Lateral deformations of a crystal of potassium acid phthalate in an external electric field

Abstract

The anisotropy of deformations in potassium acid phthalate crystals arising under the action of an external electric field up to 1 kV mm−1 applied along the [001] polar axis was studied using X-ray diffraction methods at room temperature. Electrical conductivity was measured and rocking curves for reflections 400, 070 and 004 were obtained by time-resolved X-ray diffractometry in Laue and Bragg geometries. Two saturation processes were observed from the time dependences of the electrical conductivity. A shift in the diffraction peaks and a change in their intensity were found, which indicated a deformation of the crystal structure. Rapid piezoelectric deformation and reversible relaxation-like deformation, kinetically similar to the electrical conductivity of a crystal, were revealed. The deformation depended on the polarity and strength of the applied field. The deformation was more noticeable in the [100] direction and was practically absent in the [001] direction of the applied field. X-ray diffraction analysis revealed a disordered arrangement of potassium atoms, i.e. additional positions and vacancies. The heights of potential barriers between the positions of K+ ions and the paths of their possible migration in the crystal structure of potassium acid phthalate were determined. The data obtained by time-resolved X-ray diffractometry and X-ray structure analysis, along with additional electrophysical measurements, allow the conclusion that the migration of charge carriers (potassium cations) leads to lateral deformation of the crystal structure of potassium phthalate in an external electric field.

Study of the piezoelectric properties of rubidium acid phthalate crystals by time-resolved three-crystal X--ray diffractometry

“…The fact that he rubidium biphthalate is free from the charge carrier migration effects found in potassium biphthalate is presumably connected with the considerably higher activation energy of rubidium ions, which is confirmed by an order of magnitude difference in resistances of the abovementioned crystals [24].…”

“…In [24] it was found in crystals of potassium biphthalate that application of external electric field results in emergence of two strain types: fast straindue to piezoelectric effect, and relaxation straindue to migration of potassium ions under the field. It was shown, that the second mechanism is characterized by a threshold value of field strength exceeding 500 V/mm, which is defined by the energy of potassium ions activation.…”

Исследование Пьезоэлектрических Свойств Кристаллов Бифталата Рубидия Методом Времяразрешающей Трехкристальной Рентгеновской Дифрактометрии

“…В работе [24] в кристаллах бифталата калия было обнаружено, что приложение внешнего электрического поля приводит к появлению двух видов деформаций: быстрой -за счет пьезоэлектрического эффекта, и релаксационной -за счет миграции ионов калия под полем. Было показано, что для второго механизма характерно пороговое значение напряженности поля более 500 V/mm, определяемое энергией активации ионов калия.…”

“…Отсутствие в бифталате рубидия эффектов миграции носителей заряда, обнаруженных в бифталате калия, предположительно связано с существенно большей энергией активации ионов рубидия, что подтверждается разницей сопротивления указанных кристаллов на порядок величины [24].…”