Flux growth and physical properties of Mo3Sb7 single crystals

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 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 (3) over barm. The cubic-tetragonal structure transition at 53 K is verified by the peak splitting of (4 0 0) reflection observed by x-ray single crystal diffraction and the dramatic intensity change of the (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 53 K in the temperature dependence of specific heat, and the entropy change across the transition is estimated to be 1.80 J/mol Mo K. The temperature dependence of magnetic susceptibility was measured up to 750 K, and it follows a Curie-Weiss behavior above room temperature. Analysis of the low-temperature magnetic susceptibility suggests a spin gap of 110 K around 53 K. A typical phonon thermal conductivity was observed in the low temperature tetragonal phase. A glassy phonon thermal conductivity above 53 K suggests a structural instability in a wide temperature range. Superconductivity was observed at 2.35 K in the as-grown crystals, and the dimensionless specific heat jump Delta C(T)/gamma T-n(c) was determined to be 1.49, which is slightly larger than the BCS value of 1.43 for the weak-coupling limit. DOI: 10.1103/PhysRevB.87.104515