High Pyroelectric Coefficient Research Articles

Pyroelectric properties of sol–gel derived lithium tantalite thin films

Lithium tantalite (LiTaO 3) thin films (∼0.5 μm) have been successfully deposited on Pt(111)/ SiO 2/ Si(1 0 0) substrates by means of sol–gel spin-coating technology. Figures of merit for infrared detector were studied for the LiTaO 3 thin films. There exists high figures of merit F v of 2.1×10 −10 C cm/J and F m of 2.4×10 −8 C cm/J because of the relative low dielectric constant ( ε r) of 35 and high pyroelectric coefficient ( γ) of 4.0×10 −8 C/cm 2 K of the films. The pyroelectric infrared detector fabricated by the LiTaO 3 thin film exhibits a voltage reponsivity R v of 4584 V/W at 20 Hz and a high specific detectivity D ∗ of 4.23×10 7 cm Hz 1/2/ W at 100 Hz .

Change in the compositional distribution in perovskite solid solutions during the sintering by SPS

As an application of characteristic of spark plasma sintering (SPS) method, which can produce highly sintered material with almost no change in compositional distribution, sintered materials that consist of different compositions were prepared. Perovskite three component system, xPb(Zn 1/3Nb 2/3)O 3– yPbZrO 3–(1− x− y)PbTiO 3, exhibits a very sharp pyroelectric peak at phase transition temperature between F RL and F RH phases. When a mixture of calcined materials having different compositions of this system was sintered by SPS, the compositional distribution in the starting mixture was almost maintained. The sintered material exhibited high pyroelectric coefficient over a wide temperature range.

Investigations on the electrical and mechanical properties of triglycine sulphate single crystals modified with some rare earth metal ions

Single crystals of triglycine sulphate (TGS) modified with La 3+, Ce 3+ and Nd 3+ have been grown from aqueous solutions by low-temperature solution growth method. The effect of rare earth ion dopants (La, Ce and Nd) on the ferroelectric properties of TGS is reported. Dielectric constant and dielectric loss have been measured for different frequencies. Dielectric measurements revealed that the dielectric constant of Ce-doped TGS increases rapidly at the transition temperature. Piezoelectric d 33 coefficient has been measured for the rare earth ions modified TGS crystals. Among the three dopants, Nd-doped TGS possesses low dielectric constant and high pyroelectric coefficient suggesting that this can be a potential material for infrared detectors.

Dielectric and pyroelectric properties of PZFNT/PZT bimorph thin films

Pyroelectric Pb1,1(Zr0.58Fe0.2Nb0.2Ti0.02)O3/Pb1.1(Zr0.9Ti0.1)O3 (PZFNT/PZT) bimorph thin films are processed via a modified sol-gel method on highly textured (1 1 1)Pt/Ti/SiO2/Si substrates. XRD and SEM investigations show full pyrochlore to perovskite phase transformation after annealing at 750 °C. XPS depth profiling reveals diffusion of Fe leading to a broad transition layer. The PZT 90/10 bottom layer was shown to be effective for dielectric permittivity control of the bimorph structure. The small signal dielectric constant, e′, was determined as 580 at 10 kHz. The temperature dependence of e′ is shown to exhibit a single maximum at approximately 195 °C. The C–V characteristics of the bimorph structure show the typical behavior of ferroelectric perovskites. These results are attributed to microstructural effects, particularly the presence of a broad transition layer. The pyroelectric properties are reported in the temperature range from 20 to 60 °C and compared to monomorph PZT and PZFNT films. It is shown that the bimorph thin film has higher pyroelectric coefficient and detectivity than the constituent monomorph films.

Poling of multilayer Pb(Zr 0.3Ti 0.7)O 3/PbTiO 3 thin film for pyroelectric infrared sensor application

Poling of multilayer Pb(Zr 0.3Ti 0.7)O 3/PbTiO 3 thin films has been studied. Poling temperature and electrical field are optimised to achieve a high pyroelectric coefficient. The pyroelectric coefficient is found to saturate when a sufficient high poling electric field (∼350 kV/cm) is applied at room temperature. Further improvement of the pyroelectric properties is achieved with the increasing of poling temperature (up to 180 °C). Pyroelectric coefficient of the poled PZT/PT film (at 350 kV/cm, 180 °C) is measured using a modified Byer–Roundy method to be 250 μC/m 2 K. Compared with the pure Pb(Zr 0.3Ti 0.7)O 3 thin film, the multilayer PZT/PT thin film has a lower pyroelectric coefficient, however, its dielectric constant and dielectric loss are reduced. Thus the multilayer PZT/PT film has higher figures of merit for pyroelectric application.

Dielectric properties of 65PMN–35PT/P(VDF–TrFE) 0–3 composites

Lead magnesium niobate–lead titanate (PMN–PT with 35 mol.% PT) single crystal powder has been incorporated into a polyvinylidene fluoride–trifluoroethylene (P(VDF–TrFE) 70/30 mol.%) copolymer matrix to form 0–3 composites. With 65/35 mol.% composition, PMN–PT has high piezoelectric properties as a result of the enhanced polarizability arising from the coupling between two equivalent energy states. P(VDF–TrFE) ferroelectric copolymer films can be poled to give piezoelectric and pyroelectric performance without prior mechanical stretching. The composites were prepared using solvent casting to disperse the single crystal powder homogeneously in the matrix. Composites with PMN–PT volume fraction φ ranging from 0.05 to 0.4 were fabricated using a hot-press method. The relative permittivity and pyroelectric coefficients of the composites were measured as a function of φ. Good agreement has been obtained between the theoretical and experimental values. Under the same poling condition, the composites have higher pyroelectric coefficient than the pure copolymer films. Hysteresis measurements reveal that the remanent polarization of composites increases as φ increases.

Preparation of 4:55:45 samarium doped PZT films by sol-gel technique and their characterization

Thin ferroelectric films of samarium doped PZT (4:55:45) were prepared by sol-gel technique on ITO coated corning 7059 glass. Characterization of these films by X-ray diffraction and scanning electron microscopy shows that the films are formed perovskite tetragonal phase with submicron crystallite size. Charge field hysteresis, dielectric relaxation and pyroelectric studies were carried on these films. It is concluded that these films with their high pyroelectric coefficient ∼45 nC cm −2 K −1 and low dielectric constant ∼230 will find application as pyroelectric sensor elements.

Pyroelectric and dielectric properties of sol–gel derived barium–strontium–titanate (Ba0.64Sr0.36TiO3) thin films

Abstract The barium–strontium–titanate (BST, Ba 0.64 Sr 0.36 TiO 3 ) thin films have been prepared by the sol–gel method on a platinum-coated silicon substrate. The resulting thin films show very good dielectric and pyroelectric properties. The dielectric constant and dissipation factor for Ba 0.64 Sr 0.36 TiO 3 thin film at a frequency of 200 Hz were 592 and 0.028, respectively. The dependence of the capacitance as a function of the voltage shows a strongly non-linear character, and two peaks characterizing spontaneous polarization switching can be clearly seen in this curve, indicating that the films have a ferroelectric nature. The capacitance changed from 495 to 1108 pF with the applied voltage in the −5 to +5 V range at a frequency of 100 kHz. The peak pyroelectric coefficient at 30 °C is 1080 μC/m 2 K. The pyroelectric coefficient at room temperature (25 °C) is 1860 μC/m 2 K, and the figure-of-merit of this film is 37.4 μC/m 3 K. The high pyroelectric coefficients and the greater figures-of-merit of Ba 0.64 Sr 0.36 TiO 3 thin films make it possible to be used for thermal infrared detection and imaging.

A study of pyroelectric and dielectric properties of alternate layer fluorodeconoylmonoitaconate Langmuir–Blodgett films

Abstract The pyroelectric effect of 1H, 1H1, 2H1, 2H- per fluorodeconoylmonoitaconate monomer/eicosylamine and 1H, 1H1, 2H1, 2H- per fluorodeconoylmonoitaconate polymer/eicosylamine alternate layer LB films has been studied in this work. The quasi-static method has been employed to measure the pyroelectric coefficients, dielectric constant and dielectric loss of these assemblies. Relatively high (for LB films) pyroelectric coefficients of 4.9 μC m−2 K−1 for the monomer/amine and 3.9 μC m−2 K−1 for the polymer/amine have been obtained.

Fabrication and electrical properties of Ba0.64Sr0.36TiO3 thin films by sol-gel on platinum coated silicon

The Ba0.64Sr0.36TiO3 thin films have been prepared by the sol-gel method on a platinum-coated silicon substrate. The structure and electrical properties of sol-gel derived Barium-strontium-titanate (Ba0.64Sr0.36TiO3) thin films have been investigated. The as-fired thin films are found to be amorphous, and the films crystallize to a perovskite structure after a post deposition annealing at 700°C for 1 h in air. The dielectric constant and dissipation factor for Ba0.64Sr0.36TiO3 thin film at a frequency of 200 Hz were 592 and 0.028, respectively. The temperature dependence of dielectric constant and dissipation factor exhibited a diffused ferroelectric to paraelectric phase transition at 40°C. The ferroelectric nature of this film at room temperature was confirmed by the existence of butterfly-shaped C-V curves caused by switching of the ferroelectric domains. The capacitance changed from 495 to 1108 pF with the applied voltage in the −5 to +5 V range at a frequency of 100 kHz. The pyroelectric coefficient at room temperature (25°C) is 1860 μC/m2K, and the figure-of-merit of this film is 37.4 μC/m3K. The high pyroelectric coefficients and the greater figures of merit of Ba0.64Sr0.36TiO3 thin films make it possible to be used for thermal infra-red detection and imaging.

High Pyroelectric Coefficients of Ca-Modified Lead Titanate Sol-Gel Thin Films Obtained by Multiple Deposition and Crystallization

Ferroelectric thin films of (Pb 0.76 Ca 0.24 )TiO 3 nominal composition have been obtained, by multiple spin-on deposition on Si-based substrates and RTP crystallization, from precursor solutions processed by the diol-based sol-gel method. A mixed <001>/<100> or <111> preferential orientations were promoted by appropriate choice of the substrate, as determined by XRD measurements. The effect of substrate annealing and crystallized film annealing on the pyroelectric coefficient of the films was determined and discussed. Poling of the films at room temperature and at 150 °C was tested. The highest pyroelectric coefficient achieved was n ∼ 40.0 2 10 m 9 Ccm m 2 K m 1 .

Electrical and pyroelectric properties of in-plane polarized lead lanthanum titanate thin film

Pb 0.9 La 0.1 Ti 0.975 O 3 (PLT10) thin films were deposited on SiO2/Si(100) substrates coated with a ZrO2 buffer layer. Studies by x-ray diffraction and scanning electron microscopy reveal that the ZrO2 film consists of both tetragonal and monoclinic phases, with the tetragonal phase being the dominant one. The PLT10 film has a perovskite structure and the grains in the film have a rather uniform size of about 50 nm. By using interdigital transducer (IDT) electrodes the in-plane electrical properties, hysteresis loop, and pyroelectric coefficient of the PLT10 film were measured. The dielectric constant and loss factor vary only slightly with frequency in the range 103–106 Hz, with the loss factor being less than 0.01 over the entire range. The leakage current density is lower than 2×10−8 A/cm2 at a bias field of 5 kV/cm. The remnant polarization and coercive field are 12.6 μC/cm2 and 9.93 kV/cm, respectively. The film exhibits a reasonably high pyroelectric coefficient (95 μC/m2 K) after it has been poled by applying 120 V ac at 0.1 Hz across the IDT electrodes.

Fabrication and Characterization of Pyroelectric Ba0.8Sr0.2TiO3 Thin Films by a Sol‐Gel Process

A sol‐gel process was used to prepare pyroelectric Ba0.8Sr0.2TiO3 thin films with large columnar grains (100–200 nm in diameter) on Pt/Ti/SiO2/Si substrates, via using a 0.05M solution precursor. The relationship between dielectric constant and temperature (ɛr‐T) showed two distinctive phase transitions in the Ba0.8Sr0.2TiO3 thin films. Both the remnant polarization and the coercive field decreased as the temperature increased from −73°C to 40°C. Its low dissipation factor (tan δ= 2.6%) and high pyroelectric coefficient (p= 4.6 × 10−4 C·(m2·K)−1 at 33°C), together with its good insulating properties, made the prepared Ba0.8Sr0.2TiO3 thin films promising for use in uncooled infrared detectors and thermal imaging applications.

A Molecular Pyroelectric Using a Chiral Zinc(II) Complex: High Pyroelectric Coefficient by Second-order Pyroelectricity

Abstract A chiral zinc complex [Zn(R-salphet)2] [R-salphet− = N-(R)-1-phenylethylsalicylideneiminate(1–)] showed second-order pyroelectricity in a starch matrix. The pyroelectric coefficient was found to be 2.0 ± 1.5 mC m−2 K−1, which is much greater than that of practical pyroelectric materials. The resonance and antiresonance frequencies were found to be 50 kHz and 90 kHz, respectively, from the admittance measurement. The electromechanical coupling factor was calculated to be 0.95.

Orientation effects on polarization and pyroelectric properties of ferroelectric thin films on Si

Oriented ferroelectric thin films (⩽ 1 μm) of PZT (90/10), Bi 4 Ti 3 O 12 , and La-modified Bi 4 Ti 3 O 12 , on Pt(111)/Ti/SiO 2 /Si(100) substrates were fabricated using (MOD) technique. Film orientation was controlled through heat treatment, composition and layer structure, and correlated to structural changes using XRD, SEM and RAMAN techniques. Measured properties included P – E hysteresis loop, static pyroelectric and fatigue behavior. Temperature stable (25–90°C) polarization with 2P r values of 6–24 μC/cm 2 and low switching fields E c =10–40 kV/cm were determined. For L-BIT films, low E c values are attributed to easier domain wall mobility with La ions on the different Bi sites, resulting in improved fatigue behavior, comparable to SBT films, at much lower switching fields (Scott, J. F., High-dielectric constant thin films for dynamic random access memories (DRAM). Ann. Rev. Mater. Sci ., 1998, 28 , 79–100; Joshi, P. C. and Krupanidhi, S. B., Switching, fatigue, and retention in ferroelectric Bi 4 Ti 3 O 12 thin films. Appl. Phys. Lett. , 1993, 62 , 1928–1930; Dimos, D., Al-Schareef, N. H., Warren, W. L. and Tuttle, B. A., Photoinduced changes in the fatigue behavior of SrBi 2 Ta 2 O 9 and Pb(Zr,Ti)O 3 thin films. J. Appl. Phys. , 1996, 80 , 1682–1687). High pyroelectric coefficients ∼10–60 nC/cm 2 K were also determined for the different films, up to ∼100°C.

Pyroelectricity of spontaneously poled La-modified lead titanate thin films on silicon based substrates

Multiple deposition by spin-coating and RTP crystallisation have been used to obtain La-modified lead titanate thin films of composition Pb 0.88 La 0.08 TiO 3 (PTL) onto two types of substrates : Ti/Pt/Ti/(100)Si annealed at 650°C and Pt/TiO 2 /(100)Si. The films on Ti/Pt/Ti/(100)Si present a main preferred crystallographic orientation, whereas the films on Pt/TiO 2 /(100)Si present a mixed / preferred orientation. All the films developed a net polarisation in the direction perpendicular to the film plane and a spontaneous pyroelectric coefficient. The hysteresis and switching characteristics of the films were dependent on the type of substrate. Results as a function of the number of deposited layers are presented. Poling was carried out under different electrical signals at 150°C. The highest pyroelectric coefficient achieved at room temperature was γ ∼40×10 -9 C cm -2 K -1 .

Preparation and pyroelectric properties of Bi4Ti3O12 based ceramics

The pyroelectric properties of Bi4Ti3O,12(BIT)-based ceramics have been investigated from the viewpoint of their application to pyro-sensor materials. Here, BIT ceramics are added with Nb2O5 for improving the electrical properties. Furthermore, lanthanum modified BIT ceramics with composition of (Bi4-xLax)Ti3O12+1.0mol% Nb2O5(x=0 ∼ 1.10) are also studied for obtaining higher pyroelectric coefficient in the wide temperature range because Tc of this system is decreasing with increase of the La2O3. Therefore, the compositionally graded materials in the BIT based ceramics may be expected to obtain much improved pyroelectric properties.

Pyroelectric properties and domain structure of modified lead ferroniobate-based ceramics

The present paper reports on a study of pyroelectric and dielectric properties and the domain structure of ferroelectric ceramics of PbFe0,5Nb0,5O3 and its solid solutions with PbTiO3 and PbZrO3. Wedge-shaped domains were observed in ceramics' grains. Extremely high pyroelectric coefficient values (determined by a dynamic technique) γd∼ 15.10-4 Cm-2K-1 were obtained in PbFe0,5Nb0,5O3 ceramics doped with 1 wt. % of Li2CO3.

Characterization of Fine‐Grained Bismuth Vanadate Ceramics Obtained Using Nanosized Powders

Nanocrystalline bismuth vanadate (n‐BiV) powders with a crystallite size of &lt;50 nm have been prepared, at room temperature, by subjecting a stoichiometric mixture of bismuth oxide and vanadium pentoxide to mechanical activation. The n‐BiV powders show enhanced sinterability, in comparison to the conventionally prepared micrometer‐sized bismuth vanadate (m‐BiV) powders and yield ceramics with a uniform microstructure. High‐density (∼98% of the theoretical value), fine‐grained (average grain size of ∼2 μm) ceramics, obtained using n‐BiV have a high dielectric constant and a high pyroelectric coefficient and are associated with low dielectric loss, both at room temperature and at the transition temperature. These fine‐grained ceramics show diffused phase transition and relaxor behavior, which are attributed to the irregular distribution of defects and/or compositional inhomogeneities in these ceramics. The fine‐grained ceramics exhibit ferroelectric hysteresis loops with higher remanent polarization and lower coercive field values than the coarse‐grained ceramics.

Pyroelectric Ba0.8Sr0.2TiO3 thin films derived from a 0.05 M solution precursor by sol–gel processing

Tetragonal Ba0.8Sr0.2TiO3 thin films with large columnar grains 100–200 nm in diameter have been prepared on Pt/Ti/SiO2/Si substrates using a 0.05 M solution precursor by sol–gel processing. The ferroelectric phase transition in the prepared Ba0.8Sr0.2TiO3 thin films is broadened, and suppressed to 40 °C with a maximum dielectric constant of εr (100 kHz)=680. The observed low dissipation factor tan δ=2.6% and high pyroelectric coefficient p=4.586×10−4 C/m2 K at 33 °C render the prepared Ba0.8Sr0.2TiO3 thin films promising for uncooled infrared detector and thermal imaging applications.