Oxygen superstructures throughout the phase diagram of $(\mathbf{Y},\mathbf{C}\mathbf{a})\mathbf{B}{\mathbf{a}}_{\mathbf{2}}\mathbf{C}{\mathbf{u}}_{\mathbf{3}}{\mathbf{O}}_{\mathbf{6}+\mathbf{x}}$

Short-range lattice superstructures have been studied with high-energy x-ray diffuse scattering in underdoped, optimally doped, and overdoped $\rm (Y,Ca)Ba_2 Cu_3 O_{6+x}$. 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 $\mathrm{C}\mathrm{u}{\mathrm{O}}_2$ 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 $\rm (Y,Ca)Ba_2 Cu_3 O_{6+x}$.