Effects of iso- and polyvalent substitutions on the short/long-range crystalline order in CuCrO ₂ compounds

Compounds of pristine CuCrO ₂ , doped CuCr _0.96 M _0.03 V _0.01 O ₂ (M = Ti, Mn, Ga and Nb), CuCr _0.96 V _0.04 O ₂ , CuCr _0.97 Mg _0.03 O ₂ , CuCr _0.97 Ni _0.03 O ₂ and CuCr _1-x Fe _x O ₂ (x = 0.03, 0.06, and 0.09) were prepared by conventional solid-state route. Rietveld Refinement method using the Fullprof software confirms the single rhombohedral structure with space group R-3m for all the studied samples. It was found that doped ion having a larger ionic radius shows an increase in the unit cell volume for CuCrO ₂ , while the unit cell volume decreases or remains nearly unchanged for dopant having a slightly smaller ionic radius. Negligible strain is observed in the pristine, Mn, Ga and Nb doped samples, whereas other dopants show strained growth. It was found that samples with Ti and Fe doping exhibit the maximum strain. Although, no significant changes in the frequencies of Raman active modes A _1g and E _g were detected, strong local distortions were observed in the Mn, Ti and Fe doped samples. In addition, the CuCrO ₂ compounds doped with V, Ga, Nb, Ti and Mn ions exhibit splitting of IR active E _u and A _2u modes.