Room Temperature For Samples Research Articles

ZnO/Organic superlattice with phase composite structure for enhanced thermoelectric performance at low temperature

Semiconducting metal oxides, such as zinc oxide (ZnO), are gaining recognition for thermoelectric applications due to their temperature stability, availability, eco-friendliness, and cost-effectiveness. However, ZnO faces challenges in achieving high ZT value due to its low carrier concentration and high thermal conductivity. Traditional methods, like doping and defect engineering, have shown limited success in overcoming these challenges. In this study, we introduce a unique superlattice structure with a phase-composite composition that significantly decreases thermal conductivity through enhanced phonon scattering while maintaining the power factor by inducing new resonant conducting states near the mobility edge. By optimizing nanolayer thickness and doping concentration, we achieved a remarkable power factor of 14.6 μW cm−1 K−2 and reduced thermal conductivity to ∼1.97 W m−1 K−1 at room temperature in samples with 6 nm-thick ZnO nanolayers fabricated at 100 °C. This leads to a ZT value of ∼0.22 at 300 K, the highest among metal oxide thermoelectric materials at low temperatures, which further increases to ∼0.55 at 510 K. These findings demonstrate the potential of hybrid superlattices for efficient low-temperature thermoelectric applications.

Magnetic, DC Electrical, and Impedance Properties of Zn Doped Yttrium Iron Garnet Nanoparticles

Y3Fe5-xZnxO12 with x = 0; 0.02; 0.04; 0.06; 0.08; 0.1 (YIG) particle materials were fabricated by sol-gel method combined with heat treatment at 900 °C and 1,000 °C with different annealing times (2 h and 5 h) and heating rates (5 °C/min and 2 °C/min). X-ray diffraction patterns show that the obtained samples are single crystalline phases at the condition of an annealing temperature of 900 °C for 5 h and a heating rate of 2 degrees/min. FESEM images of the samples show particle sizes from the submicron to the micrometer. The magnetization of the samples decreases as the doping concentration increases. I-V characteristics and complex impedance spectra at room temperature of samples were measured. The results show that the resistivity value of the doped samples decreases in the range of 5-6 orders in magnitude compared with that of the pure YIG sample. The contribution of the grain boundaries to the impedance was analyzed. The conducting process is explained due to the tunneling of charge carriers across the grain boundary.

Refractive index dispersion of BGa(As)P alloys in the near-infrared for III-V laser integration on silicon

BxGa(1−x)P and BxGa(1−x)AsyP(1−y) alloys are of potential interest in III-V heterostructures for integration with silicon. Waveguide design utilizing these alloys requires an understanding of the refractive index properties and their variation with composition. Refractive index dispersion was measured and modeled in the wavelength range of 827–2254 nm using spectroscopic ellipsometry at room temperature for samples with boron and arsenic fractions from 0% to 6.6% and 0% to 17%, respectively. The refractive index was found to increase with increasing boron composition as a result of strain due to lattice constant mismatch with the silicon substrate. For the arsenic-containing alloy, the refractive index was found to increase independently of strain. An empirical model based on the composition dependent variation of Cauchy dispersion function coefficients was developed for BGaAsP alloys lattice matched to silicon at the growth temperature. This model can be used to calculate the wavelength dependent refractive index of lattice matched boron and arsenic combinations for applications in semiconductor waveguides, an example of which is proposed. The results of this study are of interest more broadly for other III-V on silicon applications including photovoltaics and more generally in terms of the ellipsometric investigations of thin films on non-native substrates.

Effect of Zn nonmagnetic element doping and a polyvinyl pyrrolidone shell layer on the superparamagnetism and stability properties of magnetic nanoparticles

Zn x Fe1−x Fe2O4 nanoparticles (x = 0.0–0.25) were synthesized by the coprecipitation method. Their microstructure was investigated by X-ray diffraction with Rietveld refinement software, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and Fourier transform infrared absorption spectroscopy. Their thermal, magnetic properties were investigated by thermogravimetric analysis and vibrating-sample magnetometer. The nanoparticles exhibited superparamagnetic properties, with a maximum saturation magnetization of 80.2 emu g−1 in H = 11 000 Oe at room temperature for sample with x = 0.20. The Zn nonmagnetic element content is related to the cation distribution in the superlattices and magnetic moment of the particles. The Zn0.15Fe0.85Fe2O4 nanoparticles were coated with polyvinyl pyrrolidone (PVP) with different PVP mass. Their core–shell structure was investigated, the results showed that their chemical stability and saturation magnetization were greater than those of pure Fe3O4. PVP has biological compatibility; thus, Fe0.85Zn0.15Fe2O4/PVP0.75 nanocomposite has the potential to be widely used in medical biology, science and technology.

Single pulse all-optical toggle switching of magnetization without gadolinium in the ferrimagnet Mn2RuxGa

Energy-efficient control of magnetization without the help of a magnetic field is a key goal of spintronics. Purely heat-induced single-pulse all-optical toggle switching has been demonstrated, but so far only in Gd-based amorphous ferrimagnet films. In this work, we demonstrate toggle switching in films of the half-metallic ferrimagnetic Heusler alloys Mn2RuxGa, which have two crystallographically-inequivalent Mn sublattices. Moreover, we observe the switching at room temperature in samples that are immune to external magnetic fields in excess of 1 T, provided they exhibit a compensation point above room temperature. Observation of the effect in compensated ferrimagnets without Gd challenges our understanding of all-optical switching. The dynamic behavior indicates that Mn2RuxGa switches in 2 ps or less. Our findings widen the basis for fast optical switching of magnetization and break new ground for engineered materials that can be used for nonvolatile ultrafast switches using ultrashort pulses of light.

Electroforming-free resistive switching in yttrium manganite thin films by cationic substitution

We report unipolar resistive switching in polycrystalline, hexagonal yttrium manganite thin films grown on unpatterned Pt metal coated SiO2/Si substrates with circular Al top electrodes. Electroforming-free or electroforming-based resistive switching is observed, depending on the chemical composition (Y1Mn1O3, Y0.95Mn1.05O3, Y1Mn0.99Ti0.01O3, and Y0.94Mn1.05Ti0.01O3). The number of loading cycles measured at room temperature for samples with Y1Mn1O3 and Y0.95Mn1.05O3 composition is larger than 103. The dominant conduction mechanism of the metal–insulator–metal structures between 295 K and 373 K in the high resistance state is space charge limited conduction and in the low resistance state is ohmic conduction. Activation energies in Ohm's law region in the high resistance state are calculated from the Arrhenius equation and are evaluated to be 0.39 ± 0.01 eV (Y1Mn1O3), 0.43 ± 0.01 eV (Y0.95Mn1.05O3), 0.34 ± 0.01 eV (Y1Mn0.99Ti0.01O3), and 0.38 ± 0.02 eV (Y0.94Mn1.05Ti0.01O3).

Perovskite-type compounds in anion-substituted LiSr1−0.5xTiTaO6−xFx electrolyte for improving lithium-ion conduction

All-solid-state lithium (Li) ion batteries are regarded as optimal solutions to secure energy problems because of their characteristics, such as no leakage and nonflammability. However, low Li-ion conductivity in these batteries limits their applications. Perovskite-type Li-ion conductors have been considered promising solid electrolytes by replacing A- and B-site ions to improve ion conductivity. In this study, the strategy of replacing O2- anions with F- in perovskite-type structure LiSr1−0.5xTiTaO6−xFx was carried out. Solid electrolytes were successfully prepared by conventional solid-state reactions. The influence of fluorine ion (F-) content in these compounds was systematically investigated regarding ion conductivity. Total conductivity attained was as high as 3.67 × 10−4 S·cm−1 at room temperature in samples with x = 0.1. However, excessive F- doping causes octahedral distortions and produced narrow bottlenecks surrounded by [TiO6] octahedra, which led to decreased conductivity and increased migration activation energy.

Structural and magnetic properties of BiFeO3-PbTiO3 polycrystals

In this manuscript, microstructural, structural and magnetic properties of pure and La doped (0.6)BiFeO3-(0.4)PbTiO3 polycrystals were investigated. X-ray diffraction, transmission and scanning electron microscopy results reveal morphologically uniform particles of rhombohedral and rhombohedral/tetragonal symmetries for pure and La doped samples. An enhanced magnetization, characterized by slim loop hysteretic curves of null remnant magnetization and 2 emu/g saturation (15 kOe) magnetization, is observed at room temperature for samples with average particle size close to 5 nm.

Effect of MgO on thermal shock resistance of CaZrO3 ceramic

In order to improve the thermal shock resistance of CaZrO3, CaZrO3 was synthesized by a solid-state reaction method with analytical ZrO2 and CaCO3 as raw materials, and MgO as additive. The effects of MgO on Flexural strength at room temperature, thermal shock resistance, XRD and microstructure of CaZrO3 were characterized. The results show that the grain growth of CaZrO3 is inhibited and the thermal shock resistance of CaZrO3 is improved by adding MgO. With the increasing of MgO, the flexural strength at room temperature of samples are improved due to the grain refinement. When the addition of MgO is 8%, the flexural strength at room temperature increases to 270.15 MPa. The thermal shock resistance of samples are improved by MgO deflecting and bridging cracks. When the addition of MgO is 4%, the residual flexural strength of samples is the maximum (26.94 MPa).

Electrical study on Carboxymethyl Cellulose-Polyvinyl alcohol based bio-polymer blend electrolytes

The present work deals with the formulation of bio-materials namely carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA) for bio-polymer blend electrolytes (BBEs) system which was successfully carried out with different ratio of polymer blend. The biopolymer blend was prepared via economical & classical technique that is solution casting technique and was characterized by using impedance spectroscopy (EIS). The ionic conductivity was achieved to optimum value 9.12 x 10-6 S/cm at room temperature for sample containing ratio 80:20 of CMC:PVA. The highest conducting sample was found to obey the Arrhenius behaviour with a function of temperature. The electrical properties were analyzed using complex permittivity ε* and complex electrical modulus M* for BBEs system and it shows the non-Debye characteristics where no single relaxation time has observed.

Defect properties of InGaAsN layers grown as sub-monolayer digital alloys by molecular beam epitaxy

The defect properties of InGaAsN dilute nitrides grown as sub-monolayer digital alloys (SDAs) by molecular beam epitaxy for photovoltaic application were studied by space charge capacitance spectroscopy. Alloys of i-InGaAsN (Eg = 1.03 eV) were lattice-matched grown on GaAs wafers as a superlattice of InAs/GaAsN with one monolayer of InAs (<0.5 nm) between wide GaAsN (7–12 nm) layers as active layers in single-junction solar cells. Low p-type background doping was demonstrated at room temperature in samples with InGaAsN layers 900 nm and 1200 nm thick (less 1 × 1015 cm−3). According to admittance spectroscopy and deep-level transient spectroscopy measurements, the SDA approach leads to defect-free growth up to a thickness of 900 nm. An increase in thickness to 1200 nm leads to the formation of non-radiative recombination centers with an activation energy of 0.5 eV (NT = 8.4 × 1014 cm−3) and a shallow defect level at 0.20 eV. The last one leads to the appearance of additional doping, but its concentration is low (NT = 5 × 1014 cm−3) so it does not affect the photoelectric properties. However, further increase in thickness to 1600 nm, leads to significant growth of its concentration to (3–5) × 1015 cm−3, while the concentration of deep levels becomes 1.3 × 1015 cm−3. Therefore, additional free charge carriers appearing due to ionization of the shallow level change the band diagram from p-i-n to p-n junction at room temperature. It leads to a drop of the external quantum efficiency due to the effect of pulling electric field decrease in the p-n junction and an increased number of non-radiative recombination centers that negatively impact lifetimes in InGaAsN.

Investigation Of the low-dose-thermoluminescence characteristics of LiF:Mg,P

Thermoluminescence (TL) characteristics of LiF:Mg,P with varying concentrations (0.4%, 1% and 2%) of phosphorous are investigated and compared with those of the widely used TLD-100. The TL glow curves of the three LiF:Mg,P samples exhibited two apparent peaks around 120°C and 239°C. The TL response of each of the two peaks vary linearly with increasing dose (between 0.4mGy and 12.0mGy) for each of the three samples. The thermolumiscence intensities from samples with 0.4%, 1.0% and 2.0% of phosphorous concentration were respectively at least 26, 18 and 21 times that of TLD-100. TL response from a repeat use of a single aliquot of the samples with 0.4%, 1.0% and 2.0% of phosphorous concentration did not vary by more than 6%, 8% and 10% respectively. There were 3%, 10% and 12% fading of TL response over three-week storage period at room temperature for samples with 0.4%, 1.0% and 2.0% of phosphorous concentration. Pre-irradiation annealing up to 600°C did not affect the glow curves structures of all the samples. However, while the sensitivity of samples B and C did not change with the annealing, the intensity of sample A first decreased with temperature up to 500°C before it significantly rose to a value above that of the unannealed sample. TL intensity of the sample annealed at 500°C decreased with increasing annealing duration up till one hour beyond which it remains constant. The linearity of the dose-response, negligible fading of response and unchanged sensitivities with pre-irradiation annealing for samples B and C qualify them as suitable TL dosemeters.

Microstructural evolution and magnetic properties of ultrafine solute-atom particles formed in a Cu75–Ni20–Fe5 alloy on isothermal annealing

Microstructural features strongly affect magnetism in nano-granular magnetic materials. In the present work we have investigated the relationship between the magnetic properties and the self-organized microstructure formed in a Cu75–Ni20–Fe5 alloy comprising ferromagnetic elements and copper atoms. High resolution transmission electron microscopy (HRTEM) observations showed that on isothermal annealing at 873 K, nano-scale solute (Fe,Ni)-rich clusters initially formed with a random distribution in the Cu-rich matrix. Superconducting quantum interference device (SQUID) measurements revealed that these ultrafine solute clusters exhibited super-spinglass and superparamagnetic states. On further isothermal annealing the precipitates evolved to cubic or rectangular ferromagnetic particles and aligned along the 〈100〉 directions of the copper-rich matrix. Electron energy-band calculations based on the first-principle Korringa–Kohn–Rostocker (KKR) method were also implemented to investigate both the electronic structure and the magnetic properties of the alloy. Inputting compositions obtained experimentally by scanning transmission electron microscopy–electron dispersive X-ray spectroscopy (STEM–EDS) analysis, the KKR calculation confirmed that ferromagnetic precipitates (of moment 1.07μB per atom) formed after annealing for 2 × 104 min. Magneto-thermogravimetric (MTG) analysis determined with high sensitivity the Curie temperatures and magnetic susceptibility above room temperature of samples containing nano-scale ferromagnetic particles.

Analysis of the Tb3+ recombination in ion implanted AlxGa1−xN (0≤x≤1) layers

AlxGa1−xN layers with different AlN molar fractions, 0≤x≤1, implanted with Tb3+ ions were characterized using structural and optical techniques. After adequate thermal annealing treatments, all the layers evidence the 5D4→7FJ intra-4f8 transitions. The green emission from the 5D4 emitting level can be identified up to room temperature in samples with x≥0.53. The preferential population paths of the Tb3+ luminescence were assessed by photoluminescence excitation at RT where two main broad subgap excitation bands peaked at ~270nm and ~300nm were found for the layers with higher aluminium content. The analysis of the temperature-dependent Tb3+ integrated luminescence reveals distinct activation energies for different compositions, with AlN:Tb showing the highest thermal stability for the intraionic luminescence. The ion excitation paths are discussed on a basis of excitonic features and compared with the trend observed for other rare earth ions in nitrides, as well as theoretical predictions. A single exponential decay for the 5D4→7F6 transition was measured at RT and the lifetime of the transition was found to increase with increasing composition revealing the sensitivity of the ions to the surrounding medium.

Magnetic properties of Co x Pt 100−x nanoparticles

CoxPt100−x nanoparticles (x = 50, 59, and 73) were prepared by the chemical reduction of Cobalt (II) chloride and Chloroplatinic acid, then ultrasonicated for 2 h. After annealing at various temperatures from 450 °C to 700 °C for 1 h, structure change was observed and samples show hard magnetic properties which depend strongly on chemical composition and annealing temperature. The highest coercivity value of 1.15 kOe was obtained at room temperature for sample with x = 50 annealed at 500 °C. Chemical reduction combined with ultrasound is a useful method to prepare CoPt nanoparticles.

The effect of ZnO addition on the phase transformation, microstructure, and ionic conductivity of 8YSZ ceramics

In this paper the effect of zinc oxide (ZnO) addition on the phase transformation and ionic conductivity of 8 mol % Yttria-stabilised Zirconia (8YSZ) is investigated. Pure 8YSZ and ZnO doped YSZ ceramics are prepared using the solid state reaction method sintered at 1550°C for 2 hours. The X-ray Diffraction (XRD) results reveal the presence of tetragonal, cubic and monoclinic phase of Zirconium dioxide (ZrO 2 ) for all undoped and doped YSZ sintered samples. The phase stability of tetragonal YSZ was found to be increased with the increase in ZnO addition. Minor fraction of monoclinic phase was found in pure YSZ sintered sample and the amount of monoclinic phase decreased with the increasing amount of Zn after sintering at 1550°C for 2 hours. The fraction of cubic phase was also found to decrease with the increase in Zn concentration. The highest ionic conductivity of 1.03×10 −3 S cm −1 was obtained at room temperature for samples with 3 mol% ZnO. Pure 8YSZ sintered sample on the other hand, yielded 9.88x10 −4 S cm −1 .

Imaging chemical concentration pattern and early stages of spinodal decomposition in the AgxNa1−xBr system by scanning force microscopy

In quasi binary systems like AgBr–NaBr the demixing from the homogeneous high temperature phase into separated phases is a complex process that depends on the ageing temperature as well as on the quench rate. Spinodal decomposition and nucleation processes can be distinguished which lead, however, to the same final equilibrium state. Using frequency modulated scanning force microscopy we aimed to distinguish the demixed phases and their morphologies on a nm-scale at room temperature for samples with different concentration. While no contrast between the different phases are observed in the usual topographic mode, a modified evaluation of Kelvin experiments allows the distinction of silver- and sodium enriched phases. Moreover, direct evidence is found for concentration fluctuations which are characteristic for spinodal decomposition.

Structure, magnetic and dielectric properties of nanocrystalline Se−xFe

Nanocrystalline Se–xFe (x=3 and 5wt%) samples were prepared by solid state reaction. XRD revealed the presence of two phases; FeSe2 and Se. HRTEM showed the epitaxial growth of FeSe2 on Se. The magnetization measurements showed ferromagnetic behavior above room temperature for sample with x=5wt%. The a.c. conductivity for x=3wt% follows the overlapping large polaron tunneling model, while for (x=5wt%) sample it follows the correlated barrier hoping model. The temperature dependence of the dielectric measurements revealed an anomaly above room temperature for (x=5wt%) sample, while it appeared at room temperature for (x=3wt%) sample.

A comparative study of high temperature properties of cobalt-free perovskites

Co-free perovskites with chemical composition Ba0.5Sr0.5Fe0.8M0.2O3-δ (M = Ni, Cu, Zn) were synthesized by the modified Pechini method, and their structure and microstructure were characterized by XRD and SEM. Oxygen content, electrical resistivity and Thermal Expansion Coefficient (TEC) were evaluated in air between room temperature and 900 °C. The high-temperature properties of these perovskites were compared with those of Co containing Ba0.5Sr0.5Fe0.8Co0.2O3-δ perovskite. The highest electrical conductivity was obtained for Ba0.5Sr0.5Fe0.8Cu0.2O3-δ, with values of 47.6 Scm−1 at 544 °C. This same composition also exhibits the highest oxygen vacancies concentration: 3-δ = 2.61 at room temperature. In contrast, the Ba0.5Sr0.5Fe0.8Zn0.2O3-δ, showed lower electrical conductivity suggesting that the Zn+2 ions block electron transport. Co-free perovskites seem to be stable at high temperatures for long term periods. However, these compounds suffered degradation at room temperature in samples stored in air.

Structural and optical characterizations of InPBi thin films grown by molecular beam epitaxy

InPBi thin films have been grown on InP by gas source molecular beam epitaxy. A maximum Bi composition of 2.4% is determined by Rutherford backscattering spectrometry. X-ray diffraction measurements show good structural quality for Bi composition up to 1.4% and a partially relaxed structure for higher Bi contents. The bandgap was measured by optical absorption, and the bandgap reduction caused by the Bi incorporation was estimated to be about 56 meV/Bi%. Strong and broad photoluminescence signals were observed at room temperature for samples with xBi < 2.4%. The PL peak position varies from 1.4 to 1.9 μm, far below the measured InPBi bandgap.