Oxygen superstructures throughout the phase diagram of $(\mathbf{Y},\mathbf{Ca})\mathbf{B}{\mathbf{a}}_2\mathbf{C}{\mathbf{u}}_3{\mathbf{O}}_{6+\mathbf{x}}$

Abstract

Short-range lattice superstructures have been studied with high-energy x-ray diffuse scattering in underdoped, optimally doped, and overdoped $(\mathrm{Y},\mathrm{Ca})\mathrm{B}{\mathrm{a}}_2\mathrm{C}{\mathrm{u}}_3{\mathrm{O}}_{6+\mathrm{x}}$. A new four-unit-cell superstructure was observed in compounds with $x\sim 0.95$. Its temperature, doping, and material dependence was used to attribute its origin to short-range oxygen vacancy ordering, rather than electronic instabilities in the $\mathrm{Cu}{\mathrm{O}}_2$ layers. No significant diffuse scattering is observed in YBa${}_2$Cu${}_4$O${}_8$. The oxygen superstructures must be taken into account when interpreting spectral anomalies in $(\mathrm{Y},\mathrm{Ca})\mathrm{B}{\mathrm{a}}_2\mathrm{C}{\mathrm{u}}_3{\mathrm{O}}_{6+\mathrm{x}}$.