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Evolution of the average and local crystal structure of Ca-doped LaMnO$_{3}$has been studied across the metal to insulator (MI) and the orthorhombic torhombohedral (OR) structural phase transitions over a broad temperature rangefor two Ca concentrations ($x = 0.18; 0.22$). Combined Rietveld and high realspace resolution atomic pair distribution function (PDF) analysis of neutrontotal scattering data was carried out with aims of exploring the possibility ofnanoscale phase separation (PS) in relation to MI transition, and charting theevolution of local Jahn-Teller (JT) distortion of MnO$_{6}$ octahedra acrossthe OR transition at T$_{S}$ $\sim$ 720 K. The study utilized explicittwo-phase PDF structural modeling, revealing that away from TMI there is noevidence for nanoscale phase coexistence. The local JT-distortions disappearabruptly upon crossing into the metallic regime both with doping andtemperature, with only small temperature-independent signature of quencheddisorder being observable at low temperature as compared to CaMnO$_{3}$. Theresults hence do not support the percolative scenario for the MI transition inLa$_{1-x}$Ca$_{x}$MnO$_{3}$ based on PS, and question its ubiquity in themanganites. In contrast to LaMnO3 that exhibits long range orbital correlationsand sizeable octahedral distortions at low temperature, the doped samples withcompositions straddling the MI boundary exhibit correlations (in the insulatingregime) limited to only $\sim$ 1 nm with observably smaller distortions. In $x= 0.22$ sample local JT-distortions are found to persist across the ORtransition and deep into the R-phase (up to $\sim$ 1050 K) where they arecrystallographically prohibited. Their magnitude and subnanometer spatialextent remain unchanged.

physical review. b./physical review. b

Non percolative nature of the metal-insulator transition and persistence  of local Jahn-Teller distortions in the rhombohedral regime of  La$_{1-x}$Ca$_{x}$MnO$_{3}$