Flux growth and physical properties of Mo3Sb7 single crystals

TL;DR

This study reports the growth of Mo3Sb7 single crystals and provides a comprehensive analysis of their structural, magnetic, thermal, and superconducting properties, revealing a structural phase transition and superconductivity at low temperatures.

Contribution

First detailed neutron diffraction analysis of Mo3Sb7's structure and its phase transition, along with characterization of magnetic and superconducting properties.

Findings

Structural transition at 53K confirmed by diffraction techniques.

Superconductivity observed at 2.35K with a specific heat jump near BCS value.

Presence of a spin gap of 110K and glassy phonon thermal conductivity above 53K.

Abstract

Millimeter sized single crystals of Mo3Sb7 are grown using the self-flux technique and a thorough characterization of their structural, magnetic, thermal and transport properties is reported. The structure parameters for the high-temperature cubic phase and the low-temperature tetragonal phase were, for the first time, determined with neutron single crystal diffraction. Both X-ray powder diffraction and neutron single crystal diffraction at room temperature confirmed that Mo3Sb7 crystallizes in Ir3Ge7-type cubic structure with space group Im-3m. The cubic-tetragonal structure transition at 53K is verified by the peak splitting of (4 0 0) reflection observed by X-ray single crystal diffraction and the dramatic intensity change of (12 0 0) peak observed by neutron single crystal diffraction. The structural transition is accompanied by a sharp drop in magnetic susceptibility, electrical resistivity, and thermopower while cooling. A weak lambda anomaly was also observed around 53K in the temperature dependence of specific heat and the entropy change across the transition is estimated to be 1.80J/molMoK. The temperature dependence of magnetic susceptibility was measured up to 750K and it follows a Curie-Weiss behavior above room temperature. Analysis of the low-temperature magnetic susceptibility suggests a spin gap of 110K around 53K. A typical phonon thermal conductivity was observed in the low temperature tetragonal phase. A glassy phonon thermal conductivity above 53K suggests a structural instability in a wide temperature range. Superconductivity was observed at 2.35K in the as-grown crystals and the dimensionless specific heat jump was determined to be 1.49, which is slightly larger than the BCS value of 1.43 for the weak-coupling limit.