Ferroelectric films of deuterated glycine phosphite: Structure and dielectric properties

Polycrystalline textured films of deuterated glycine phosphite consisting of single-crystal blocks with lateral dimensions $\sim$(50–100) $\mu$m and a thickness $d\sim$ (1–5) $\mu$m have been grown by evaporation on NdGaO$_3$(100) and $\alpha$-Al$_2$O$_3$ substrates with preliminarily deposited interdigitated electrodes, as well as on Al substrates. The $c^*$ $(Z)$ crystallographic axis in the blocks is normal to the film plane, and the $a(X)$ axis and the polar axis $b (Y)$ are oriented in the film plane. The temperature dependences of the capacitance of the structures measured with the interdigitated electrode system reveal a strong dielectric anomaly at the film transition to the ferroelectric state. The phase transition temperature $T_c$ depends on the degree of deuteration $D$ of the glycine phosphite. The maximum value $T_c$ = 275 K obtained in the structures studied corresponds to a degree of deuteration of the glycine phosphite $D\sim$ 50%. The frequency behavior of the dielectric hysteresis loops in glycine phosphite films differs radically from that of the previously studied films of deuterated betaine phosphite, which evidences that polarization switching in these structures proceeds by different mechanisms. It has been that application of a dc bias to the electrodes changes the shape of the dielectric hysteresis loops and shifts them along the electric field axis. The shift of the loops depends on the sign, magnitude, and time of application of the bias. Possible mechanisms underlying the induced unipolarity are discussed.