Pyroelectric Measurements Research Articles

Influence of the magnetic field on the stability of the multiferroic conical spin arrangement of Mn0.80Co0.20WO4

The evolution of the low temperature antiferromagnetic conical (characterized by two, commensurate and incommensurate propagation vectors), and the high temperature collinear spin arrangements of the 20% Co-doped MnWO4 multiferroic has been studied in the presence of magnetic field up to 60 T by means of macroscopic magnetic and pyroelectric measurements, and by neutron diffraction experiments in fields up to 12 T on a single crystal. The complete magnetoelectric phase diagrams for magnetic fields along distinct magnetic directions with respect to the spin structure have been constructed up to magnetic field values exceeding those necessary to induce a spin-flip transition into the paramagnetic state. The differences in the topology of the diagrams are discussed. The obtained results might be common for other magnetic materials possessing conical antiferromagnetic structures.

Architecture of nanoscale ferroelectric domains in GaMo4S8

Local-probe imaging of the ferroelectric domain structure and auxiliary bulk pyroelectric measurements were conducted at low temperatures with the aim to clarify the essential aspects of the orbitally driven phase transition in GaMo4S8, a lacunar spinel crystal that can be viewed as a spin-hole analogue of its GaV4S8 counterpart. We employed multiple scanning probe techniques combined with symmetry and mechanical compatibility analysis to uncover the hierarchical domain structures, developing on the 10-100 nm scale. The identified domain architecture involves a plethora of ferroelectric domain boundaries and junctions, including primary and secondary domain walls in both electrically neutral and charged configurations, and topological line defects transforming neutral secondary walls into two oppositely charged ones.

Demonstration of a pyroelectric wireless temperature sensor

Energy generation systems operating at high temperatures are becoming increasing dependent on real-time measurements to enhance the overall performance. Since most sensors in energy systems are exposed to high temperature, high pressure, or corrosive environments where wiring is not desirable, harsh environment temperature sensing is preferred to be measured wirelessly. In this study, Pb(Zr0.52Ti0.48)O3 (PZT) pyroelectric ceramic was used to develop a wireless temperature sensor. An electromagnet was built with a set number of loops of wire, length, and radius. A PZT ceramic exposed to a heating source to induce a rate of temperature change with time. Generated current from the PZT due to experiencing a rate of temperature change with time was then supplied to the electromagnet to generate a magnetic field. The magnetic field was measured remotely with a milligaussmeter. The electromagnet was first characterized by measuring the magnetic field at different distances from the edge of the electromagnet along its axis. The milligaussmeter was able to detect the magnetic field generated by PZT pyroelectric ceramics at the specified distances from the electromagnet. A PZT sensor with a thickness of 0.1 cm was tested for use in a wireless temperature measurement configuration. Due to the non-linear pyroelectric response of PZT, the temperature dependent pyroelectric coefficient of PZT was also measured with a dynamic pyroelectric measurement technique in the temperature range from room temperature to 122 °C. The temperature dependent pyroelectric coefficient of PZT was found to increase from −40 × 10−5 C m−2 °C to −71.84 × 10−5 C m−2 °C. The PZT sensor was then tested for wireless temperature measurement applications at 100 °C, 150 °C, and 200 °C, and showed a maximum 10% deviation from baseline measurements.

Pyroelectricity in graphene oxide doped P(VDF-TrFE) films

The pyroelectric properties of polyvinylidene fluoride/trifluoroethylene doped with graphene oxide were studied. The pyroelectric current measurements were performed for polarized and non-polarized samples with different amount graphene oxide: 5, 10, 15, 20, 25%. The polarization process influence on pyroelectric current was discussed. Moreover the impact of different amount of dopant on pyroelectric properties of polyvinylidene fluoride/trifluoroethylene was analyzed. On the basis of obtained results the phase diagram was performed.

Magnetic field-induced ferroelectricity in S\u2009=\u20091/2 kagome staircase compound PbCu3TeO7

Ni3V2O8 is an archetypical multiferroic material with a kagome staircase structure of S = 1 (Ni2+) spins whose complex interplay between spin ordering and ferroelectricity has been studied for more than a decade. Here, we report a new kagome staircase compound PbCu3TeO7 with Cu2+ (S = 1/2) spins that exhibits two Néel temperatures at TN1 = 36 K and TN2 = 24 K, and a magnetic field (H)-induced electric polarization (P) below TN2. Pyroelectric and magnetoelectric current measurements in magnetic fields up to 60 T reveal that for H||c of ~ 8.3 T, a spin-flop transition induces a transverse P||a with a magnitude of 15 µC/m2 below TN2. Furthermore, for a parallel configuration with P//H//a, two spin-flop transitions occur, the first at ~ 16 T with P//a of 14 µC/m2, and the second at ~ 38 T, where P disappears. Monte Carlo simulations based on 12 major exchange interactions uncover that a sinusoidal amplitude modulation of the spins occurs along the b-axis below TN1 and an incommensurate, proper screw-type spin order occurs in the ac-plane below TN2. The simulation results show that P//a under H//c stems from a spin-flop transition facilitating an ab-plane-type spiral order, while the two successive spin-flop transitions for H//a result in spiral spin orders in the ab- and bc-planes. Based on the experimental and theoretical results, we establish field-induced magnetic and electric phase diagrams for the two H directions, demonstrating that the distorted kagome staircase structure with competing intra–interlayer interactions and lifted frustration creates a plethora of different noncollinear spin textures of S = 1/2 spins that in turn induce electric polarization.

Magnetic and ferroelectric properties of Indium-doped gallium ferrite

Indium-doped Ga1−xInxFeO3 (GIFO) with x = 0–0.15 were prepared by solid state reaction. Structural, magnetic and electric properties of the samples were studied. All specimen could be well indexed by the polar Pc21n space group and no phase transition was observed. Saturated magnetization exhibits a maximum at light doping sample of Ga0.95In0.05FeO3 due to the enhancement of the distortion, showing a correspondence with the variation of Fe3+ distribution difference between two forms of sites. Pyroelectric measurements show an increase of polarization after doping. The results indicate that both magnetism and ferroelectricity of GaFeO3 can be optimized by In doping.

Reassess study of high temperature electric transport properties of PbTiO3

In the present study we obtained the detailed dielectric properties of PbTiO3. The formation of the materials was confirmed through basic structural analysis using x-rays diffraction collected at room temperature. Differential scanning calorimetry confirms a first order phase transition at 763 K. Furthermore, DC conductivity as well as pyroelectricity measurements were conducted in the temperature range (400–823 K), from which the polarizability as a function of temperature was evaluated. On the other hand, AC conductivity behavior as a function of both temperature and frequency (0.12–102 kHz), shows a semiconducting like behavior indicating an adiabatic conduction mechanism. While the ferroelectric phase transition was established at 763 K from the permittivity data as a function of temperature. The behavior of the frequency and temperature exponents of the AC electrical conductivity confirm the correlated barrier hopping “CBH” mechanism of conduction. Thermal activation energy is obtained from DC and AC conductivity as well. Dielectric modulus was also studied as a function of both temperature and frequency.

Studying the Pyroelectric Effect in AlN Epilayers

We have studied the pyroelectric effect in 6- to 12-μm-thick AlN epilayers grown by hydride–chloride vapor phase epitaxy (HVPE) on 4H-SiC substrates. The pyroelectric current was generated by means of dynamic laser action. Evolution of the temperature fields was monitored by direct measurements of the surface temperature with allowance for the specific thermal heterogeneity of the AlN/SiC system. In combination with the results of pyroelectric current measurements, these data allowed the pyrocoefficient of the AlN/SiC structure to be estimated at p ≈ 3.0 μC/(m2 K). Pyroelectric figures of merit of the given structure are calculated that can be used for the comparison of pyroelectric materials intended for the creation of IR radiation detectors.

A dynamic method for the measurement of pyroelectric properties of materials

This study introduces a novel experimental set-up to measure the pyroelectric coefficient of materials at variable frequencies of temperature change. In this method, temperature changes are periodically applied through a mechanical set-up moving the sample between a hot and cold thermal reservoir in order to measure the current obtained from the sample’s pyroelectric conversion effect. For low frequencies of temperature change, an exponential equation is suggested for the temperature change in the sample based on a unidirectional heat flux through the sample. The pyroelectric coefficient can be determined from this model by fitting an exponential decay function to the pyroelectric current obtained from a single heating cycle. In comparison to other approaches for the measurement of the pyroelectric effect, the described method exhibits some advantages concerning flexibility, accuracy and simplicity, e.g. an almost deliberate adjustment of the rate of temperature change, the avoidance of electrical noise induced by continuously temperature-modulated heat stages and furnaces, a high accuracy of temperature control and the acceptance of samples made from different materials or with different sizes. The method is verified by pyroelectric coefficient measurements on a commercial PZT ceramic and on triglycine sulfate (TGS) single crystals, which have been grown by a temperature-lowering technique in our laboratory. Pyroelectric measurements were conducted at different temperature differences for samples with different thicknesses and contact areas. The measurement results for PZT M202 (427 ± 1 μC m–2 K–1) are close to the datasheet value, which is 430 μC m–2 K–1. An average pyroelectric coefficient of 306 ± 2 μC m–2 K–1) is measured for the single crystal of TGS over multiple trials. The measurement results depend on the quality of the crystal and the process for the preparation of the sample. The results show internal consistency between the measurements, which are also in agreement with literature values.

Coupled magnetic and ferroelectric states in the distorted honeycomb system Fe4Ta2O9

We report on the magnetic, thermodynamic, dielectric, and pyroelectric measurements on the hitherto unreported Fe${_4}$Ta${_2}$O${_9}$. This system is seen to exhibit a series of magnetic transitions, many of which are coupled to the emergence of ferroelectric order, making Fe${_4}$Ta${_2}$O${_9}$ the only genuine multiferroic in its material class. We suggest that the observed properties arise as a consequence of an effective reduction in the dimensionality of the magnetic lattice, with the magnetically active Fe${^{2+}}$ ions preferentially occupying a quasi 2D buckled honeycomb structure. The low temperature $H$-$T$ phase diagram of Fe${_4}$Ta${_2}$O${_9}$ reveals a rich variety of coupled magnetic and ferroelectric phases, in similarity with that observed in the distorted Kagome systems.

Microstructure and Electrical Transport Properties of Bi3TiNbO9 High-Temperature Piezoceramics

High-density ceramic samples of the Bi3TiNbO9 ferroelectric phase with a layered perovskite-like structure have been produced by tape casting slurry technology and hot pressing processes. The samples have been characterized by X-ray diffraction and dielectric, piezoelectric, and pyroelectric measurements. The results demonstrate that the samples have a well-defined texture due to the preferential orientation of the basal planes of their platelike grains across the pressing axis or along the film casting direction. The Curie temperature of the samples has been determined to be TC = 1180 K. The samples have anisotropic electrical transport characteristics. Their piezoelectric constants d33 in directions perpendicular and parallel to the texture plane is 22 and 5 pC/N, respectively. The conclusion has been drawn that the synthesized materials are potentially attractive for producing high-temperature piezoelectric elements.

Structural and magnetic phase transitions in Cs2[FeCl5(H2O)

The compound is magnetoelectric but not multiferroic with an erythrosiderite-related structure. We present a comprehensive investigation of its structural and antiferromagnetic phase transitions by polarization microscopy, pyroelectric measurements, x-ray diffraction and neutron diffraction. At about K, the compound changes its symmetry from Cmcm to I2/c, with a doubling of the original c-axis. This transformation is associated with rotations of the octahedra and corresponds to an ordering of the molecules and of the related bonds. A significant ferroelectric polarization can be excluded for this transition by precise pyrocurrent measurements. The antiferromagnetic phase transition occurring at results in the magnetic space group , which perfectly agrees with previous measurements of the linear magnetoelectric effect and magnetization.

Nonswitchable polarization and magnetoelectric coupling in the high-pressure synthesized doubly ordered perovskites NaYMnWO6 and NaHoCoWO6

The doubly ordered perovskites $\mathrm{Na}Ln\mathrm{MnW}{\mathrm{O}}_{6}$ ($Ln=\mathrm{La}$, Nd, and Tb), $\mathrm{Na}Ln\mathrm{FeW}{\mathrm{O}}_{6}$ ($Ln=\mathrm{La}$ and Nd), and $\mathrm{Na}Ln\mathrm{CoW}{\mathrm{O}}_{6}$ ($Ln=\mathrm{Sm}\ensuremath{-}\mathrm{Er}$, Yb, and Y) have been reported to be potential multiferroics because of their polar crystal structure ($P{2}_{1}$) and antiferromagnetic ordering of the transition-metal ions at low temperatures. In these materials, the octahedral rotation resulting from the layered ordering of cations at the $A$-site and the rock-salt ordering of cations at the $B$-site is suggested to be responsible for ferroelectric polarization. However, the ferroelectricity of these compounds has never been confirmed experimentally. Here we report an experimental demonstration of nonswitchable electric polarization below the magnetic ordering temperatures in two representative compounds, namely $\mathrm{NaYMnW}{\mathrm{O}}_{6}$ and $\mathrm{NaHoCoW}{\mathrm{O}}_{6},$ with smaller $Ln$-ions synthesized by high pressure and high temperatures. These compounds crystallize in the polar structure ($P{2}_{1}$) and undergo antiferromagnetic ordering at ${T}_{\mathrm{N}}\ensuremath{\sim}9\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, where a dielectric anomaly occurs in zero magnetic field. While the conventional $P\ensuremath{-}E$ loop measurements suggest the absence of ferroelectric polarization in the paramagnetic state, the pyroelectric current measurements across the magnetic ordering temperature show a nonswitchable change in polarization ($\mathrm{\ensuremath{\Delta}}P$) at ${T}_{\mathrm{N}}$, indicating a large energy barrier between the two polar states. The change in polarization at $Tl{T}_{\mathrm{N}}$ under magnetic field reveals magnetoelectric coupling.

Polar Imperfections in Amino Acid Crystals: Design, Structure, and Emerging Functionalities.

Crystals are physical arrays delineated by polar surfaces and often contain imperfections of a polar nature. Understanding the structure of such defects on the molecular level is of topical importance since they strongly affect the macroscopic properties of materials. Moreover, polar imperfections in crystals can be created intentionally and specifically designed by doping nonpolar crystals with "tailor-made" additives as dopants, since their incorporation generally takes place in a polar mode. Insertion of dopants also induces a polar deformation of neighboring host molecules, resulting in the creation of polar domains within the crystals. The contribution of the distorted host molecules to the polarity of such domains should be substantial, particularly in crystals composed of molecules with large dipole moments, such as the zwitterionic amino acids, which possess dipole moments as high as ∼14 D. Polar materials are pyroelectric, i.e., they generate surface charge as a result of temperature change. With the application of recent very sensitive instruments for measuring electric currents, coupled with theoretical computations, it has become possible to determine the structure of polar imperfections, including surfaces, at a molecular level. The detection of pyroelectricity requires attachment of electrodes, which might induce various artifacts and modify the surface of the crystal. Therefore, a new method for contactless pyroelectric measurement using X-ray photoelectron spectroscopy was developed and compared to the traditional periodic temperature change technique. Here we describe the molecular-level determination of the structure of imperfections of different natures in molecular crystals and how they affect the macroscopic properties of the crystals, with the following specific examples: (i) Experimental support for the nonclassical crystal growth mechanism as provided by the detection of pyroelectricity from near-surface solvated polar layers present at different faces of nonpolar amino acid crystals. (ii) Enantiomeric disorder in dl-alanine crystals disclosed by detection of anomalously strong pyroelectricity along their nonpolar directions. The presence of such disorder, which is not revealed by accurate diffraction techniques, explains the riddle of their needlelike morphology. (iii) The design of mixed polar crystals of l-asparagine·H2O/l-aspartic acid with controlled degrees of polarity, as determined by pyroelectricity and X-ray diffraction, and their use in mechanistic studies of electrofreezing of supercooled water. (iv) Pyroelectricity coupled with dispersion-corrected density functional theory calculations and molecular dynamics simulations as an analytical method for the molecular-level determination of the structure of polar domains created by doping of α-glycine crystals with different l-amino acids at concentrations below 0.5%. (v) Selective insertion of minute amounts of alcohols within the bulk of α-glycine crystals, elucidating their role as inducers of the metastable β-glycine polymorph. In conclusion, the various examples demonstrate that although these imperfections are present in minute amounts, they can be detected by the sensitive pyroelectric measurement, and by combining them with theoretical computations one can elucidate their diverse emerging functionalities.

Pyroelectric energy conversion with large energy and power density in relaxor ferroelectric thin films.

The need for efficient energy utilization is driving research into ways to harvest ubiquitous waste heat. Here, we explore pyroelectric energy conversion from low-grade thermal sources that exploits strong field- and temperature-induced polarization susceptibilities in the relaxor ferroelectric 0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3. Electric-field-driven enhancement of the pyroelectric response (as large as -550 μC m-2 K-1) and suppression of the dielectric response (by 72%) yield substantial figures of merit for pyroelectric energy conversion. Field- and temperature-dependent pyroelectric measurements highlight the role of polarization rotation and field-induced polarization in mediating these effects. Solid-state, thin-film devices that convert low-grade heat into electrical energy are demonstrated using pyroelectric Ericsson cycles, and optimized to yield maximum energy density, power density and efficiency of 1.06 J cm-3, 526 W cm-3 and 19% of Carnot, respectively; the highest values reported to date and equivalent to the performance of a thermoelectric with an effective ZT ≈ 1.16 for a temperature change of 10 K. Our findings suggest that pyroelectric devices may be competitive with thermoelectric devices for low-grade thermal harvesting.

Solvent‐Induced Crystal Polymorphism as Studied by Pyroelectric Measurements and Impedance Spectroscopy: Alcohols as Tailor‐Made Inhibitors of α‐Glycine

AbstractMetastable polymorphs commonly emerge when the formation of the stable analogues is inhibited by using different solvents or auxiliaries. Herein, we report that when glycine is grown in aqueous solutions in the presence of low concentrations of different co‐solvents, only alcohols and acetone, unlike water and acetic acid, are selectively incorporated in minute amounts within the bulk of the α‐polymorph. These findings demonstrate that although water binds more strongly to the growing face of the crystal, alcohols and acetone are exclusively incorporated, and thus serve as efficient inhibitors of this polymorph, leading to the precipitation of the β‐form. These solvents then create polar domains detectable by pyroelectric measurements and impedance spectroscopy. These results suggest that in the control of crystal polymorphism with co‐solvents, one should consider also the different desolvation rates in addition to the energy of binding to the growing faces of the crystal.

Solvent-Induced Crystal Polymorphism as Studied by Pyroelectric Measurements and Impedance Spectroscopy: Alcohols as Tailor-Made Inhibitors of α-Glycine.

Metastable polymorphs commonly emerge when the formation of the stable analogues is inhibited by using different solvents or auxiliaries. Herein, we report that when glycine is grown in aqueous solutions in the presence of low concentrations of different co-solvents, only alcohols and acetone, unlike water and acetic acid, are selectively incorporated in minute amounts within the bulk of the α-polymorph. These findings demonstrate that although water binds more strongly to the growing face of the crystal, alcohols and acetone are exclusively incorporated, and thus serve as efficient inhibitors of this polymorph, leading to the precipitation of the β-form. These solvents then create polar domains detectable by pyroelectric measurements and impedance spectroscopy. These results suggest that in the control of crystal polymorphism with co-solvents, one should consider also the different desolvation rates in addition to the energy of binding to the growing faces of the crystal.

Innenrücktitelbild: Solvent‐Induced Crystal Polymorphism as Studied by Pyroelectric Measurements and Impedance Spectroscopy: Alcohols as Tailor‐Made Inhibitors of α‐Glycine (Angew. Chem. 18/2018)

Innenrücktitelbild: Solvent‐Induced Crystal Polymorphism as Studied by Pyroelectric Measurements and Impedance Spectroscopy: Alcohols as Tailor‐Made Inhibitors of α‐Glycine (Angew. Chem. 18/2018)

Inside Back Cover: Solvent‐Induced Crystal Polymorphism as Studied by Pyroelectric Measurements and Impedance Spectroscopy: Alcohols as Tailor‐Made Inhibitors of α‐Glycine (Angew. Chem. Int. Ed. 18/2018)

Inside Back Cover: Solvent‐Induced Crystal Polymorphism as Studied by Pyroelectric Measurements and Impedance Spectroscopy: Alcohols as Tailor‐Made Inhibitors of α‐Glycine (Angew. Chem. Int. Ed. 18/2018)

Synthesis, X-ray Diffraction Characterization, Mössbauer Spectroscopy, and Dielectric Properties of Solid Solutions in the PbFe2/3W1/3O3–PbSc2/3W1/3O3 System

Ceramic Pb(Fe1–xSc x )2/3W1/3O3 samples with 0 ≤ x ≤ 1 have been prepared and characterized by X-ray diffraction, Mossbauer spectroscopy, and dielectric and pyroelectric measurements. The stoichiometry ranges of the perovskite solid solutions in this system have been identified, their structural parameters have been determined, and their dielectric permittivity, dielectric loss tangent, resistivity, and thermally stimulated depolarization current have been measured as functions of temperature. The composition dependences of the dielectric properties for the solid solutions have been obtained. The solid solutions have been shown to exhibit ferroelectric relaxor properties, with a well-defined maximum in their permittivity in the range 180–250 K.