Telluric Acid Ammonium Phosphate Research Articles

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.

Ultrasonic velocity and attenuation in ferroelectric TAAP

The longitudinal ultrasonic velocity and attenuation in ferroelectric telluric acid ammonium phosphate (TAAP) along the direction perpendicular to the (101) face has been measured across the Curie temperature at 10, 30 and 50 MHz. A pronounced anomaly in ultrasonic attenuation is observed at 50 MHz near the Curie temperature. The ultrasonic velocity exhibits a slope variation at the transition temperature.

Effect of pressure on the ferroelectric properties of telluric acid ammonium phosphate

Telluric acid ammonium phosphate (TAAP) is a new class-m ferroelectric with a transition temperature of 45 degrees C. Recent Raman spectroscopy studies of this crystal suggest that the phase transition takes place predominantly by the order-disorder nature of the hydrogen bonds of the type N-H-O. The hydrogen-bonded ferroelectrics are known to be very sensitive to external pressure and deuteration. In view of this, the effect of hydrostatic pressure on ferroelectric properties of TAAP has been studied up to 6 kbar. It was found that Tc shifts to lower temperatures under the influence of external pressure. At low pressures, Tc decreases more rapidly than at high pressures. The pressure derivative evaluated from the linear portion of the curve is -2.69 degrees C kbar-1. The effect of pressure on the spontaneous polarisation is to reduce its value although the continuous nature of the transition does not undergo any change up to the maximum pressure employed. These results and the shift of Tc to higher temperature upon deuteration support the order-disorder nature of the hydrogen bonds during the phase transition.

Polarization reversal studies in ferroelectric taap

Abstract Telluric Acid Ammonium Phosphate (Te(OH)62(NH4)H2PO4(NH4)2HPO4) reffered to as TAAP is a recently discovered class m ferroelectric.1 It undergoes FE-PE transition at 48°C. Switching studies in this crystal has been carried out in the temperature range −14°C to 39°C by applying fields up to 4 kV/cm. Measurements were carried out on (101) plates cut from the crystals grown from solution. X-ray irradiation was carried out at room temperature by means of an x-ray tube operating at 25 kV and 15 mA with copper target. Air drying silver paste was used as electrodes. Samples were checked for hysteresis loop using a modified Sawyer-Tower circuit. The P s value obtained from the loop is 2.1 μC/cm2 which is comparable to the earlier reported value. It was however noticed that the loop was slightly shifted to right with respect to the origin indicating the presence of a small internal bias which was 100 V/cm in the virgin crystal. This bias could not be removed even after repeated crystallization. On irradia...

Elastic properties of monoclinic telluric acid ammonium phosphate, Te(OH)6�2NH4H2PO4�(NH4)2HPO4, near the paraelectric-ferroelectric transition

The elastic constants of Te(OH)6·2NH4H2PO4·(NH4)2HPO4, TAAP, point symmetrym, have been measured by ultrasonic resonance methods passing through the paraelectric-ferroelectric transition at ca. 320 K. In the range between 273 and 340 K the elasticity tensor exhibits only a slight anisotropy. No discontinuity of the elastic constants is observed. However, some temperature derivatives of the elastic constants show slight anomalies within the range 310 to 325 K. The strongest effect occurs with the longitudinal elastic resistancec22. The thermal expansion which varies only slightly between 263 and 340 K, is highly anisotropic in contrast to the thermoelastic behaviour. A strong negative thermal expansion is observed in a direction within the mirror plane, ca. 45° apart from the direction of spontaneous polarization.

Monoclinic telluric acid ammonium phosphate (TAAP) A new ferroelectric compound iii dielectric and related properties

Monoclinic telluric acid ammonium phosphate (TAAP) is shown to be a new class m ferroelectric with a Curie temperature close to ambient (48°C). Emphasis is placed on dielectric and thermal properties, but some optical results are also reported. The material behaves closely like TGS and, from a practical point of view, could be useful in pyroelectric applications.