Oxygen Superstructures Throughout the Phase Diagram of $(\mathrm{Y},\mathrm{C}\mathrm{a})\mathrm{B}{\mathrm{a}}_2\mathrm{C}{\mathrm{u}}_3{\mathrm{O}}_{6+\mathrm{x}}$

The doping dependence of short-range lattice superstructures in $(\mathrm{Y},\mathrm{C}\mathrm{a})\mathrm{B}{\mathrm{a}}_2\mathrm{C}{\mathrm{u}}_3{\mathrm{O}}_{6+\mathrm{x}}$ has been studied with high-energy x-ray scattering. We observe diffuse features with a well defined periodicity which depend on the oxygen concentration but not on the charge carrier concentration. In addition, we find that diffuse scattering is absent in underdoped $\mathrm{Y}\mathrm{B}{\mathrm{a}}_2\mathrm{C}{\mathrm{u}}_4{\mathrm{O}}_8$, which does not sustain oxygen defects. Our combined data highlight that the diffuse scattering arises from short-range oxygen ordering and associated lattice distortions. Signatures of stripe ordering or fluctuations are not seen and therefore must be much weaker.

Figure 1

Diffuse scattering intensities in ${\mathrm{Y}}_{1-\mathrm{y}}\mathrm{C}{\mathrm{a}}_{\mathrm{y}}\mathrm{B}{\mathrm{a}}_2\mathrm{C}{\mathrm{u}}_3{\mathrm{O}}_{6+\mathrm{x}}$. (a) Scans along $(h02.5)$ for the ortho-III phase of ${\mathrm{Y}\mathrm{B}\mathrm{a}}_2{\mathrm{C}\mathrm{u}}_3{\mathrm{O}}_{6.75}$, together with a simulation (solid line) based on the structure found in Ref. 11. (b) $(h05.6)$ scans for both ${\mathrm{Y}\mathrm{B}\mathrm{a}}_2{\mathrm{C}\mathrm{u}}_3{\mathrm{O}}_{6.92}$ ($•$) and ${\mathrm{Y}}_{0.8}{\mathrm{C}\mathrm{a}}_{0.2}{\mathrm{B}\mathrm{a}}_2\mathrm{C}{\mathrm{u}}_3{\mathrm{O}}_{6.95}$ ($\circ$). (c) $l$ scans of ${\mathrm{Y}\mathrm{B}\mathrm{a}}_2{\mathrm{C}\mathrm{u}}_3{\mathrm{O}}_{6.92}$ at both $T=10\mathrm{K}$ and $T=300\mathrm{K}$ along $(4.250l)$. The insets in (a) and (b) show the ortho-III and ortho-IV patterns, respectively, where large full (open) circles denote occupied (unoccupied) oxygen sites.

Figure 2

Temperature dependences of the integrated intensity of (a) the (4.4 0 2.5)/(4.6 0 2.5) reflections in $\mathrm{Y}\mathrm{B}{\mathrm{a}}_2\mathrm{C}{\mathrm{u}}_3{\mathrm{O}}_{6.65}$, (b) the (4.33 0 2.5)/(4.66 0 2.5) reflections in $\mathrm{Y}\mathrm{B}{\mathrm{a}}_2\mathrm{C}{\mathrm{u}}_3{\mathrm{O}}_{6.75}$, and (c) the (5.25 0 5.6) reflection in $\mathrm{Y}\mathrm{B}{\mathrm{a}}_2\mathrm{C}{\mathrm{u}}_3{\mathrm{O}}_{6.92}$. The insets in (a) and (b) show the respective $Q$-scans at low temperature.

Figure 3

Contour plots of the diffuse intensity in the (a) $(hk5.5)$ plane and (b) $(h0l)$ plane of ${\mathrm{Y}}_{0.8}\mathrm{C}{\mathrm{a}}_{0.2}\mathrm{B}{\mathrm{a}}_2\mathrm{C}{\mathrm{u}}_3{\mathrm{O}}_{6.95}$. The main Bragg reflections are masked.

Figure 4

Contour plot of the diffuse intensity in the $(h0l)$ scattering plane of $\mathrm{Y}\mathrm{B}{\mathrm{a}}_2\mathrm{C}{\mathrm{u}}_4{\mathrm{O}}_8$.