Telluric Acid Ammonium Phosphate Research Articles

Domain switching in TAAP crystal in the vicinity of phase transition

The field-dependent domain structure was investigated in non-uniform telluric acid ammonium phosphate (TAAP) crystal by direct imaging of a domain structure by means of nematic liquid crystal method. Micro-scale studies of domain switching in conjunction with measurements of switching currents enable us to establish a relationship between local properties of domain dynamics and macroscopic response of the switched polarization. We present experimental results showing that defects in TAAP crystal may strongly influence the dynamics and distribution of the domain walls in the vicinity of phase transition, giving rise to the distribution of transition temperatures in the local regions of TAAP crystal.

Equation of State for Pressure and Temperature Induced Transitions in Uniaxial Ferroelectrics TAAP and TGSe

Experimental investigations of phase transitions induced by temperature and by pressure in uniaxial ferroelectrics: TAAP, (telluric acid ammonium phosphate), with ordinary critical point and TGSe, (triglycine selenate), which shows a quasi-tricritical point, have been performed. The combined pressure and temperature dependences of polarization versus electric field are shown to scale well using the generalized scaling variable [1−(T/TC + p/pC)] which involves temperature (T) and pressure (p), being TC the transition temperature at zero pressure and pC, the transition pressure at zero absolute temperature.

Dynamics of the domain structure in non-uniform ferroelectric crystals

This work presents a study of the domain reversal characteristics related to the internal bias field in nonuniform telluric acid ammonium phosphate (TAAP) crystal. We have shown that there is a direct connection between the defective structure of the crystal and stretched exponential polarization relaxation in ferroelectric crystals. The domain switching was studied by means of the nematic liquid crystal decoration technique.

Effect of internal bias field on the polarization reversal in non-uniform telluric acid ammonium phosphate (TAAP) ferroelectric crystal

The mechanism of polarization reversal in non-uniform telluric acid ammonium phosphate (TAAP) ferroelectric crystal has been found to be strongly influenced by an internal bias field distribution. It was shown that the internal bias field, originated from some structural defects can stabilize local domain structures, causing its fast spontaneous return to the original state. To reveal the effect of E b on the domain motion, measurements of the distribution of domain wall velocity during switching and spontaneous backswitching processes have been performed. A qualitative approach was proposed in order to find a distribution of the E b in the crystal.

Deuteration Effect on the Ferroelectric Phase Transition of TAAP

Partially deuterated telluric acid ammonium phosphate (TAAP) single crystals were grown from water solutions with various H 2 O and D 2 O ratios. The transition temperature T C was determined from the dielectric anomaly characteristic to the second order phase transition. Deuteration molar fraction x c in the crystal was determined by a mass spectrograph. It was proved that T C increases almost linearly with x c . The maximum transition temperature reached 357 K for x c = 0.73. The deuteration effect in TAAP is clearly smaller than that in the typical hydrogen-bonded ferroelectrics such as KDP-type but considerably larger than TGS-type ferroelectrics.

Slow polarization relaxation in non-uniform telluric acid ammonium phosphatecrystals

The characteristic features of polarization and spontaneous depolarization kinetics innon-uniform telluric acid ammonium phosphate (TAAP) crystals are investigated byobservation of the domain structure using a nematic liquid crystal method. We presentexperimental results showing the correlation between the internal bias field, responsible forthe offset of the hysteresis loop and the backswitching process. The internal fieldcaused by structural disorder accounts for a broad spectrum of energy barriers fordomain nucleation. The switching kinetics was analysed in the framework of thenucleation and growth model based on Avrami statistical theory, using the modifiedKolmogorov–Avrami–Ishibashi (KAI) model. It has been found that the switching kineticsin TAAP crystals can be approximated by averaging the KAI model over a broaddistribution of characteristic domain growth times. The spectra of the distribution ofthe characteristic domain growth times are derived from the experimental data.

Polarization reversal of telluric acid ammonium phosphate

Experimental studies are reported concerning polarization reversal in the single crystal of telluric acid ammonium phosphate (TAAP). The switching currents have been measured under various temperatures and external electric fields. The experimental results have been used in order to obtain the effective growth dimension of reversed domain and the characteristic time of the polarization reversal on the basis of the Avrami theory. It becomes clear that the effective growth dimension depends on temperature and applied electric field.

Influence of temperature on the depolarization process in telluric acid ammonium phosphate crystal

This work presents a study of the domain reversal characteristics such as switching time and threshold coercive fields for domain reversal related to the internal bias field and its dependence on temperature. The results are presented for unipolar telluric acid ammonium phosphate crystal in which stabilization of a spontaneous polarization is so strong that depolarization of the crystal occurs after removing of the poling field. The domain structure dynamics was studied by nematic liquid crystal method.

Effect of internal bias field on 180° domain switching in telluric acid ammonium phosphate crystal

The depolarization effect in a telluric acid ammonium phosphate crystal has been studied by direct imaging of the domain structure by nematic liquid-crystal decoration technique. The stabilization mechanism of 180° domains appears to have a correlation to a defect—induced internal field in the crystal. The internal field acts as a driving field causing nucleation and growth of domains. The strong effect of the poling voltage parameters (duration and amplitude) on the depolarization process is reported.

Temperature Dependence of Switching Process in Telluric Acid Ammonium Phosphate (TAAP) Crystals

Direct observation of the switching process in telluric acid ammonium phosphate crystals at different temperatures was carried out using nematic liquid crystal (NLC) decoration technique. The switching of TAAP crystals can be described as thermally activated process and the switching time t s obeys the Arrhenius law t s =t 0 exp(W/kT). The temperature dependence of switching time indicates that there exists in TAAP different groups of nucleation centres with different activation energies W.

Temperature Dependence of Switching Process in Telluric Acid Ammonium Phosphate (TAAP) Crystals

Direct observation of the switching process in telluric acid ammonium phosphate crystals at different temperatures was carried out using nematic liquid crystal (NLC) decoration technique. The switching of TAAP crystals can be described as thermally activated process and the switching time t s obeys the Arrhenius law t s =t 0 exp(W/kT). The temperature dependence of switching time indicates that there exists in TAAP different groups of nucleation centres with different activation energies W.

Switching kinetics of 180° domains in telluric acid ammonium phosphate crystals with large unipolarity

The switching process in unipolar telluric acid ammonium phosphate crystal has been studied by a combination of optical observation of the domain structure in low electric fields and electrical switching measurements in high fields. The stabilization mechanism of 180° domains appears to have a correlation to a defect-induced internal field Eb in the crystal. In crystal sample with Eb>Ec (Ec, coercive field measured from D–E hysteresis loop), the spontaneous repolarization of the crystal occurs after the removal of the applied field. It has been found that Eb acts as a driving field causing nucleation and growth of back-switching domains.

Ferroelectric polarization reversal in telluric acid ammonium phosphate crystals

Switching process in TAAP crystals has been studied by optical observation of the domain structure in low electric fields and switching current registration in high electric fields. The relationship between the growth of reversed domains and switching current as well as switching time has been discussed.

Domain Pattern Evolution in Polarization Reversal of Telluric Acid Ammonium Phosphate Crystals

Telluric acid ammonium phosphate (TAAP) having the chemical formula Te(OH)6 • 2NH4H2PO 4 • (NH4)2HPO4 undergoes the phase transition at 321 K changing its symmetry from the centrosymmetric class 2/m to the polar class m [1]. Currently most of what is known about the TAAP crystals relates to dielectric properties, little is known about their domain kinetics. The static domain structure has been observed by the etching technique [2]. This method simultaneously reveals the dislocations and other lattice imperfections. The first switching current measurement of ferroelectric polarization reversal in TAAP has been reported in Ref. [3]. Here we communicate the peculiarities of the domain structure dynamics in the TAAP crystals at room temperature.

Ferroelectric specific heat of telluric acid ammonium phosphate single crystal near T c

Precise specific heat data on good quality Telluric Acid Ammonium Phosphate (TAAP) have been obtained in the vicinity of the ferroelectric-paraelectric phase transition ( T c ≈ 44.8 °C). The experimental specific heat discontinuity at T c, ΔC P exp( T c) = 0.085J/gK, is somewhat lower than the expected value, Δ C P cal( T c) = 3/2 Nk B(1 − 3 g) −1 ϱ −1 = 0.129J/gK, with g = 0.28 determined from spontaneous polarization Ps( T). Using a linear background interpolation for the non-ferroelectric contributions to the specific heat, we get Δ S exp( T c) = 5.25 × 10 −3J/gK<Nk Bϱ −1 Ln2 = 9.65 × 10 −3J/gK (transition entropy), and Δ Q exp( T c) = 1.608J/g<1/2 Nk B T cϱ −1 = 2.214J/g (transition heat).

Equation of state for the pressure- and temperature-induced transition in ferroelectric telluric acid ammonium phosphate

A careful experimental investigation of the ferroelectric-paraelectric transition in uniaxial ferroelectric telluric acid ammonium phosphate induced by pressure and by temperature in the vicinity of the phase transition has been carried out. Dielectric-constant and hysteresis-loop data allow the determination of the combined equation of state as a function of both temperature and pressure, relating accurately polarization, field, pressure, and temperature in the neighborhood of the transition.

Phonon assisted electronic transition in telluric acid ammonium phosphate single crystals

Abstract The effect of gamma-irradiation on the absorption optical spectra of telluric acid ammonium phosphate single crystals (TAAP) has been studied, in the wave length of 200–600 nm, for samples irradiated by various doses up to 10 Mrad. The results show that the electron phonon coupling constant increases with the irradiation dose.

Ferroelectric behavior of TAAP single crystal near Tc

Abstract Dielectric and hysteresis loop measurements in good quality telluric acid ammonium phosphate from 20 to 50°C with special attention to the behavior in the vicinity of Tc ≍ 44.80 °C were performed. The effective field higher order parameters characterizing the temperature dependence of the spontaneous polarization were obtained. The main features of the ferroelectric transition in this “hard” ferroelectric have been compared with those of other well known ferroelectric crystals.

Field-induced electron emission of telluric acid ammonium phosphate

Abstract Investigations of the field-induced electron emission from ferroelectric telluric acid ammonium phosphate (TAAP) crystals have been carried out. The influence of the emitting surface (free or partly electroded) and internal bias on electron emission processes occuring at TAAP sample surface, in the vicinity of the phase transition temperature, are reported. The results obtained are discussed.

Anomalous behaviour of linear birefringence and strain in taap crystal

Abstract Linear birefringence and lattice parameters were measured for the ferroelectric telluric acid ammonium phosphate in the temperature range 200–340 K. It is shown that anomalous temperature behaviour of the linear birefringence increment δ(Δn1) induced by the ferroelectric phase transition can be attributed to the temperature change of the spontaneous strain e13.