Pyroelectric Current Measurements Research Articles

Second Harmonic Generation from Multiferroic MnWO4

Ferroelectric polarization induced by spin ordering is of current interest, and various compounds exhibiting simultaneous magnetic and ferroelectric phase transitions, called ‘‘multiferroics’’, have been experimentally studied extensively. In most of these studies, pyroelectric-current measurement has been employed to confirm the existence of ferroelectric polarization. However, this measurement can be performed only after a large electric field is applied to the sample for the purpose of aligning ferroelectric domains, and thus, cannot be regarded as the detection of purely spontaneous polarization in a ferroelectric phase. One of the experimental techniques for detecting ferroelectric polarization without aligning ferroelectric domains is second harmonic generation (SHG). SHG is absent from crystals with inversion symmetry, and thus, the detection of the SH signal in multiferroics gives important information on their ferroelectric polarization. The sample investigated in this study is MnWO4. This compound exhibits three different magnetic phases below TN 1⁄4 13:5K, T2 1⁄4 12:7K, and T1 1⁄4 7:6K, and the elliptical spiral spin phase in the intermediate temperature range (T1 < T < T2) was found to show ferroelectric polarization by pyroelectric-current measuement. One of the advantages of studying MnWO4 for SHG is that MnWO4 is optically transparent for the incident light ( 1064 nm) of the SH measurement. Since most multiferroics are opaque at all photon energies, the SH signal can be detected only in the reflection configuration, but this gives a fairly weak SH signal, which is difficult to distinguish from the SHG induced by inversion-symmetry breaking at the sample surface. Using transparent MnWO4, we can detect the SH signal in the transmittance configuration. A single crystal of MnWO4 was grown by the floatingzone method. The sample was easily cleaved along the ac-plane. We checked the sample quality by X-ray Laue reflection analysis and dielectricand pyroelectric-current measurements. The results were consistent with those reported in ref. 5. The 1064 nm light from a Nd:YAG laser (5 ns pulse width, 1mJ pulse energy, and 9Hz repetition) was used as incident light and focused onto the sample with a 1mm spot, and 532 nm light from the sample was detected by a liquid-N2-cooled CCD detector with appropriate optical filters and a grating spectrometer to eliminate stray light. Although the incident light can penetrate into the sample at sufficiently long distance, a small absorption of the incident light causes serious heating of the sample for low-temperature measurement, and thus, the thickness of the sample has to be as small as possible to minimize such absorption. We were able to obtain such a thin sample only by cleaving the crystal along the ac-plane. On the other hand, ferroelectric polarization is expected along the b-axis from the pyroelectric current measurement, Thus, we set the cleaved sample whose b axis (normal to the sample surface) is canted from the laser beam by 30 so that the electric-field vector of the incident light contains a finite b-component. In this polarization configuration, SHG with any third-order tensors is involved in the emitted light. The sample was cooled by a liquid-He-flow cryostat. We also measured the absorption spectrum of the sample between 0.6 and 3 eV at room temperature. Figure 1 shows the absorption spectrum of MnWO4 with the polarization direction along the ac-plane. The increase in absorption coefficient above 2.4 eV corresponds to the onset of an interatomic absorption, presumably between the O 2p level and the Mn 3d level. The small peak at 2.2 eV corresponds to an intraatomic transition within the Mn2þ ion (3d), i.e., a spin-forbidden transition of an electron from the eg orbital to the t2g orbital. 6) In our experiment on SHG, the energy of incident light (1064 nm, 1.16 eV) is far below the absorption edge and the intraatomic absorption, but the SH light (532 nm, 2.33 eV) is on the intraatomic absorption of Mn2þ. Since this absorption is fairly weak, the optical transmittance of the sample with a 0.11mm thickness used for the SHG measurement amounts to 30% at 532 nm. Figure 2 shows the spectrum of the light emitted from the sample when an incident 1064 nm laser was applied. There is a peak at around 532 nm, which indicates the emission of SH light. The fine structures of the peak are due to the irregular shape of the laser spot in real space (caused by the roughness of the cleaved surface) and a wide-open slit of the spectrometer immediately before the CCD camera (wider than the laser spot). As can be seen, the peak is enhanced at 10 and 8K. Figure 3 shows the temperature dependence of the integrated intensity of the peak at around 532 nm, 1 2 0 200 400

Dielectric Characteristics of Perovskite‐Structured High‐Temperature Relaxor Ferroelectrics: The BiScO3–Pb(Mg1/3Nb2/3)O3–PbTiO3 Ternary System

A new compositional family of relaxor ferroelectrics was investigated based on the high‐temperature Bi(Me)O3–PbTiO3 ferroelectric perovskite family. Compositions were fabricated near an estimated morphotropic phase boundary (MPB) of the xBiScO3–yPb(Mg1/3Nb2/3)O3–zPbTiO3 (xBS–yPMN–zPT) ternary system exhibiting high‐temperature relaxor properties of Tmax∼250°–350°C and ɛmax∼10 000–24 000 at 1 kHz. Analysis of the low‐field a.c. permittivity by a Vogel–Fulcher type dependence enabled key parameters of activation energy, EA, and freezing temperature, Tf, to be determined. The remanent polarization was studied over a broad temperature range and was observed to show classical ferroelectric square loop hysteresis behavior at temperatures T&lt;Tf while slim loop hysteresis behavior was observed at temperatures Tf&lt;T&lt;Tmax. Pyroelectric current measurements were made and integrated to determine macroscopic polarization‐temperature dependence, and were in excellent agreement with the hysteresis data. The macroscopic polarization was found to drop off rapidly near the freezing temperature, Tf. At temperatures T&gt;Tmax, the deviation temperature, TD, was obtained from Curie–Weiss analysis and found to be ∼600°C. A comparison of characteristic electrical properties was made between the high‐temperature perovskite relaxors and the classical complex lead relaxor compound, Pb(Mg1/3Nb2/3)O3 (PMN).

Ferroelectricity from Valence Ordering in RFe2O4

We report a polar ordering of electrons in RFe 2 O 4 , which consistently explains the ferroelectric property of this material. Pyroelectric current measurement, low frequency AC dielectric constants, resonant X-ray scattering diffraction experiment and the consideration for the charge frustration, consistently lead the presence of ferroelectricity originated from the ordering of Fe 3+ and Fe 2+ . The ferroelectric material originated from the polar electron distribution and free from the ionic displacement may potentially have great possibilities in future applications and fundamental researches.

Poling of soft piezoceramic PZT

The properties of piezoelectric ceramic materials are strongly dependent on the degree of polarization as set by the poling process. In the present work a soft piezoceramic PZT material was polarized at different poling conditions. The hysteresis loop, the polarization current and pyroelectric current measurements were used to evaluate the polarization state of the material. The hysteresis loop was monitored using a home-made computer controlled Sawyer–Tower circuit. The polarization current was recorded during the poling process at different applied electric fields, poling time and temperature. The pyroelectric coefficient and the polarization were calculated from the pyroelectric current. The polarization calculated from these data was in excellent agreement with the polarization as calculated from the poling current. The relative permittivity and loss factor were measured as a function of temperature after different poling conditions. The effects of the various poling conditions on the dielectric and ferroelectric properties of the soft PZT are discussed. It is shown that, contrary to common practice, poling at a field slightly larger than the coercive field is adequate to reach full polarization at room temperature.

Pyroelectric and piezoelectric properties of thick PZT films produced by a new sol–gel route

The pyroelectric and piezoelectric properties of thick PZT films processed via a new sol–gel method are being investigated. The films were deposited on gold-coated alumina substrates. The pyroelectric properties are being evaluated using pyrodynamic measurements with either a laser or thermoelectric heat source. The pyroelectric coefficient is obtained from pyroelectric current measurements. The piezoelectric properties are being measured using a laser vibrometer-lock-in amplifier set-up. It is shown that the pyroelectric coefficient obtained with laser heating lies in the range of 108 μC/m 2 K, whereas heating from the rear of the specimen with the thermoelectric element lead to a value of in the range of 350 μC/m 2 K. These results are explained in terms through thickness temperature gradients. The piezoelectric displacement amplitude versus applied voltage shows a no-linear behaviour, which is explained in terms of materials chemistry. The maximum effective piezoelectric coefficient, d 33, is obtained as 340 pm/V, and is superior to the values known for ferroelectric thin films.

Pyroelectric Electron Emission Behaviors of Congruent and Stoichiometric Lithium Niobate Single Crystals

Pyroelectric electron emission current measurements and current distribution collecting were performed on congruent and stoichiometric lithium niobate single crystals. Electron emission behaviors were found to be gap distance (crystal-detector) dependent. For small gaps, in both crystal compositions, emission was accompanied by a partial superficial domain inversion, triggered by surface plasma ignition. For large gaps (> 2 mm) in congruent single crystals the emission was activated by a true pyroelectric effect.

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.

Temperature Dependence of the Order Parameter in Ferroelectric LiTaO3

Accurate measurements of birefringence in LiTaO3:Cr+ single crystals in the interval 100 K ≤ T ≤ 1000 K have been performed. The temperature dependence of the order parameter, the square root of the birefringence change, has been shown to produce a clear second order ferroelectric phase transition in this distorted perovskite. The results are compared with those obtained for spontaneous polarization from pyroelectric current measurements.

Study of the pyroelectricity in LiIns 2 crystal

Pyroelectric current measurements performed on a LiInS 2 monodomain single crystal show a linear variation of the current between 120 and 260 K. Near room temperature, a space charge relaxation screens pyroelectricity. The pyroelectric coefficient follows a linear thermal dependence leading to an extrapolated value of 6×10 −10 C K −1 cm −2 at 300 K. As for other oxide-type pyroelectric compounds, this value is shown to be proportional to the electro-optic coefficient r 333 of LiInS 2.

Ergodicity breaking in stronium calcium titanate

This work reports experimental results obtained from series of measurements ofpyroelectric currents in samples of strontium calcium titanate (SCT)corresponding to contents of Ca of x = 0.002, x = 0.005 and x = 0.011.Sequences of zero field cooling (zfc), field heating (fh), field cooling (fc)and zero field heating (zfh) runs, under different applied electric fields,allowed the observation of the temperature and field dependence of theelectric polarization under different initial conditions. The results show theexistence of a weak non-ergodic regime in the compositions x = 0.005 andx = 0.011 and allow the tracing of the corresponding Almeida-Thouless line inthe T-E diagram. For the three compositions investigated, a small zerofield polarization is detected and interpreted as due to defect inducedinternal fields.

Elastic neutron scattering and dielectric behaviour of 4% brominated betaine calcium chloride dihydrate (BCCD)

We report a combined experimental study by means of elastic neutron scattering and dielectric measurements of a partially deuterated and x =4% brominated BCCD (Betaine Calcium Chloride Dihydrate) crystal. The lowest-temperature phase is one-dimensional modulated and characterized by the coexistence of different commensurate domains (with ∂ = 1/4, 4/17, 2/9 and 1/5 on cooling), but with a clear predominance of the five-fold phase. A huge global thermal hysteresis of the wave-vector of the modulation, attaining values of about 9 K in the incommensurate phase and up to 15 K in the “harmless” low temperature part of the phase diagram, is observed up to Ti. The role of lattice defects on this phenomenon is discussed. Similarly to the behaviour of the pure compound, the structural modulation evolves on cooling towards a soliton regime (growth of third and fifth-order satellite peaks), probably with respect to a non-stabilized non-modulated ferroelectric phase. The critical temperatures deduced from dielectric constant and pyroelectric current measurements are in very good agreement with those obtained from neutron scattering. The dielectric anomaly observed in \(\varepsilon _b^(T)\) at \(T \simeq 85\) K, and known as the “Ts-anomaly”, could not be related with any special feature detected in the neutron data, and in particular no correlation between this anomaly and the appearance of the soliton regime can be established.

Properties of PCLT/P(VDF-TrFE) 0–3 nanocomposites

Calcium and lanthanum modified lead titanate (PCLT) powder with size in the nanometer range was prepared using a sol-gel technique. PCLT powder annealed at 850°C was incorporated into a polyvinylidene fluoride/trifluoroethylene P(VDF-TrFE) copolymer matrix to form 0.15 mm thick films of 0–3 nanocomposites with ceramic volume fraction (φ) ranging from 0.05 to 0.33. The dielectric and pyroelectric properties of the composites were measured as functions of temperature. The observed permittivity and dielectric loss were found to agree with the predictions of the Bruggeman model. When the ceramic and copolymer phases in these nanocomposites are poled in the same direction, the pyroelectric activities of the two phases reinforce while the piezoelectric activities partially cancel, thereby minimizing the vibration-induced electrical noise in pyroelectric current measurements.

Polarized Raman and electrical study of single crystalline titanium modified lead magnesio-niobate

Raman scattering experiments were performed on the relaxor ferroelectric lead magnesio-niobate (PMN), the ferroelectric 0.8 PMN-0.2 (PT) and the intermediate composition 0.9 PMN-0.1 PT. In order to understand in more detail the behaviour of this series, Raman scattering spectra were also collected under dc electric field. A ferroelectric phase could be induced in the latter composition for electric fields higher than a threshold value. The behaviour of this field-induced phase was compared with the (zero-field) ferroelectric phase in 0.8 PMN-0.2 PT. Barkhausen jumps were observed in the pyroelectric current measurements, and a strong dielectric anomaly was detected in zero field heating after field cooling experiments on 0.9 PMN-0.1 PT. These results are consistent with a description of the behaviour in this series based on a cancellation of 1:1 (Mg:Nb) domain random fields by titanium ions, favouring the onset of long range ferroelectric order.

Pyroelectric effect and possible ferroelectric transition of helimagnetic and

In a series of papers, we have reported the results of dielectric, magnetic and magnetoelectric studies of (R = rare earth between Nd and Lu, Y or Bi), proposing the possibility of ferroelectricity in these oxides, but the direct demonstration of ferroelectricity was lacking. In this paper we present the results of pyroelectric current measurements of and single crystals between 4.2 and 273 K. These results indicated the existence of spontaneous polarization at low temperatures. The spontaneous polarization was switched by an applied electric field. Its possible direction is along the b axis of an orthorhombic crystal. The supposed temperature dependence of spontaneous polarization was complicated except for the case of , suggesting a ferrielectric origin of the polarization.

Pyroelectric measurements of glassy characteristics in (KDP)1−x(ADP)xsystem

Abstract Pyroelectric current measurements are applied to obtain the temperature dependence of the field-cooled polariza1, ion P FC and zero field-cooled polarization P ZFC of (KDP)1−x(ADP)x pellet samples over the whole range of x between x = 0(pure KDP) and x = 1(pure ADP). Remanent polarization P R was observed in both ferroelectric and proton glass regimes of x but not observable with s in the antiferroelectric regime. Nonergodicity, phase coexistence and diffuse phase transition characteristics seem to be well identified by the pyroelectric measurements of P FC , P ZFC and P R .

Dielectric, pyroelectric, piezoelectric and optical investigation of the phase transition sequence in BaZnGeO4

Abstract The successive phase transitions of a BaZnGeO4 crystal have been investigated by various techniques such as X-ray diffraction, DTA, dielectric, pyroelectric, piezoelectric and optical measurements from 100 K to 1300 K. The pyroelectric and optical studies have been reported for the first time in this paper. The material gives rise to a pyroelectric current from 100 K to 520 K. Five phase transitions have been detected in this temperature range by pyroelectric current measurements. The optical measurements allow the observation of four phase transitions. The birefringence decreases with rising temperature between 100 and 1300 K. A mechanism is proposed for the observed pyroelectricty.

Evidence for pyroelectricity in single variant spontaneously ordered GaInP 2

The random alloy GaInP 2 exhibits the 4 3m point group symmetry and thus does not posses a unique polar direction. In contrast, spontaneously ordered GaInP 2 exhibits the 3m point group symmetry which can give rise to pyroelectricity along the 3-fold symmetry axis or ordering direction. Due to the similarity between the Ga and In cations, any temperature variation induced polarization is expected to be very small compared with typical pyroelectrics such as hexagonal CdS. Our study yields the first experimental evidence for pyroelectricity in single variant spontaneously ordered GaInP 2. The experiments involve low frequency laser heating and pyroelectric current measurement using a lock-in detection technique.

Pyroelectric properties of ferroelectric potassium-cesium vanadate and potassium-lithium vanadate

Measurements of pyroelectric currents and coefficients of poled sintered discs of ferroelectric solid solutions, potassium-cesium vanadate and potassium-lithium vanadate have been investigated in the temperature range covering their transition points. In these solid solutions, K x Cs1−x VO3 and K x Li1−x VO3, pronounced peaks have been observed at the ferroelectric curie temperatures. The peak values of pyroelectric currents and coefficients change with change in potassium concentration in both the solid solutions.

Pyroelectric behaviour of laser-evaporated poly(vinyl fluoride) films

Laser-evaporated poly(vinyl fluoride) films were prepared with a view to their use as pyroelectric sensing elements. A high power (60 W) CO 2 laser was employed to prepare these films (0.1–1 microm thick) in a vacuum of better than 1 × 10 −5Torr. The films were characterized by determining their structure and molecular weight using IR spectroscopy and mass spectrometry. The pyroelectric currents developed in these films by poling them in electric fields of strength (1–5) × 10 5 V cm −1 and at poling temperatures of 303–450 K were measured. Various metal electrodes were used and the effect of the electrode material on the pyroelectric activity was also studied. The results are used to interpret the origin of the pyroelectricity in these films. The experimental details of the preparation of the films, their characterization and the pyroelectric current measurements are discussed.