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 $\mathrm{Al}{\mathrm{V}}_{2-x}{\mathrm{Cr}}_x{\mathrm{O}}_4$ with $x=0.125$ was estimated to be about $10–20\mathrm{nm}$. Furthermore, high-resolution lattice images revealed fine mixture of the CO and charge disordered microdomains in $\mathrm{Al}{\mathrm{V}}_{2-x}{\mathrm{Cr}}_x{\mathrm{O}}_4$ 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 $\mathrm{Al}{\mathrm{V}}_{2-x}{\mathrm{Cr}}_x{\mathrm{O}}_4$. 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.

• Received 10 October 2004

DOI:https://doi.org/10.1103/PhysRevB.71.052411