Abstract
Neutron powder diffraction experiments on layered manganites ${\mathrm{La}}_{2\ensuremath{-}2x}{\mathrm{Sr}}_{1+2x}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}\phantom{\rule{0ex}{0ex}}(0.32\ensuremath{\le}x\ensuremath{\le}0.40)$ show that coherent lattice anomalies observed at the Curie temperature (lattice parameters, Mn-O bond lengths) reverse sign at $x\ensuremath{\approx}0.36$, coinciding with the maximum ${T}_{C}\ensuremath{\approx}131\mathrm{K}$. Remarkably, the anomalies are completely suppressed at this crossover composition. Incoherent distortions, as measured by anisotropic Debye-Waller factors, undergo an abrupt decrease below ${T}_{C}$. The magnitude of this anomaly changes very little with $x$ and does not display any sign reversal for $x\ensuremath{\approx}0.36$.
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