Doping effect on the charge ordering in AlV ₂O ₄

Effect of the Cr doping on the stable charge ordering (CO) in the spinal compound AlV ₂O 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 AlV ₂O ₄ becomes short ranged. The size of the CO microdomains in AlV _2-xCr _xO ₄ with x=0.125 was estimated to be about 10-20 nm. Furthermore, high-resolution lattice images revealed fine mixture of the CO and charge disordered microdomains in AlV _2-xCr _xO 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 AlV _2-xCr _xO ₄. Our results suggested that doped Cr ³⁺ ions should serve as a quenched "charge" impurity in the CO structure of AlV ₂O ₄, which is characterized as the charge frustration system.