The Metal-Insulator Transition in Y1-xCaxTiO3 Caused by Phase Separation

TL;DR

This study investigates the crystal structures of Y1-xCaxTiO3 across various compositions and temperatures, revealing that phase separation between orthorhombic and monoclinic phases drives the metal-insulator transition, with the metallic phase linked to the orthorhombic structure.

Contribution

It provides direct structural evidence that phase separation causes the metal-insulator transition in Y1-xCaxTiO3, highlighting the role of the orthorhombic phase in metallic behavior.

Findings

Phase separation occurs near the M-I transition temperature.

Orthorhombic phase is associated with metallic behavior.

Monoclinic phase appears at higher temperatures.

Abstract

In order to explore the origin of the Metal-Insulator (M-I) transition, the precise crystal structures of the hole-doped Mott insulator system, Y1-XCaXTiO3 (x=0.37, 0.39 and 0.41), are studied for the temperature range between 20K and 300K by the synchrotron radiation (SR) X-ray powder diffraction. For both Y0.63Ca0.37TiO3 and Y0.61Ca0.39TiO3 compositions, the orthorhombic (Pbnm) - monoclinic (P21/n) structural phase transition occurs at around 230K, which is much higher than their own M-I transition temperatures, i.e. 60K and 130K, respectively. For these compositions, the significant phase separation (low-temperature orthorhombic + monoclinic) is also found in the vicinity of the M-I transition temperature. On the other hand, Y0.59Ca0.41TiO3, which dose not exhibit M-I transition and preserve a metallic behavior down to 1.5K, is in two phases state from 20K to 300K. It is concluded that the existence of the phase separation causes the M-I transition in Y1-xCaxTiO3, and the low-temperature orthorhombic phase contributes to the metallic property of this system.