Charge-density waves and superconductivity in theBa1−xKxBiO3−ysystem

Electron diffraction confirms the existence of a cubic phase and a phase having a $\sqrt{2}a\times \sqrt{2}a\times 2a$ supercell in the ${\mathrm{Ba}}_{1-x}{\mathrm{K}}_x\mathrm{Bi}{\mathrm{O}}_3$ system. It is also found that the supercell phase displays an additional incommensurate structural modulation along the [110] cubic direction. Since the modulation is observed in the semiconducting supercell phase and not in the superconducting cubic phase, such an observation leads to speculation that superconductivity in the ${\mathrm{Ba}}_{1-x}{\mathrm{K}}_x\mathrm{Bi}{\mathrm{O}}_3$ system is associated with the disappearance of a charge-density wave.