Raman Study of the Structural Distortion in the Ni1-xCoxTiO3 Solid Solution

Area of Science:

• Materials Science
• Solid-State Chemistry
• Condensed Matter Physics

Background:

• Ilmenite oxides (Ni1-xCoxTiO3) are complex materials with potential applications in electronics and magnetism.
• Understanding their structural and magnetic properties is crucial for designing novel functional materials.

Purpose of the Study:

• To investigate the temperature-dependent structural and magnetic properties of Ni1-xCoxTiO3 ilmenites.
• To elucidate the relationship between structural distortions, magnetic ordering, and charge transfer mechanisms.

Main Methods:

• Raman spectroscopy was employed to analyze structural changes across a wide temperature range (4–1200 K).
• The study focused on Ni1-xCoxTiO3 samples with varying cobalt concentrations (0 ≤ x ≤ 1).

Main Results:

• A significant symmetry lowering from the R3̅ prototype was observed, with maximum distortion in samples where x = 0.40 and 0.50.
• Structural distortion persisted across the entire temperature range, with notable exceptions for specific compositions.
• Ferromagnetic order was detected in the x = 0.40 sample between 25 and 69 K, coinciding with structural distortion.
• A reversible ilmenite-corundum phase transformation occurred at 973 K in the x = 0.50 sample.

Conclusions:

• Cation-cation and oxygen-mediated interactions are proposed as drivers for structural distortion and magnetic order.
• Orbital overlap of Co/Ni and Ti 3d orbitals through oxygen octahedral faces plays a role in charge transfer.
• The study provides a comprehensive understanding of the interplay between structure, magnetism, and phase transitions in Ni-Co titanate ilmenites.