Structure and electrical properties in the K1/2Bi1/2TiO3-K1/2Bi1/2ZrO3 solid solution (KBT-KBZ).

The present work is devoted to the study of the Zr⁴⁺/Ti⁴ substitution in the K_1/2Bi_1/2Ti_{(1- x)}Zr _xO₃ solid solution ( x = 0.0 to x = 1.0), based upon the K_1/2Bi_1/2TiO₃ (KBT) ferroelectric compound. The tetragonal distortion of KBT is suppressed by this substitution and leads to the cubic compound K_1/2Bi_1/2ZrO₃ (KBZ). These results agree with the values of the ionic radii of the Zr⁴⁺ and Ti⁴ ions ( $r_{{\rm Ti}^{4 + } } $ = 0.605 Å and $r_{{\rm Zr}^{4 + } } $ = 0.72 Å). Close to KBT ( x ≤ 0.05), the symmetry remains tetragonal. For higher values of x, the ' a' lattice parameter (cubic indexing) follows Vegard's law, thus confirming the formation of a solid solution. The transformation from tetragonal to cubic proceeds via an intermediate pseudocubic symmetry (0.1 ≤ x < 0.5), for which the X-ray diffraction peaks present small broadening and asymmetry. For x ≥ 0.5 and up to the KBZ compound ( a ≈ 4.158 Å), the samples are cubic but some extra peaks are also observed, indicating the occurrence of a secondary phase. The microstructure shows fine-grained ceramic samples for the first range, while for the KBZ-rich range the grains are micrometer-sized and associated to very small grains of the secondary phase. Piezoelectricity is observed for the tetragonal and pseudocubic range, the substitution quickly reducing the piezoelectric properties. The measurement of the dielectric properties revealed close to KBT a dielectric anomaly probably associated to the tetragonal-cubic phase transition. For the pseudocubic and cubic range, a broad dielectric anomaly is observed around 300 °C, corresponding to a relaxor behavior. [ABSTRACT FROM AUTHOR]