X-Ray Determination of Anharmonicity inV3Si

X-ray intensities from over 1000 reflections in single-crystal ${\mathrm{V}}_3$Si at 300, 78, and 13.5 K, previously obtained by one of us (J.-L.S.) have been analyzed for anharmonicity when ${\lambda }^{-1\mathrm{}}sin\theta >0.7\mathrm{}$ ${\mathrm{\AA }}^{-1\mathrm{}}$ where diffraction occurs from core electrons only. At 78 K we find $〈{\mu }^2〉$ and $〈{\mu }^4〉$ moments for V which are ∼ 50% and 500% larger, respectively, than expected for a harmonic lattice, and evidence for localization of the V atoms off the lattice sites by ∼0.2 Å. No evidence of such large anharmonicity is found for Si atoms at all three temperatures.