Telluric Acid Ammonium Phosphate Crystals 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.

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.

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.

Influence of temperature variations on the visualisation of the ferroelectric domains of TGS and TAAP crystals by scanning electron microscopy

Abstract Temperature variations of aged Triglycine Sulphate (TGS) and Telluric Acid Ammonium Phosphate (TAAP) samples increase the contrast between positive and negative ends of domains observed with a scanning electron microscope. For freshly cleaved surface of TGS, an increase of temperature of 2°C inverts the contrast between these domains. When the temperature of the TGS samples increases continuously, we observe a deformation of the picture on the screen, but it is not observed for TAAP samples. Thermally stimulated electron emission is also observed and measured. These phenomena are due to the surface charges produced by the modification of the spontaneous electric polarization of the samples when the temperature varies.

Microwave dielectric dispersion in ferroelectric telluric acid ammonium phosphate

Abstract The paper presents the results of the investigation of dielectric dispersion in monoclinic telluric acid ammonium phosphate crystal over the frequency range 1 MHz to 77 GHz. It is shown that ferroelectric dispersion of the Debye type along the direction perpendicular to the plane (101) occurs in the frequency range 108 to 1011 Hz and is caused by a single relaxational soft mode. The relaxational soft mode is caused by the flipping motion of protons between two potential minima in a hydrogen bond. The frequency of the flipping proton mode in the paraelectric phase varies according to vs = 0.94 (T – To ) GHz and decreases to 1.75 GHz at Tc = 317.3 K. The relaxational mode gives the main contribution to the high static dielectric permittivity of this crystal which fits the Curie-Weiss law. The results confirm the order-disorder nature of a proper ferroelectric phase transition of second order.