Enhanced Superconductivity in Close Proximity to Polar-Nonpolar Structural Phase Transition in Se/Te-Substituted PtBi2

The novel CdI2-type compounds Pt(Bi1−xChx)2 (Ch = Se, Te) were synthesized. Powder X-ray diffraction experiments and Rietveld analysis revealed that the partial substitution of Ch for Bi induces a structural phase transition from the noncentrosymmetric polar structure of trigonal PtBi2 (P31m, \(C_{3v}^{2}\), No. 157) to the centrosymmetric nonpolar CdI2-type structure (\(P\bar{3}m1\), \(D_{3d}^{3}\), No. 164), which consists of stacked Pt(Bi1−xChx)2 layers formed by edge-sharing PtBi6 octahedra. Magnetization, electrical resistivity, and specific heat measurements confirmed the emergence of superconductivity at the transition temperature Tc = 1.9–2.4 and 2.0–2.4 K in Pt(Bi1−xSex)2 and Pt(Bi1−xTex)2, respectively. These temperatures are much higher than Tc = 0.6 K of trigonal PtBi2. The superconducting phases lie in the vicinity of the polar-nonpolar structural phase boundary.