Various valence states of square-coordinated mn in a-site-ordered perovskites.

A-site-ordered perovskites LaMn(3)Cr(4)O(12) and LaMn(3)Ti(4)O(12) were synthesized under high-pressure and high-temperature conditions. The charge formula of LaMn(3)Cr(4)O(12) was found to be LaMn(3+)(3)Cr(3+)(4)O(12) with Mn(3+) at the square-coordinated A site. The valence of the A-site Mn ions in LaMn(3)Ti(4)O(12) appeared to be less than +2, and the charge combination in this compound seemed to be LaMn(1.67+)(3)Ti(4+)(4)O(12). Although the square-coordinated A site in A-site-ordered perovskites has been widely known to be occupied by Jahn-Teller active Mn(3+), the present results show that the valence of Mn at the A site can vary from +3 to possible +1.67.