic analyses that examine uranium use over the next 1 to 2 centuries, behavior as CR crosses the 1.0 threshold is smooth, and other parameters such as the time required outside of reactors to recycle fuel become important.Overall, we find that there is no unambiguously superior value of TRU CR; preferences depend on the relative importance of different fuel cycle system objectives.

Substituent effects in a series of 1,7-C60(RF)2 compounds (RF = CF3, C2F5, n-C3F7, i-C3F7, n-C4F9, s-C4F9, n-C8F17): electron affinities, reduction potentials and E(LUMO) values are not always correlated

A series of seven structurally-similar compounds with different pairs of RF groups were prepared, characterized spectroscopically, and studied by electrochemical methods (cyclic and square-wave voltammetry), low-temperature anion photoelectron spectroscopy, and DFT calculations (five of the compounds are reported here for the first time). This is the first time that a set of seven RF groups have been compared with respect to their relative effects on E1/2(0/−), electron affinity (EA), and the DFT-calculated LUMO energy. The compounds, 1,7-C60(RF)2 (RF = CF3, C2F5, i-C3F7, n-C3F7, s-C4F9, n-C4F9 and n-C8F21), were found to have statistically different electron affinities (EA), at the ±10 meV level of uncertainty, but virtually identical first reduction potentials, at the ±10 mV level of uncertainty. The lack of a correlation between EA and E1/2(0/−), and between E(LUMO) and E1/2(0/−), for such similar compounds is unprecedented and suggests that explanations for differences in figures of merit for materials and/or devices that are based on equating easily measurable E1/2(0/−) values with EAs or E(LUMO) values should be viewed with caution. The solubilities of the seven compounds in toluene varied by nearly a factor of six, but in an unpredictable way, with the C2F5 and s-C4F9 compounds being the most soluble and the i-C3F7 compound being the least soluble. The effects of the different RF groups on EAs, E(LUMO) values, and solubilities should help fluorine chemists choose the right RF group to design new materials with improved morphological, electronic, optical, and/or magnetic properties.

8MeV electron irradiation effect on the dielectric and optical properties of iminodiacetic acid doped ferroelectric triglycine sulphate crystals

Abstract Single crystal of iminodiacetic acid (5 mol%) doped Tri Glycine Sulphate (IDATGS) was grown by slow evaporation from its aqueous solution at constant temperature, using solution growth method. The dielectric constant ( e ′) and pyroelectric current ( I P ) were measured over the temperature range of 30–60 °C in the ferroelectric direction. The measured values of e ′ and I P were found to be smaller compared to pure triglycine sulphate (TGS) crystal parameters. But increased transition temperature was observed for doped crystals. Curie Weiss constants C P and C f in the paraelectric and ferroelectric phases were also determined. The doped crystal was irradiated with graded dosages from 5 to 80 kGy of electron beam from 8 MeV Microtron at room temperature and radiation effects on optical and dielectric properties were studied. The UV–Vis absorption spectrum indicates that the UV lower cutoff shifts towards the higher wavelength region (red shift) and the optical band gap is found to be decreasing with the increase of electron dose. It is also observed that the electron irradiation effects in pure and doped TGS were found to be long lasting. The dielectric study shows that there is a gradual reduction in dielectric constant at T C and shifting of Curie temperature towards lower temperature region with the increase in electron radiation dose. The material figures of merit were found increased after the crystal was irradiated. Induced changes in the physical and optical properties due to irradiation may help one to tailor the device quality and characteristics.

Shear stress in magnetorheological finishing for glasses

We report in situ, simultaneous measurements of both drag and normal forces in magnetorheological finishing (MRF) for what is believed to be the first time, using a spot taking machine (STM) as a test bed to take MRF spots on stationary parts. The measurements are carried out over the entire area where material is being removed, i.e., the projected area of the MRF removal function/spot on the part surface, using a dual force sensor. This approach experimentally addresses the mechanisms governing material removal in MRF for optical glasses in terms of the hydrodynamic pressure and shear stress, applied by the hydrodynamic flow of magnetorheological fluid at the gap between the part surface and the STM wheel. This work demonstrates that the volumetric removal rate shows a positive linear dependence on shear stress. Shear stress exhibits a positive linear dependence on a material figure of merit that depends upon Young's modulus, fracture toughness, and hardness. A modified Preston's equation is proposed that better estimates MRF material removal rate for optical glasses by incorporating mechanical properties, shear stress, and velocity.

RELATION OF INTER-ATOMIC FORCES IN SOLIDS TO BULK MODULUS, COHESIVE ENERGY AND THERMAL EXPANSION

We present theoretical expressions relating the cohesive energy to the bulk modulus, the force constant and the lattice constant applicable to solids with a variety of crystal structures. We have found that the cohesive energy is directly proportional to the ratio between the product of the bulk modulus through the atomic volume and the exponent of the repulsion term. We have defined a figure of merit for materials as the ratio between the product of the bulk modulus through the atomic volume and the cohesive energy. The reciprocal of this ratio is a measure of the hardness of materials. Likewise, we have found the expressions for anharmonicity and thermal expansion coefficients, which can explain, also, their possible negative values.

English

Pyroelectric sensors based on ceramic materials have found applications in IR detection in defence and civil systems. To develop suitable ceramic material for IR detector applications, a modified PZT system with compositional formula Pb 1-x Sm x (Zr 0.58 Fe 0.18 Mn 0.02 Nb 0.2 Ti 0.02 )O 3 where 0 ≤ x ≤ 0.025 was synthesised by conventional solid state reaction method. The materials were characterised for their properties like dielectric and pyroelectric coefficient. Hysteresis loop was recorded at room temperature. The sample with 2 mole per cent samarium (Sm) substitutions was found to be more promising for sensor application based on its high material's figure of merit (FOM). Sensors fabricated with this material were integrated with FET amplifier. The devices configured with compensating element were evaluated for different chopping frequencies. The value of material's FOM, F D , and detectivity, D*, were determined from measured parameters and were, 3.6 x 10 -5 Pa -1/2 and 2 x 10 8 cmHz 1/2 /W, respectively.

Studies on DTGS:PVDF Composites for Pyroelectric Infrared Detectors

The search for new materials for pyroelectric infrared sensors and ultrasonic transducers has led to the design of ferroelectric composites [1–4]. Recent studies on pyroelectric-polymer composites do show their usefulness in large area, light weight, high strength and flexible infrared sensing devices [2, 3]. Among available materials, deuterated triglycine sulfate (DTGS) shows highest pyroelectric performance [5]. The current work describes the fabrication of DTGS:PVDF composites with varying DTGS particle size powders and composition embedded in poly-vinylidene fluoride (PVDF) matrix which is also an important pyroelectric polymer. In this communication we report the results of investigation of the dielectric and pyroelectric properties of new composites. Using these properties, applicable materials figures of merit are calculated for their use in infrared detecting devices, and are also compared with investigated pyroelectric composites. The results are encouraging for their use as infrared sensors.

Improvement in material figure of merit of PLZT by samarium substitution

The paper reports dielectric and pyroelectric properties of samarium substituted PLZT. The polycrystalline samples with chemical formula Pb0.925-xSmxLa0.075(Zr0.2Ti0.8)0.981O3 with x varying from 0 to 0.02 were prepared by conventional dry ceramic method. XRD analysis shows all the compositions to be single phase with tetragonal structure. Room temperature dielectric constant increases marginally with x while dielectric loss is found to decrease appreciably. Pyroelectric coefficient improves with x. The sample with x = 0.015 exhibited the maximum value of material figure of merit in this series of compositions.

Dielectric and pyroelectric properties of samarium modified lead titanate

The paper reports the influence of samarium substitution on the dielectric and pyroelectric properties of modified lead titanate. Polycrystalline samples with compositional formula Pb1-xSmxTi0.98Mn0.02O3, with × varying from 0 to 0.15, were synthesized by solid state reaction technique. XRD analysis shows all the samples to be single phase with tetragonal structure. Tetragonality (c/a) value decreases with increasing samarium substitution level x. Room temperature value of dielectric constant was observed to increase with increasing x. Dielectric loss (tanδ) initially increases up to × = 0.1 and then starts decreasing. Curie temperature was found to decrease with x. Pyroelectric coefficient and material figure of merit (FD) increases with x. The composition with x=0.15 gives highest value of FD and is suitable for IR sensor application.

Materials Issues in the Application of Ferromagnetic Films in Tunable High Q VHF/UHF Devices

AbstractThin ferromagnetic films have narrow ferromagnetic resonance bandwidths, and large RF permeabilities that are attractive for tunable high Q device applications. They can also be processed at low temperatures and integrated with most RF and microwave materials. At VHF/UHF frequencies, where discrete devices can be realized, magnetic loss tangents (Q−1) less than 10−3 can be obtained, if the effects of spin resonance and eddy current losses are reduced. The material figure of merit requires a tradeoff of the permeability, and Q. The highest FOM is obtained by maximizing the magnetization, anisotropy, resistivity, and minimizing the magnetic loss. This paper discusses the interplay of these properties, and the fill factor and magnetic bias required for tunable inductors with Q&gt;1000 in the ∼50-500 MHz range. The most promising candidates for these applications are shown to be reactively sputtered nanocrystalline films. The large resistivity, magnetization, and thickness of these films can be used to attain large film permeances, and increased shape anisotropy fields from patterned film objects. The latter eliminates the need for using a large bias magnet to achieve Q's ∼1000 at VHF/UHF operating frequencies.

INFLUENCE OF MICROSTRUCTURE ON ULTRASONIC BACKSCATTERING NOISE IN TITANIUM ALLOYS

Abstract Backscattering from microstructural discontinuities such as grain boundaries in metals produces noise which is observed in most ultrasonic experiments. These signals provide information concerning the microstructure of the material. The utilization of the absolute values of the noise signals in materials characterization is described in this paper. A quantitative model for the dependence of the noise signals upon the radiation pattern of the transducer is presented, including such measurement variables as transducer radius, frequency and ultrasonic propagation paths. The microstructure enters into the problem via a scattering parameter, or material figure of merit (FOM) for grain noise severity. For a simple case such as a single phase polycrystal, this may be thought of as the root mean square value of the scattering amplitude of a grain embedded in an effective medium representing the polycrystal. After reviewing this model, the paper will concentrate on experimental tests of its accuracy. Incl...

Modeling of longitudinally pumped CW Ti:sapphire laser oscillators

Longitudinal pumping of CW Ti:sapphire oscillators is considered to predict the power output of such oscillators using folded, astigmatically compensated cavities. The model predicts how the oscillator performance is affected by the selection of Ti/sup 3+/ concentration, material figure of merit, rod length, and pump and cavity mode waists. Experimental results for broadband CW oscillators pumped by CW argon ion lasers are reported, and these are shown to be in excellent agreement with theory. Nearly 30% slope efficiency is achieved with a four-mirror folded cavity and even higher efficiencies are predicted for optimized pumping.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>