Secondary Pyroelectric Effect Research Articles

High‐performance Pyroelectric Property Accompanied by Spin Crossover in a Single Crystal of Fe(II) Complex

AbstractPyroelectric materials hold significant potential for energy harvesting, sensing, and imaging applications. However, achieving high‐performance pyroelectricity across a wide temperature range near room temperature remains a significant challenge. Herein, we demonstrate a single crystal of Fe(II) spin‐crossover compound shows remarkable pyroelectric properties accompanied by a thermally controlled spin transition. In this material, the uniaxial alignment of polar molecules results in a polarization of the lattice. As the molecular geometry is modulated during a gradual spin transition, the polar axis experiences a colossal thermal expansion with a coefficient of 796×10−6 K−1. Consequently, the material's polarization undergoes significant modulation as a secondary pyroelectric effect. The considerable shift in polarization (pyroelectric coefficient, p=3.7–22 nC K−1cm−2), coupled with a low dielectric constant (ϵ′=4.4–5.4) over a remarkably wide temperature range of 298 to 400 K, suggests this material is a high‐performance pyroelectric. The demonstration of pyroelectricity combined with magnetic switching in this study will inspire further investigations in the field of molecular electronics and magnetism.

High-performance Pyroelectric Property Accompanied by Spin Crossover in a Single Crystal of Fe(II) Complex.

Pyroelectric materials hold significant potential for energy harvesting, sensing, and imaging applications. However, achieving high-performance pyroelectricity across a wide temperature range near room temperature remains a significant challenge. Herein, we demonstrate a single crystal of Fe(II) spin-crossover compound shows remarkable pyroelectric properties accompanied by a thermally controlled spin transition. In this material, the uniaxial alignment of polar molecules results in a polarization of the lattice. As the molecular geometry is modulated during a gradual spin transition, the polar axis experiences a colossal thermal expansion with a coefficient of 796×10-6 K-1. Consequently, the material's polarization undergoes significant modulation as a secondary pyroelectric effect. The considerable shift in polarization (pyroelectric coefficient, p=3.7-22 nC K-1cm-2), coupled with a low dielectric constant (ϵ'=4.4-5.4) over a remarkably wide temperature range of 298 to 400 K, suggests this material is a high-performance pyroelectric. The demonstration of pyroelectricity combined with magnetic switching in this study will inspire further investigations in the field of molecular electronics and magnetism.

Pyroelectric effect in doped nonpolar glycine crystals

Doping-induced local symmetry breaking of centrosymmetric molecular crystals endows them with piezoelectric and pyroelectric properties. In this work, we measured temperature dependences of pyroelectric and piezoelectric coefficients in α--glycine crystals single-doped by threonine and double-doped by threonine and alanine. We analyzed primary and secondary pyroelectric effects in these crystals and suggested a model of the dopant complexes related to the observed effects. Keywords: pyroelectricity, α-glycine, doped molecular crystals.

Исследование пироэлектрического эффекта в легированных неполярных кристаллах глицина

Doping-induced local symmetry breaking of centrosymmetric molecular crystals endows them with piezoelectric and pyroelectric properties. In this work, we measured temperature dependences of pyroelectric and piezoelectric coefficients in α-glycine crystals single-doped by threonine and double-doped by threonine and alanine. We analyzed primary and secondary pyroelectric effects in these crystals and suggested a model of the dopant complexes related to the observed effects.

Surface Piezoelectricity and Pyroelectricity in Centrosymmetric Materials: A Case of α-Glycine.

Surface pyroelectricity and piezoelectricity induced by water incorporation during growth in α-glycine were investigated. Using the periodic temperature change technique, we have determined the thickness (~280 µm) of the near surface layer (NSL) and its pyroelectric coefficient (160 pC/(K × cm2) at 23 °C) independently. The thickness of NSL remains nearly constant till 60 °C and the pyroelectric effect vanishes abruptly by 70 °C. The piezoelectric effect, 0.1 pm/V at 23 °C measured with an interferometer, followed the same temperature dependence as the pyroelectric effect. Abrupt disappearance of both effects at 70 °C is irreversible and suggests that water incorporation to α-glycine forms a well defined near surface phase, which is different form α-glycine because it is polar but it too close to α-glycine to be distinguished by X-ray diffraction (XRD). The secondary pyroelectric effect was found to be <14% of the total, which is unexpectedly small for a material with a large thermal expansion coefficient. This implies that water incorporation infers minimal distortions in the host lattice. This finding suggests a path for the control of the piezoelectric and pyroelectric effects of the crystals using stereospecific incorporation of the guest molecules.

Interrelation of electrocaloric and concomitant effects in lead magnesium niobate based ceramics

Electrocaloric effect (ECE) as well as field induced pyroelectric and piezoelectric effects were investigated in relaxor ceramics 0.84 PbMg1/3Nb2/3O3–0.14 PbTiO3–0.02 SrTiO3. Dielectric and elastic properties of the solid solution were also studied. To improve the accuracy and reliability of the results obtained, the electrocaloric temperature change δT was measured both by the well-known quasi-adiabatic technique with a contact temperature sensor and by the radiometric mid Infrared technique developed by the authors. The contribution of the secondary pyroelectric effect to the total pyroelectric and ECE was studied in detail. The effect of the induced piezoelectricity on the range of the temperature stability of pyroelectric and electrocaloric responses was shown. The resulting combination of material parameters at reasonable operating temperatures and electric fields, including both the possibility of increasing δT and the existence of its temperature-independent range from 10 to 80 °C, predestines the solid solution as a promising electrocaloric material.

Primary and secondary pyroelectric effects in macro-fiber composites

Materials like the Macro-fiber Composite (MFC) are employed in energy harvesting applications utilizing the piezoelectric effect. However, energy harvesting using the pyroelectric effect in MFCs is an unexplored topic. This paper takes strides in understanding the thermal micromechanical interactions that MFCs experience due to this effect and leads to a better understanding of how MFCs behave in thermal environments. In this work, the pyroelectric coefficient (primary and secondary) are estimated for P1 and P2 Macro-fiber Composites (MFCs) using micromechanical modeling and experimental techniques. The coefficient of thermal expansion (CTE) is estimated using micromechanical theory for both MFC types which is consequently used in the modeling of the pyroelectric coefficient. Secant based moduli are used to better approximate the properties of components of MFCs in the regime of linear elasticity. Two experiments are conducted to measure the pyroelectric coefficient under different boundary conditions. In the first experiment, the thermal expansion of the MFC is constrained in a Kevlar envelope, while in the second experiment, the MFC is epoxied onto a metal shim allowing restricted deformations. Thermal experiments were conducted in an altitude chamber where the resulting average pyroelectric coefficient is calculated for both experiments.

Secondary Pyroelectric Effect and Figure of Merit of Ferroelectric 0–3 Composites

By mixing lead‐free piezoelectric Li0.06(Na0.50K0.50)0.94NbO3 (LNKN) ceramic particles and polysiloxane, the authors synthesize a novel pyroelectric element that exhibits an enhanced secondary pyroelectric effect. The composite with an LNKN filler ratio of 30 vol% exhibits a homogeneous microstructure and a strong contact between the LNKN filler and the polysiloxane matrix. Thus, the secondary pyroelectric effect originating from such an interaction accounts for approximately half of the total pyroelectric coefficient (i.e 29 μC/m2K) and enhanced the figure of merit of the composite (1.1 μC/m2K).

Vapour growth, morphology, absolute structure and pyroelectric coefficient ofmeta-nitroaniline single crystals

The growth speed of (hkl) faces in the vapour phase, the absolute structure obtained by X-ray crystallography, and the value and the sign of the pyroelectric coefficient ofmeta-nitroaniline (mNA) were analysed in detail. Thein situobservation of morphologically well developed faces of several mNA crystals growing in evacuated ampoules reveals no pronounced growth speed anisotropy for polar faces defining the unique axis 2 of themm2 group. Scanning pyroelectric microscopy confirms mono-domain mNA crystals. X-ray measurements in the space groupPca21show that the molecular planes coincide with the {\bar 211} and {\bar 2\bar 1\bar 1} faces, and the nitro groups cover the {201} face in the opposite direction to the crystal tip, characterizing the polar habitus studied here. At room temperature, the sign of the pyroelectric coefficient is positive for a measured effective value of 6.3 µC m−2 K−1, in good agreement with values reported by other authors. From previous elastic and piezoelectric published data, the secondary pyroelectric effect was calculated to be positive and far greater than the effective one, yielding a negative value for the primary pyroelectric coefficient.

Primary pyroelectric transition temperatures of binary nitrides (AlN, GaN and InN)

The primary pyroelectric transition temperature of wurtzite nitrides (AlN, GaN and InN) has been explored theoretically from their thermal properties. The spontaneous and piezoelectric polarization modifies the thermal conductivity of nitrides. The thermal conductivity [Formula: see text] as a function of temperature including and excluding the polarization mechanism predicts a transition temperature [Formula: see text] between primary and secondary pyroelectric effects. Below [Formula: see text], thermal conductivity including polarization field [Formula: see text] is lesser than thermal conductivity excluding polarization field [Formula: see text]. This is due to negative thermal expansion in binary nitrides below [Formula: see text]; however, above [Formula: see text], [Formula: see text]. [Formula: see text] is significantly contributed by piezoelectric polarization above [Formula: see text] due to thermal expansion which is the reason for the secondary pyroelectric effect. The transition temperature [Formula: see text] for AlN, GaN and InN has been predicted as 100 K, 70 K and 60 K, respectively, which fit well with the prior literature studies. This report proposes that thermal properties’ study can reveal the role of acoustic phonons in pyroelectricity.

Comprehensive Pyro‐Phototronic Effect Enhanced Ultraviolet Detector with ZnO/Ag Schottky Junction

AbstractAs a coupling effect of pyroelectric and photoelectric effect, pyro‐phototronic effect has demonstrated an excellent tuning role for fast response p–n junction photodetectors (PDs). Here, a comprehensive pyro‐phototronic effect is utilized to design and fabricate a self‐powered and flexible ultraviolet PD based on the ZnO/Ag Schottky junction. By using the primary pyroelectric effect, the maximal transient photoresponsivity of the self‐powered PDs can reach up to 1.25 mA W−1 for 325 nm illumination, which is improved by 1465% relative to that obtained from the steady‐state signal. The relative persistent secondary pyroelectric effect weakens the height of Schottky barrier, leading to a reduction of the steady‐state photocurrent with an increase in the power density. When the power density is large enough, the steady‐state photocurrent turns into a reverse direction. The corresponding tuning mechanisms of the comprehensive pyro‐phototronic effect on transient and steady‐state photocurrent are revealed based on the bandgap diagrams. The results may help us to further clarify the mechanism of the pyro‐phototronic effect on the photocurrent and also provide a potential way to optimize the performance of self‐powered PDs.

Accounting for the various contributions to pyroelectricity in lead zirconate titanate thin films

An understanding of the pyroelectric coefficient and particularly its relationship with the applied electric field is critical to predicting the device performance for infrared imaging, energy harvesting, and solid-state cooling devices. In this work, we compare direct measurements of the pyroelectric effect under pulsed heating to the indirect extraction of the pyroelectric coefficient from adiabatic hysteresis loops and predictions from Landau-Devonshire theory for PbZr0.52Ti0.48O3 (PZT 52/48) on platinized silicon substrates. The differences between these measurements are explained through a series of careful measurements that quantify the magnitude and direction of the secondary and field-induced pyroelectric effects. The indirect measurement is shown to be up to 25% of the direct measurement at high fields, while the direct measurements and theoretical predictions converge at high fields as the film approaches a mono-domain state. These measurements highlight the importance of directly measuring the pyroelectric response in thin films, where non-intrinsic effects can be a significant proportion of the total observed pyroelectricity. Material and operating conditions are also discussed which could simultaneously maximize all contributions to pyroelectricity.

Temperature Dependence of the Pyroelectric Coefficient of AlScN Thin Films

The piezoelectric and pyroelectric properties of aluminum nitride (AlN) can be further enhanced by alloying AlN with scandium nitride (ScN). However, while the pyroelectric effect can strongly affect the performance of electroacoustic devices such as surface acoustic wave (SAW) resonators, the pyroelectric properties of aluminum scandium nitride (AlScN) and their thermal dependence are not well known. In this work, the crystallographic, microstructural, and pyroelectric properties of 900 nm thick pyroelectric Al1−xScxN thin films (x = 0 to 0.3) are investigated. All films have wurtzite‐type crystal structure and are highly c‐axis oriented. The pyroelectric coefficient in the temperature range of 20–80 °C is determined by measuring the generated current as a function of sinusoidal temperature excitation. The effective pyroelectric coefficient of AlScN increases by approximately 85% in the investigated composition range. Moreover, no temperature dependence of the effective pyroelectric coefficient is observed for all samples. The increase of the effective pyroelectric coefficient is explained qualitatively by considering the contribution of primary and secondary pyroelectric effect as well as the substrate clamping.

Pyroelectric effect and lattice thermal conductivity of InN/GaN heterostructures

The built-in-polarization (BIP) of InN/GaN heterostructures enhances Debye temperature, phonon mean free path and thermal conductivity of the heterostructure at room temperature. The variation of thermal conductivities (kp: including polarization mechanism and k: without polarization mechanism) with temperature predicts the existence of a transition temperature (Tp) between primary and secondary pyroelectric effect. Below Tp, kp is lower than k; while above Tp, kp is significantly contributed from BIP mechanism due to thermal expansion. A thermodynamic theory has been proposed to explain the result. The room temperature thermal conductivity of InN/GaN heterostructure with and without polarization is respectively 32 and 48 W m-1 K−1. The temperature Tp and room temperature pyroelectric coefficient of InN has been predicted as 120 K and −8.425μC m−2 K−1, respectively which are in line with prior literature studies. This study suggests that thermal conductivity measurement in InN/GaN heterostructures can help to understand the role of phonons in pyroelectricity.

Method for Determining the Grüneisen Parameter of Pyroelectrics

c  , where  is the volume thermal expansion parameter, cp is the specific heat capacity, and с0 is the volumetric speed of sound. The Gruneisen parameter is an important parameter entering into the equation of state of a condensed matter; therefore, its determination, both theoretical and experimental, is of sufficient interest. As an example, we consider a method suggested in [2] where the characteristics of a stress wave arising in the sample of the examined material as a result of fast heating by a laser radiation pulse were measured. The material was transparent for radiation. The soughtafter parameter was determined from these measurements and the energy absorbed in the material. In the present work, a method for determining the Gruneisen parameter of pyroelectrics is suggested from the characteristics of the electric response of a material sample exposed to a gamma rays or neutron pulse. The problem of the response was solved in [3, 4]. Below we briefly describe some results of these works with application to the problem being solved. We consider a plane capacitor in which a polarized pyroelectric serves as a dielectric. The capacitance of the capacitor is C0, the area of its plates is S, and the distance between the plates is L. The polarization vector P is perpendicular to the plates connected through the active resistance R. The capacitor is mechanically free. We choose the coordinate system so that the х axis coincides with the direction of the polarization vector, and the origin of coordinates is placed at the capacitor center of gravity. The capacitor is irradiated by an ionizing radiation pulse whose duration tn is much smaller than the thermal time constant of the capacitor, that is, heating of the pyroelectric material is adiabatic. The temperature is uniformly distributed in the material. The electric response of the pyroelectric to uniform heating is the sum of the primary and secondary pyroelectric effects [5]. The first of them determines the polarization change provided that the shape and volume of the pyroelectric sample remain constant upon heating; the second determines the polarization change attendant to free deformation of the sample.

Secondary effects in wide frequency range measurements of the pyroelectric coefficient ofBa0.6Sr0.4TiO3andPbZr0.2Ti0.8O3epitaxial layers

We describe measurements of the pyroelectric coefficient of epitaxial layers of ${\mathrm{Ba}}_{0.6}{\mathrm{Sr}}_{0.4}{\mathrm{TiO}}_{3}$ (BST) and ${\mathrm{PbZr}}_{0.2}{\mathrm{Ti}}_{0.8}{\mathrm{O}}_{3}$ (PZT) using a modulated laser as the heat source in the frequency range 1 Hz to 10 MHz. The pyroelectric coefficient is also measured as a function of applied static electric field and for films grown on ${\mathrm{SrTiO}}_{3}$, ${\mathrm{DyScO}}_{3}$, and ${\mathrm{GdScO}}_{3}$ substrates. The heat diffusion equation is solved in cylindrical coordinates for the temperature field in a multilayer sample heated by a Gaussian-shaped laser beam. The secondary contribution to the pyroelectric effect caused by piezoelectric effects and in-plane thermal expansion is revealed by the difference between the pyroelectric coefficients at high and low frequencies. The secondary pyroelectric effect has the same dependence on applied field as the pyroelectric coefficient. The magnitude of the secondary effect changes with heating frequency because of changing mechanical conditions, but the pyroelectric coefficient has no other frequency dependence between 1 Hz and 10 MHz. The secondary effect is approximately 15% and 20% of the total pyroelectric response for PZT and BST films, respectively.

Phase transitions and thermal expansion in pyroelectric energy conversion

This paper elucidates dynamic effects of phase transitions and thermal expansion on pyroelectric energy conversion. The Olsen cycle was performed on [001]-oriented 0.72PbMg1/3Nb2/3O3−0.28PbTiO3 (PMN-28PT) single crystals at different frequencies with electric field cycled between 0.2 and 0.75 MV/m and temperature between 22 and 140 ∘C. The measured energy density more than doubled as frequency increased from 0.0173 to 0.0211 Hz. This was attributed to secondary pyroelectric effect caused by thermal expansion. At 0.0211 Hz, the samples transitioned from pseudocubic to highly polarized tetragonal phase during cooling. At lower frequency, it underwent additional phase transition from tetragonal to less polarized monoclinic phase.

Electrical, dielectric and pyroelectric behavior of neodymium substituted barium zirconium titanate

Neodymium (Nd) substituted barium zirconium titanate with nominal composition (Ba 1− x Nd x )(Zr 0.52Ti 0.48)O 3 [ x = 0.1, and 0.2] were synthesized using solid state reaction method. X-ray analysis confirmed the formation of perovskite structure along with minor pyroclore phase of neodymium. The change in grain size revealed the influence of Nd-ions on the microstructure. The sintered samples exhibited negative temperature coefficient of resistance (NTCR) and superior semiconducting behavior. Addition of Nd 3+varies the room temperature resistivity of Ba(Zr 0.52Ti 0.48)O 3. As the concentration of Nd-ion increased, the value of temperature dependent dielectric constant decreased whereas the Curie temperature of the ceramics shifted toward higher temperature side showing diffuse phase transition. This is attributed to decrease in average grain size. Temperature dependent pyroelectric current exhibited combination of primary and secondary pyroelectric effect.

Analysis of Pyroelectric Figures of Merit by Using Off Polar Axis Cut Crystals

Crystal cutting angles are critical for the pyroelectric device fabrication and performance optimization. In this report, we evaluated two pyroelectric figures of merit, p/ϵ and p/√ϵ, in all directions in space and suggested the crystallographic rotating angles having potential to maximize the effect. The polarization directions of the secondary pyroelectric effects are also evaluated for several crystal systems. It appears that the directions of the secondary pyroelectric effect, coupled through the piezoelectric, thermal expansion and elastic stiffness effect, follow those of the primary and thus the total pyroelectric effect in various crystallographic polar groups. Selected materials of interest with reported properties are examined and shown improvements of pyroelectric figure of merit p/ϵ by off polar axis cutting. The pyroelectric figures of merit of a specific material, TGS, are calculated with respect to its crystal orientation. The results show an appreciate improvement of pyroelectric figure of merit for the large area sensors applications. As for the point detectors (figure of merit, p/√ϵ), the pyroelectric figure of merit remains maximum along the polar axis, p2. The results are discussed in view of designing various pyroelectric sensing and imaging devices for several crystallographic polar point group materials.

The role of the secondary pyroelectric effect in a ferroelectric relaxor 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3

The depth profile of the pyroelectric coefficient effective values of a 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 (PMN-0.28PT) single crystal is studied. It was shown that owing to high pyroelectric coefficients the secondary pyroelectric effect significally contributes (∼40%) to the total pyroelectric coefficient.