High pressure behavior of Ga-doped LaMnO_3: a combined X-ray diffraction and optical spectroscopy study

TL;DR

This study investigates how high pressure influences the Jahn-Teller distortion and structural phases of Ga-doped LaMnO_3 using X-ray diffraction and Raman spectroscopy, revealing pressure-induced symmetry changes and partial suppression of distortions.

Contribution

It provides new insights into the pressure-induced structural transitions and the role of Jahn-Teller distortion in Ga-doped LaMnO_3, including a preliminary phase diagram.

Findings

Pressure induces phase transitions to higher symmetry structures.

Jahn-Teller distortion is reduced but not fully suppressed at high pressure.

Coexistence of distorted and regular octahedra domains observed under pressure.

Abstract

The pressure effects on the JT distortion of three representative compounds belonging to the LaMn_1-xGa_xO_3 (x= 0.2, 0.3, 0.4) family was widely investigated by means of X-ray diffraction and Raman spectroscopy. A compound with a fully JT distorted structure (x=0.2), one with regular octahedra (x=0.6) and one in an intermediate configuration (x=0.3) were selected. A pressure induced transitions from the orthorhombic Pbnm phase towards structures with higher symmetry were observed in all the samples. Both Raman and X-ray data confirm that the most important structural effect of pressure is that of reducing the octahedral distortion. The appearance of a feature in the lattice parameter behavior connected to a structural instability was also detected, pointing out the key role of the JT distortion in stabilizing the manganite structures. On the other hand, the complete suppression of the JT distortion in the high-pressure phases cannot be claimed. The Raman spectra collected from more distorted compounds (x=0.2, 0.3) reveal clearly the coexistence of domains of distorted and more regular octahedra in a certain pressure range. The first sketch of the Pressure vs. Ga-content phase diagram was drawn.