| Raman spectra of the Mg2CrV3O11 and Zn2CrV3O11 compounds were investigated and analyzed showing many similarities. X-ray diffraction studies of polycrystalline samples of Zn2CrV3O11 and Mg2CrV3O11 were performed. In case of Mg2CrV3O11 we have obtained fairly good structure refinement. The symmetry of Mg2CrV3O11 is triclinic space group P-1 with parameters: a = 0,6276(5) nm, b = 0,6705(2) nm, c = 1,123(2) nm, α = 113,9º, β = 106,4º, γ = 94,9º, Z = 2. It is isostructural with MgxZn2-xGaV3O11. In Mg2CrV3O11, the Cr3+ ion is distributed non-statistically with Mg2+ on two octahedral (M(1)O6 and M(2)O6) and one bipyramidal sites (M(3)O5). Site-independent population refinements in the whole collected 2theta (8°-159°) range, and, correction made for the effect of finite sample size at the lowest angles, gave rise to the following distributions: M(1)=0.7Cr+0.3Mg, M(2)=0.24Cr+0.76Mg and M(3)=0.03Cr+0.97Mg. These distributions are different from those of Fe atoms in isostructural Mg2FeV3O11 compound. Magnetic measurements were carried out for both compounds. The temperature dependence of the magnetic susceptibility of Cr3+-Cr3+ dimers have been found using standard Van Vleck formula. The exchange constant J between Cr3+ ions has been successfully calculated taking also into account exchange interactions between dimers. Exchange constant between Cr3+ ions in dimer, J1/kB, calculated from magnetic susceptibility results, stay in good agreement with J calculated from EPR results. |
full paper (pdf, 224 Kb)