High pressure exploration in the Li-Ln-V-O system.

Area of Science:

• Materials Science and Solid-State Chemistry
• Crystallography and Structural Analysis
• High-Pressure and High-Temperature Synthesis

Background:

• Understanding the structural behavior of complex oxides under extreme conditions is crucial for discovering new materials.
• Lithium lanthanide vanadates represent a class of compounds with potential applications, yet their high-pressure phase diagrams are largely unexplored.
• Previous studies on LiLa5O5(VO4)2 indicated structural transitions under pressure.

Purpose of the Study:

• To investigate the structural transformations of LiLa5O5(VO4)2 under high pressure.
• To synthesize and characterize novel compounds using high pressure-high temperature (HPHT) conditions.
• To elucidate the crystal structures and building units of the newly obtained materials.

Main Methods:

• In situ high-pressure Raman spectroscopy was employed to monitor structural changes.
• High pressure-high temperature (HPHT) synthesis was utilized to obtain new crystalline phases.
• Crystal structure determination was performed using the antiphase approach, focusing on oxygen-centered [OLn4] building units.

Main Results:

• Two distinct structural changes were observed in LiLa5O5(VO4)2 under pressure.
• Three new compounds were successfully synthesized: β-LiLa5O5(VO4)2 (1), β-LiLa2O2(VO4) (2), and LiNd5O5(VO4)2 (3).
• Compound (1) and (3) exhibit 3D structures, while compound (2) features a 2D layered structure with [La2O2]2+ units and surrounding tetrahedra.

Conclusions:

• High pressure plays a critical role in the synthesis and stabilization of novel structural motifs in vanadate materials.
• The antiphase approach effectively describes the crystal structures, emphasizing the presence of [OLn4] building units.
• The discovered compounds, particularly those with 2D and 3D architectures, warrant further investigation for their physical properties.