Structural and thermal studies on the Vsub(1-2x)Msub(x)3+Nbsub(x)O2 and Vsub(1-2x)Msub(x)2+Msub(x)6+O2, systems

It has long been known that the crystal structure and the transition temperature of VO2 can be altered by introducing simple and charge coupled substituent ions into crystalline solution. Experiments have been continued in the present study to discover the effect of charge coupled substitutions of the type M3+Nb5+O4(M = Fe or Cr) and M2+M6+O4(M2+ = Ni, Cu or Mn and M6+ = W, Mo or Te). The structural transitions monoclinic-monoclinic-tetragonal or monoclinic-tetragonal have been identified for each composition and their dependence on the amounts of dopants and ionic radii of ions substituted for V4+ determined. The results of the present findings show that the crystalline solutions containing M3+ + Nb5+ show an initial decrease in the Tsub(tr) followed by an increase as M3+NbO4 is added, while in all M6+ + M2+ substitutions Tsub(tr) is always lowered. The substitution of Cr2WO6 and MnWO4 in the binary Vsub(1-2x)Crsub(x)Vsub(x)O2 crystalline-solution series showed first an increase and then a decrease in the Tsub(tr) for these ternary solid-solutions. (author)