BIHFVOX, formulated as Bi4HfxV2−xO11−(x/2)−δ, was a new member of BIMEVOX

family. The system with various dopant concentrations (x = 0 to 0.40) was

prepared by the solid state reaction. The phase stability as a function of

composition was investigated using FT–IR, X-ray powder diffraction, differential

scanning calorimetry and conductivity measurements. For x = 0.05, the α-

polymorph was noticed at room temperature with clear evidence for two successive

transitions; α↔β↔γ at 436 and 561C, respectively. For relatively higher dopant

concentrations, 0.15 ≤ x ≤ 0.20, the β↔γ transition was clearly evident. The

variation of unit cell parameters as a function of temperature for x = 0.20 exhibited

a subtle change in c parameter around 400C due to the vacancy ordering

phenomenon which was associated with occurrence of such transition. However,

the existence of order–disorder, γ′↔γ transition was clearly confirmed for x greater

than 0.25. It was also noticed that the increased dopant concentration of highly

sized and charged Hf4+ ion has a significant role in collapsing the fully disordered

tetragonal into orthorhombic β′-domain at higher temperatures. AC impedance

spectroscopy showed that the ionic conductivity was principally due to the grain

contribution as clearly evident in the increased short-range diffusibility of oxide

ion vacancy in the grains with increasing temperature. The composition

dependence of conductivity exhibited a maximum at x = 0.25 at lower

temperatures.

Influence of Dopant Concentration on the Phase Transition and Ionic Conductivity

in BIHFVOX System. S.Beg, N.A.S.Al-Areqi, A.Al-Alas, S.Hafeez: Physica B,

2009, 404[14-15], 2072-9