Jahn-Teller effect in BaTiO(3):Cr(5+): an electron paramagnetic resonance study.

Area of Science:

• Solid State Physics
• Materials Science
• Spectroscopy

Background:

• Barium titanate (BaTiO3) is a crucial ferroelectric material with applications in electronics.
• Understanding defect centers within BaTiO3 is essential for optimizing its properties.
• Chromium (Cr) doping is explored to modify BaTiO3's characteristics.

Purpose of the Study:

• To investigate the electron paramagnetic resonance (EPR) spectra of Cr(I)(5+) defects in BaTiO3 single crystals and powders.
• To determine the g tensor of Cr(I)(5+) defects across different ferroelectric phases.
• To analyze the influence of the Jahn-Teller effect and spontaneous polarization on the defect structure.

Main Methods:

• Electron Paramagnetic Resonance (EPR) spectroscopy at Q-band (34 GHz).
• Variable temperature measurements (50-220 K) on single-crystal and powdered BaTiO3 samples doped with Cr(I)(5+).
• Analysis of g tensor components and their relation to crystallographic axes and defect symmetry.

Main Results:

• The full g tensor for Cr(I)(5+) was determined in the rhombohedral phase, while only principal values were obtained in the orthorhombic phase.
• The Jahn-Teller effect leads to a tetragonally compressed octahedron around the Cr(I)(5+) ion.
• Spontaneous polarization and quadratic field effects break the D(4h) symmetry, introducing rhombic g tensor components dependent on polarization magnitude.

Conclusions:

• The study elucidates the local structure and electronic properties of Cr(I)(5+) defects in BaTiO3.
• Internal stress in ceramic grains affects the Jahn-Teller energy, explaining differences between single-crystal and powder spectra.
• EPR is a powerful tool for probing defect behavior and phase transitions in ferroelectric materials.