The High-Pressure Oxide Tb₃ O₅ and its Non-Centrosymmetric Low-Temperature Polymorph-A Comprehensive Study

Area of Science:

• Solid State Chemistry
• Materials Science
• Rare Earth Oxides

Background:

• Mixed-valent rare earth oxides are crucial in advanced materials applications.
• Understanding their synthesis and properties under extreme conditions is vital for discovering new functionalities.
• Previous research has limited characterization of such compounds under high-pressure/high-temperature (HPHT) synthesis.

Purpose of the Study:

• To synthesize and thoroughly characterize a novel mixed-valent binary rare earth oxide.
• To investigate the structural and magnetic properties of the synthesized compound and its low-temperature polymorph.
• To explore phase transitions under varying temperature conditions.

Main Methods:

• High-pressure/high-temperature (HPHT) synthesis using an equimolar mixture of Tb4O7 and Tb2O3 at 8 GPa and 1323 K.
• Single-crystal X-ray structure determination to elucidate crystal structure and space group (Pnma).
• Temperature-dependent magnetic susceptibility, heat capacity measurements, and synchrotron X-ray powder diffraction to analyze magnetic ordering and phase transitions.

Main Results:

• Successful synthesis of crystalline high-temperature/high-pressure terbium oxide (HT-HP-Tb3O5) in the orthorhombic Pnma space group.
• HT-HP-Tb3O5 exhibits Curie-Weiss paramagnetic behavior with an effective magnetic moment of 9.21(2) μB, showing antiferromagnetic ordering at TN = 3.6(1) K.
• A displacive structural phase transition from Pnma to Pn21a occurs at low temperatures, forming the LT-HP-Tb3O5 polymorph.

Conclusions:

• The first thoroughly characterized mixed-valent binary rare earth oxide, HT-HP-Tb3O5, synthesized under HPHT conditions, has been reported.
• The study reveals complex magnetic and structural properties, including antiferromagnetic ordering and a low-temperature displacive phase transition.
• The findings provide new insights into the behavior of rare earth oxides under extreme conditions and their potential for novel applications.