Structural Conditionality of the Ionic Conductivity of MTiORO4 (M = K, Rb; R = P, As) Single Crystals

Abstract

The ionic conductivity σ_||c along the crystallographic axis c and the structural imperfection of the lattices of KTiOPO₄, RbTiOPO₄, and RbTiOAsO₄ single crystals with low defect concentration, grown by the high temperature solution growth technique, have been investigated by impedance spectroscopy and X-ray diffraction analysis. Isomorphic substitutions of Rb⁺ ions for conduction K⁺ cations in MTiOPO₄ crystals decreases the σ_||c value, whereas the substitution of As⁵⁺ ions for framework P⁵⁺ cations in RbTiORO₄ crystals increases the σ_||c value. The σ_||c values at 573 K are found to be 1.0 × 10^–5, 5.7 × 10^–6, 2.0 × 10^–6, and 3.3 × 10^–5 S/cm for the KTiOPO₄, RbTiOPO₄ {100}, RbTiOPO₄ {201}, and RbTiOAsO₄ crystals, respectively (the growth zone of the crystalline boule from which the samples were cut is indicated in braces).