We report an observation of a pressure-induced transition from a superconducting (SC) to an insulating (I) phase in single-crystal ${\mathrm{Ba}}_{1-x}{\mathrm{K}}_x{\mathrm{BiO}}_3$ ($x=0.4,0.43,0.52$, and 0.58) superconductors. X-ray diffraction measurements conducted at 20 K reveal a direct relationship between this SC-I transition and a pressure-induced distortion of crystal structure. With increasing pressure, the lattice parameters $a$ and $c$ of the ambient-pressure superconducting tetragonal (T) phase are compressed continuously below a critical pressure ($P_{c1}$), wherein the pressure $\left(P\right)$ dependence of the superconducting transition temperature ($T_c$) displays a small variation. However, upon further compression, the lattice of the compressed T phase displays an anisotropic change, and $T_c$ shows a monotonous decrease. When the pressure reaches $P_{c2}$ ($P_{c2}>P_{c1}$), the compressed T phase collapses along the $c$ axis, followed by the disappearance of superconductivity and the appearance of the insulating phase. This SC-I transition is fully reversible, with the critical pressure increasing alongside the K doping concentration. These findings are strikingly similar to the SC-I transition observed in hole-doped high-$T_c$ cuprate superconductors under pressure. Identifying their commonalities could deepen our understanding of the mechanisms that underlie high-$T_c$ superconductivity in these two oxide superconductors with a perovskite structure.

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• Pressure effects
• Superconductivity
• X-ray diffraction