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 10' to 10" 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 v, = 0.94 (T -To) GHz and decreases to 1.75 GHz at T, = 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.

Low Field Relaxational Behavior of Taap Single Crystal (20-106Hz)

“…Α single relaxational soft mode frequency follows the Curie-Weiss law, which confirms the order-disorder character of the ferroelectric transition in TAAP [3].…”

“…members of the triglycine sulfate (TGS) family. Relaxational behavior of TAAP was previously studied at a frequency range 10 kHz-0.4 MHz and in a microwave band 1 ΜΗz-77 GHz [2,3].…”

Slow polarization relaxation in non-uniform telluric acid ammonium phosphate crystals

“…TAAP, having a chemical formula Te(OH) 6 •2NH 4 H 2 PO 4 •(NH 4 ) 2 HPO 4 , undergoes a phase transition at ∼321 K, changing its symmetry from the centrosymmetric class 2/m to the polar class m [22]. It is an order-disorder transition involving proton motion with hydrogen bonds [23,24]. The crystals were grown from an aqueous solution at room temperature.…”