High Pressure High Temperature Synthesis of (Ba_1−xK_x)SbO_3+δ with Air-stable Precursors

The perovskite antimonates (Ba_1−xK_x)SbO_3+δ (BKSO) are the Sb analogs of the high-Tc bismuthate superconductors. Hole-doping via K substitution on the Ba site suppresses the charge-density-wave (CDW) ground state of BaSbO₃ and induces superconductivity, making BKSO a critical system for disentangling the superconducting mechanism in this family. However, the perovskite antimonate phase is metastable at ambient pressure and has traditionally required high pressure high temperature (HPHT) synthesis with air-sensitive oxidants (e.g., BaO2), complicating reproducible access to high-quality crystals. We propose HPHT synthesis with alternative air-stable precursors and controlled oxygen chemical potential to establish robust synthesis windows for crystals and to map the coupled roles of pressure, temperature, composition, and oxygen non-stoichiometry δ in stabilizing the superconducting phase.