Enhanced Spontaneous Polarization by V⁴⁺ Substitution in a Lead-Free Perovskite CaMnTi₂O₆

Spontaneous polarization (P_s) of novel order–disorder type lead-free ferroelectric CaMnTi₂O₆ was successfully enhanced by partial V⁴⁺ substitution for Ti⁴⁺. A synchrotron X-ray diffraction study revealed that the polar displacement of octahedrally coordinated (Ti, V) in CaMn­(Ti_1–xV_x)₂O₆ (0 ≤ x ≤ 0.4) increases with V⁴⁺ substitution having Jahn–Teller activity owing to the d¹ electronic configuration. Our magnetic study suggested the presence of antisite disorder between Ca²⁺ and square planar coordinated Mn²⁺ associated with Mn–V intermetallic charge transfer for x ≥ 0.4, resulting in decreases in spontaneous polarization and the ferroelectric–paraelectric transition temperature. This is the first report on the enhanced polarization owing to the Jahn–Teller distortion of V⁴⁺ without stereochemical Pb²⁺ or Bi³⁺.