Valence Variations by B-Site Doping in A-Site Columnar-Ordered Quadruple Perovskites Sm2MnMn(Mn4- xTi x)O12 with 1 ≤ x ≤ 3.

Sm2MnMn(Mn4- xTi x)O12 with 1 ≤ x ≤ 3 were prepared by a high-pressure, high-temperature method at 6 GPa and about 1570-1670 K. They belong to a family of A-site columnar-ordered quadruple perovskites A2A'A″B4O12, where A' is a site with a square-planar coordination and A″ is a site with a tetrahedral coordination. Their crystal structures were investigated using synchrotron X-ray and neutron powder diffraction. They crystallize in space group P42/ nmc (No. 137) with a = 7.41172 Å and c = 7.97131 Å for x = 1, a = 7.54945 Å and c = 7.76756 Å for x = 2, and a = 7.63949 Å and c = 7.70339 Å for x = 3 at 295 K. The determined charge and cation distributions are [Sm3+1.88Mn2+0.12]A[Mn3+]A'[Mn2+0.88Sm3+0.12]A″[Mn3+3Ti4+]BO12 for x = 1, [Sm3+1.91Mn2+0.09]A[Mn2+]A'[Mn2+0.91Sm3+0.09]A″[Mn3+2Ti4+2]BO12 for x = 2, and [Sm3+1.88Mn2+0.12]A[Mn2+0.88Sm3+0.12]A'[Mn2+]A″[Mn2+Ti4+3]BO12 for x = 3. Mn and Ti are distributed randomly in one B site in all compounds with the average oxidation state changing from +3.25 to +3.5 per one B atom, and such flexibility is realized because Mn at the A' site can change its oxidation state between +2 and +3. Sm and Mn are slightly disordered between the A and A″ sites for x = 1 and 2, and between the A and A' sites for x = 3. The x = 1 sample shows spin-canted antiferromagnetic properties with TN = 27 K, and the x = 2 sample, with TN = 62 K. On the other hand, the x = 3 sample is a ferrimagnet, confirmed by neutron diffraction, with TC = 40 K. The x = 3 sample shows relaxor-like dielectric properties below 220 K.