Microhardness of Crystals of Lithium Niobate Tantalate LiNb_1–xTa_xO₃ Solid Solutions

Growth of solid solutions of intermediate compositions of LiNb_1–xTa_xO₃ (lithium niobate tantalate, LNT) crystals allows us to adjust the physical parameters of the material and obtain crystals with the required properties, which is why obtaining such crystals and studying their properties taking into account anisotropy is an urgent task. Crystals of solid solutions of LNT composed of LiNb_0.88Ta_0.12O₃ and LiNb_0.93Ta_0.07O₃ are grown in this study. Polished samples oriented in the standard installation were prepared from these crystals. The samples are subjected to monodomenization. The polarity of the piezoactive faces is determined. By optical microscopy in transmitted light, patterns in the form of a sponge-like structure are observed on all samples of Z-cuts, patterns in the form of vertical regions parallel to the optical axis (Z axis) are observed on samples of X- and Y-cuts. Taking into account anisotropy and polarity, measurements of the mechanical characteristics of the samples at a load of 25 Gs are carried out: the microhardness of the samples according to the Vickers hardness (H_V) calculated on the Mohs scale H_M and the brittleness score Z_x. According to the obtained data, the parameters of the viscosity S according to the Palmquist method and the degree of ionic bonds are calculated. The effect of the Nb : Ta ratio on the microhardness of Z-cuts is ambiguous, this may be due to the significant heterogeneity of such samples. In the case of X-cut samples, the results of microhardness measurements are close to each other and within the error limits of the method. In the case of Y-cuts, there is a significant difference in the values of microhardness and brittleness of Y+ and Y– sections, while the microhardness of the sample with a higher Nb content is higher.