Phase transitions and physical properties of K3Nb3B2O12 and K3Nb3-xMxB2O12 (M = Ta, Sb) crystals

Abstract

This work continues our studies into the nature and mechanisms of phase transitions in K3Nb3B2O12 (KNB) crystals, which have a framework structure with spacious continuous channels and combine ferroelectric, ferroelastic, and superionic properties. Single crystals of KNB-based solid solutions in which Nb5+ is partially substituted with Ta5+ (KNBT) or Sb5+ (KNBS) are grown from off-stoichiometric melts. The KNBT solid solutions containing more than 15 at. % Ta are found to decompose at room temperature. The introduction of Ta leads to marked broadening of phase transitions but has little effect on the transition temperatures. KNBS solid solutions exist in a limited composition range. Increasing the Sb content shifts the high-temperature phase transitions to much lower temperatures and raises the electric conductivity of the crystals by 1–1.5 orders of magnitude.