High Resolution Neutron Diffraction Study of $\rm La_{1-x}Sr_{x}CoO_{3}$ [$0.2<x<0.35$] Nanoparticles.

The crystal structure and properties of $\rm La_{1-x}Sr-{x}CoO_3$ ($\rm LaSrCoO$) have been extensively studied in bulk crystals. We have extended the studies to nanoparticles of $\rm LaSrCoO$ in the size range of 10-50 nm, synthesized using a hetero-nuclear complex precursor. Particle sizes were determined from TEM measurements. High-resolution neutron diffraction experiments were carried out on the NPDF diffractometer at the Los Alamos National Laboratory to analyze the local structure above and below $T_c$. Data were collected at $T=12, 100$ and $300$ K. We examined the implication of the particle size on the local and average structures using both routine Rietveld and PDF techniques. The `$r$' range dependent PDF analyses indicate distortions from the average crystal structure. The Jahn-Teller distortions, observed earlier in bulk compounds, are not observed in these nanoparticle systems. Preliminary magnetic measurements show that, although $T_c$ is similar to that of the bulk, the spin-glass-like behavior persists even above the critical composition $x=0.18$, unlike the bulk. $M$ vs $T$ plots indicate inhomogeneity. Based on these initial results, the local structure-property correlations will be discussed for all the compositions studied.