High Pyroelectric Figure Of Merit Research Articles

A simple, low-temperature fabrication method of highly (100)-oriented (Na0.85K0.15)0.5Bi0.5TiO3 thin films with outstanding electric properties

Abstract In this paper, we propose a simple but effective method to prepare high-quality (100)-oriented (Na0.85K0.15)0.5Bi0.5TiO3 (NKBT) thin films with outstanding electric properties by a sol-gel spin-on technique. By introducing a LaNiO3 seed layer between the substrate and thin film, we simultaneously achieved crystallization at temperatures as low as 450 °C and controlled orientation. X-ray diffraction and X-ray reflectometry indicated that the NKBT/LNO thin film annealed at 500 °C was highly (100)-oriented, and had clear interfaces without diffusion, effectively reducing the dielectric constant and leakage current. Additionally, due to its high (100) orientation and clear interface, the NKBT thin film annealed at 500 °C had high displacement and a high pyroelectric coefficient, giving it a higher pyroelectric figure of merit than those of previously reported films. This study provides a new and simple method for preparing highly oriented lead-free thin films at low temperatures, and it extends the possible applications of these films to integration with silicon substrates.

CaxSr0.3−xBa0.7Nb2O6 lead-free pyroelectric ceramics with high depoling temperature

CaxSr0.3−xBa0.7Nb2O6 [CSBN (x), x = 0.00, 0.10, 0.20, and 0.30] lead-free ceramics were fabricated by traditional solid-state reaction technique. The morphology, structure, dielectric, ferroelectric and pyroelectric properties of CSBN (x) ceramics were systematically studied. The thermal depoling behaviors were evaluated through measurements of temperature dependence of piezoelectric constant (d33). All CSBN (x) ceramics exhibited obvious diffuse phase transitions and maximum dielectric constant (εm) increased monotonically with x. The ferroelectric and pyroelectric properties of CSBN (x) have been enhanced remarkably due to Ca addition. The remnant polarization (Pr) and pyroelectric coefficient (p) of CSBN (0.30) samples reached 4.95 μC/cm2 and 1.30 × 10−8C/cm2K which roughly tripled and doubled pure SBN. What's more, CSBN (0.20) samples achieved rather high pyroelectric figure of merit of voltage (Fv = 0.0203 m2/C) which is superior to many other lead-free materials and pyroelectric figure of merit of detectivity (FD) for CSBN (0.20) and CSBN (0.30) samples both soared to 0.61 × 10−5Pa−1/2. The most inspiring part is the depoling temperature and Curie temperature noticeably shifted to higher temperature region owing to Ca addition. These results unveil the potential of CSBN (x) ceramics for infrared detector applications.

Design and simulation of pyroelectric detectors with nanometer size spider-web for low thermal conductance

We report the design and simulation of uncooled pyroelectric detectors which utilizes a nanometer sized mesh or truss to support the suspended detector. Pyroelectric detector is a class of thermal detector in which the change in temperature causes the change in the spontaneous polarization in the sensing material. Ca modified lead titanate (PCT) was selected as the thermometer in the detector because of its high pyroelectric figure of merit. The design and simulation of pyroelectric detectors have been conducted by simulating the structure with Intellisuite™. Finite element method (FEM) was used to simulate the structural and thermal properties of the device. The simulated detectors had a spider web-like structure with each of the strut (ring) of spider web had a width of 100 nm. In the design, the pyroelectric detectors utilized Ni0.8Cr0.2 absorber, PCT sensing layer, Ti electrodes, Al2O3 structural layer to obtain low thermal conductance between the detector and Si substrate. Three different types of pyroelectric detectors were designed and analyzed. The first design had linear electrode and simple spider web support. The value of the thermal conductance of this detector was found to be 3.98 × 10ź8 W/K. The second design had a longer thermal path than the first one and the thermal conductivity of this device was found to be 2.41 × 10ź8 W/K. High detectivity was obtained by reducing the thermal conductance between the sensing layer and the substrate or the heat sink in the third design. The design was optimized for the best result by modifying the shape, dimension and thickness of various layers namely absorber, electrodes, sensing layer, and struts. The thermal conductance between the sensor and the substrate using the third design was found to be as low as 4.57 × 10ź9 W/K which is significantly lower than previously reported values. The thicknesses of the web structure, web support, electrodes, sensing layer, and absorber of the final structure were 2, 1, 0.5, 2, and 0.2 µm respectively for this value of thermal conductance. The absorber diameter was 50 µm and the diameter of the spider web was 200 µm. A total of 80 struts with 100 nm width were used in the design.

Doped TGS crystals for IR detection and sensors

Triglycine sulfate crystals (TGS) doped with l- and d-alanine, respectively, where grown in paraelectric phase at 52 °C. They show stable parameters versus pure TGS crystals, lower permittivities and losses, i.e. higher pyroelectric figure of merit. l- and d-alanine-doped crystals show a mirror asymmetry of the growth habit along the ferroelectric axis. Hysteresis loop of pure and doped samples were automatically recorded. Internal bias field of about 1 kV/cm, induced by the two dopants, stabilizes the polarization components P + and P − in opposite directions. Spontaneous polarization of doped crystals shows two unequal P +/P − components, having a peculiar dependence on the ac applied electric field. Dopage simulation of pure TGS samples, using several bias fields, shows even more complicated pattern. Pyroelectric coefficients were evaluated from pyroelectric current measurements. A remarkable asymmetry of the pyroelectric coefficient peak values for the enantiomorphous-doped crystals was noticed, crossing up and down the Curie point. This fact suggests a non-equivalent l/ d-alanine dopant substitution of the glycine group GI in the host lattice. It has been shown that the pyroelectric coefficient can be increased at room temperature, under an optimized dc electric field applied on the pyroelectric wafer. Doped crystals are suitable for IR detector and for more stable gas sensors applications in pollution monitoring.

Doped TGS crystals for IR detection and sensors

Triglycine sulfate crystals (TGS) doped with l - and d -alanine, respectively, where grown in paraelectric phase at 52 °C. They show stable parameters versus pure TGS crystals, lower permittivities and losses, i.e. higher pyroelectric figure of merit. l - and d -alanine-doped crystals show a mirror asymmetry of the growth habit along the ferroelectric axis. Hysteresis loop of pure and doped samples were automatically recorded. Internal bias field of about 1 kV/cm, induced by the two dopants, stabilizes the polarization components P + and P − in opposite directions. Spontaneous polarization of doped crystals shows two unequal P + /P − components, having a peculiar dependence on the ac applied electric field. Dopage simulation of pure TGS samples, using several bias fields, shows even more complicated pattern. Pyroelectric coefficients were evaluated from pyroelectric current measurements. A remarkable asymmetry of the pyroelectric coefficient peak values for the enantiomorphous-doped crystals was noticed, crossing up and down the Curie point. This fact suggests a non-equivalent l / d -alanine dopant substitution of the glycine group GI in the host lattice. It has been shown that the pyroelectric coefficient can be increased at room temperature, under an optimized dc electric field applied on the pyroelectric wafer. Doped crystals are suitable for IR detector and for more stable gas sensors applications in pollution monitoring.

Study of pyroelectric activity of PZT/PVDF-HFP composite

Flexible, free-standing piezo and pyroelectric composite with 0 to 3 connectivity was made up from Lead Zirconate Titanate (PZT) powder and poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) copolymer. The pyroelectric and the piezoelectric longitudinal (d33) coefficients were measured. A 50/50 vol.% PZT/PVDF-HFP composite resulted in piezo and pyroelectric coefficients of d33 = 25.0 pC/N and p = 4.5 × 10-4 C/m²K at 70 °C, respectively. Analysis of the complex permittivity in a wide range of frequency was carried out indicating lower permittivity of the composite in comparison with a permittivity of the PZT ceramic. The low value of the permittivity gives a high pyroelectric figure of merit indicating that this material can be used to build a temperature sensor in spite of the lower pyroelectric coefficient compared with PZT.

Electrical properties of ceramic/polymer composites

Three types of ceramic/polymer composites were prepared and their electrical, dielectric and pyroelectric properties analyzed. The composite PZT5/VDF-TrFE shows a significantly higher pyroelectric figure of merit than PZT (VDF=vinylidine fluoride, TrFE=trifluoroethylene). The dielectric loss of the ceramic/polymer composites is observed to be dominated by those of the polymer, whereas the ceramic phase has a significant contribution on the steady-state electrical conduction and low-frequency dielectric loss at high temperatures. >

ADTGSP single crystal with high pyroelectric figure of merit

Abstract This paper reports the distribution coefficient of phosphoric acid in solid-liquid phases and the conditions for the stepwise synthesis of chemical materials of ADTGSP crystals. The transparent bulk ADTGSP crystals were grown by lowering temperature method. The pyroelectric, dielectric, ferroelectric properties of ADTGSP crystal were measured and it is found that this crystal possesses higher pyroelectric figure of merit than that of TGS and DTGS crystals.

Glass Bonded Crystalline Boracite Composites for Pyroelectric Applications

Polymer and glass bonded crystalline boracite composites are prepared for large area device applications. The glass bonded composites show large pyroelectric figure of merit at room temperature and at 65°C the value becomes larger than that of TGS single crystal (1×10-5 C/m2K) measured at room temperature. Larger area boracite composites can be prepared. Such composites are easier to pole, give quite reproducible results and give higher pyroelectric figure of merit (p/K values) than the earlier reported values on Fe-I boracite single crystals.

Improper ferroelectrics for pyroelectric detection of infrared radiation

Abstract The absence of dielectric divergence in improper ferroelectrics makes it possible to obtain a high pyroelectric figure of merit near their transition temperature. Results of measurements carried out as a function of temperature on representatives of three classes of improper ferroelectrics: rare-earth molybdates, propionates, and boracites, show that in each of these the figure of merit rises to a peak value which is superior to that of triglycine sulfate. Analysis of the experimental results using a Landau type free-energy model yields an estimate of the optimum figure of merit obtainable.