Ferroelectric-Antiferroelectric Phase Transition in Li_0.12Na_0.88Ta_0.4Nb_0.6O₃ Ceramics

Lattice defects and considerable diversity of the degree of ion ordering at substitution of ions of different valences in complex (A′A″)(B′B″)O ₃ oxide structures generate wide variations in material properties. The complex perovskite structures of double oxides are currently known as relaxors and ion superconductors.

Formation of BO ₆ octahedrons and AO ₁₂ polyhedrons is varied by the ratio of components in ferroelectric (Li, Na)(Ta, Nb)O ₃ perovskite structures. The state of ionic superconductivity is attained at the Na:Li = 7:1 ratio. The regions of morphotropic transitions between the rhombic and rhombohedric phases are changed with the change of the Ta and Nb proportion. Raman studies of Li _0.12 Na _0.88 Ta _0.4 Nb _0.6 O ₃ have shown the ferroelectric–antiferroelectric phase transition being of the ordering type and related to increasing anharmonicity of the symmetric vibration.

Keywords:

• Ferroelectrics
• phase transitions
• ceramics
• Raman spectra

AIP PACS:

• 77.80.Bh
• 77.84.−s
• 78.30.−j
• 64.70.Kb