Pressure effect and electron diffraction on the anomalous transition in ternary superconductor Bi2Rh3Se2

●The superconducting transition (Tc) of K Bi2Rh3Se2 is at 0.68 K.●The transport property under pressure is inconsistent with results observed in conventional CDW formation.●A structural transition occurs below 250 K, from monoclinic C12/m1 to P12/m1.

The effect of external hydrostatic pressure up to 22.23 kbar on the temperature-dependent transport properties of the ternary compound Bi2Rh3Se2 is investigated. Interestingly, the resistive anomaly at Ts~250 K, previously proposed as a charge-density-wave (CDW) transition, is shifted to higher temperature with increasing pressure, in distinct contrast to an established knowledge for CDW. Using temperature-dependent electron-diffraction characterizations, we have unraveled that this transition is, in effect, of a structural phase-transformation nature, experiencing the symmetry reduction from a high-symmetry C-centered monoclinic lattice to a low-symmetry primitive one below Ts. A more elaborately determined room-temperature C-centered lattice was also proposed.