| Summary: | BaPb<sub>1−x</sub>Bi<sub>x</sub>O<sub>3</sub> (BPBO) bismuthate, showing high T<sub>C</sub> superconductivity for 0.05 < x < 0.35, is an archetypal system for studying the complex inhomogeneity of perovskite lattice favoring the emergence of quantum coherence, called the superstripes phase. Local lattice fluctuations, detected by EXAFS; nanoscale stripes, detected by electron microscopy; and two competing crystalline structures, detected by diffraction, are known to characterize the superconducting phase. At nanoscale [BaBiO<sub>3</sub>] centered nanoscale units (BBO) coexist with BaPbO<sub>3</sub> centered (BPO) units in the BPBO perovskite; therefore, we expect a tensile microstrain in BPO units due the misfit strain between the two different lattices. Here, we report the measurement of the spatial micro-fluctuations of the local tensile microstrain ε in the BaPO units in superconducting Ba(Pb<sub>1−x</sub>Bi<sub>x</sub>)O<sub>3</sub> crystals with x<sub>1</sub> = 0.19 an x<sub>2</sub> = 0.28. We show here the feasibility of applying the scanning dispersive micro-X-ray absorption near edge structure (SdμXANES) technique, using focused synchrotron radiation, to probe the microscale spatial fluctuations of the microstrain in BPO units. This unconventional real-space SdμXANES microscopy at the Pb <i>L</i><sub>3</sub> edge has been collected in the dispersive mode. Our experimental method allows us to measure either the local Bi chemical concentration x and the local lattice microstrain of local BBO and BPO units. The 5 × 5 micron-size spots from the focused X-ray beam allowed us to obtain maps of 1600 points covering an area of 200 × 200 microns. The mapping shows a substantial difference between the spatial fluctuations of the microstrain ε and the chemical inhomogeneity x. Moreover, we show the different relations ε(x) in samples with lower (x<sub>1</sub> = 0.19) and higher (x<sub>2</sub> = 0.28) doping respect to the optimum doping (x = 0.25).
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