Doping effect on the charge ordering inAlV2O4

Abstract

Effect of the Cr doping on the stable charge ordering (CO) in the spinal compound $\mathrm{Al}{\mathrm{V}}_{2}{\mathrm{O}}_{4}$ was investigated by transmission electron microscopy. It is found that the stable CO is destabilized drastically by substituting Cr ions for V ones and the long-ranged CO in $\mathrm{Al}{\mathrm{V}}_{2}{\mathrm{O}}_{4}$ becomes short ranged. The size of the CO microdomains in $\mathrm{Al}{\mathrm{V}}_{2\ensuremath{-}x}{\mathrm{Cr}}_{x}{\mathrm{O}}_{4}$ with $x=0.125$ was estimated to be about $10--20\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. Furthermore, high-resolution lattice images revealed fine mixture of the CO and charge disordered microdomains in $\mathrm{Al}{\mathrm{V}}_{2\ensuremath{-}x}{\mathrm{Cr}}_{x}{\mathrm{O}}_{4}$ at room temperature. In addition, we found the presence of the characteristic diffuse scattering due to local lattice distortion induced by the Cr substitution in $\mathrm{Al}{\mathrm{V}}_{2\ensuremath{-}x}{\mathrm{Cr}}_{x}{\mathrm{O}}_{4}$. Our results suggested that doped ${\mathrm{Cr}}^{3+}$ ions should serve as a quenched ``charge'' impurity in the CO structure of $\mathrm{Al}{\mathrm{V}}_{2}{\mathrm{O}}_{4}$, which is characterized as the charge frustration system.