Dielectric and structural properties of ferroelectric betaine arsenate films

Ferroelectric films of betaine arsenate and partially deuterated betaine arsenate have been grown by evaporation on LiNbO$_3$, $\alpha$-Al$_2$O$_3$, and NdGaO$_3$ substrates with a preliminarily deposited structure of interdigitated electrodes, as well as on the Al/glass substrate. This paper presents the results of the examination of the block structure of the films in a polarizing microscope, the X-ray diffraction analysis of their crystal structure, and the investigation of the dielectric properties in a measuring field oriented both parallel and perpendicular to the plane of the film. The transition of the films to the ferroelectric state at $T = T_c$ is accompanied by anomalies of the capacitance of the structure, an increase in the dielectric loss, and the appearance of dielectric hysteresis loops. The growth of the films from a solution of betaine arsenate in a heavy water leads to an increase in the ferroelectric transition temperature from $T_c$ = 119 K in the films without deuterium to $T_c$ = 149 K, which corresponds to the degree of deuteration of approximately 60–70%. The dielectric and structural properties of the films are compared with those of the betaine arsenate single crystals and the previously studied films of betaine phosphite and glycine phosphite.