Dipole-glass behavior of lightly dopedKTa1−xNbxO3

Abstract

High-resolution x-ray diffraction measurements have been performed between 10 and 300 K on several single crystals of ${\mathrm{KTa}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Nb}}_{\mathit{x}}$ ${\mathrm{O}}_3$ with x≤0.157. Contary to the published phase diagram, no deviation from cubic symmetry is seen for x≤0.060. Instead, a low-temperatue minimum to the cubic unit cell volume is observed at a temperature ${\mathit{T}}_{\min }$ which increases monotonically for 0.012≤x≤0.060. Data for x=0.157, however, are consistent with the previously established sequence of structural transitions from cubic to tetragonal to orthorhombic to rhombohedral symmetries. We associate ${\mathit{T}}_{\min }$ with the onset of a dipolar glass transition. In addition, a radial broadening of the linewidths is observed at ${\mathit{T}}_{\min }$, indicating the presence of strain in the lattice. Powdering small pieces from these single crystals suppresses the unit cell minimum and stabilizes the cubic phase down to 10 K, even for x=0.157.