Ti-doping effect on the MI transition of hollandite vanadate,K2V8O16

Abstract Ti-doping effect on the metal-insulator transition of hollandite vanadate, K2V8O16 has been investigated. The transition is accompanied by the charge ordering and the structural change from tetragonal to monoclinic structures with the increase of volume in the low-temperature monoclinic insulator phase. A slight amount of Ti-substitution for V atoms raises the transition temperature up to 270 K at x = 0.5 in K 2 V 8 - x Ti x O 16 from 170 K at x = 0 . This significant rise of transition temperature can be understood as a negative chemical pressure effect caused by the Ti-substitution. On the other hand, the disorder effect from the Ti-substitution makes the transition broad and finally the transition smears out around x = 1.0 .