Observation of cation-specific critical behavior at the improper ferroelectric phase transition in Gd2(MoO4)3

TL;DR

This study uses temperature-dependent X-ray diffraction to investigate the structural phase transition in gadolinium molybdate, revealing cation-specific critical behaviors that underpin its improper ferroelectricity.

Contribution

It provides new atomic-scale insights into the structural changes and cation displacements during the phase transition in gadolinium molybdate, a classical improper ferroelectric.

Findings

Different cations exhibit distinct critical behaviors during the phase transition.

The transition involves a shift from tetragonal to orthorhombic symmetry.

Ferroelastic strain correlates with lattice parameter evolution.

Abstract

Gadolinium molybdate is a classical example of an improper ferroelectric and ferroelastic material. It is established that the spontaneous polarization arises as a secondary effect, induced by a structural instability in the paraelectric phase, which leads to a unit cell doubling and the formation of a polar axis. However, previous X-ray diffraction studies on gadolinium molybdate have been restricted by the limited ability to include the entire 2{\theta} range in the analysis, and thus, at atomic scale, much remains to be explored. By applying temperature dependent X-ray diffraction, we observe the transition from the paraelectric tetragonal phase to the orthorhombic ferroelectric phase. The ferroelastic strain is calculated based on the thermal evolution of the lattice parameters and Rietveld refinement of the temperature dependent data reveals that the displacement of different cations follows different critical behavior, providing new insight into the structural changes that drive the improper ferroelectricity in gadolinium molybdate.