Structural and solid-state examination of Ca₄Mn₃O₁₀ and Sr₄Mn₃O₁₀

A comparative study of the manganates Ca₄Mn₃O₁₀ and Sr₄Mn₃O₁₀ shows them to belong to distinct structural classes, of Ruddlesden-Popper and Cs₄Ni₃F₁₀ type respectively. Our determinations show both compounds to be orthorhombic, with Ca₄Mn₃O₁₀ in space group Ccc2, with a = 5.240, b = 26.823, c = 5.276 A. and Sr₄Mn₃O₁₀ in space group P222₁. with the cell dimensions of a = 5.481(1). b = 6.237(1), c = 12.528(2) A. In addition, Ca₄Mn₃O₁₀ is found to undergo a transition at 122 K, below which temperature there is evidence for antiferromagnetic ordering and for a sharp conductor-to-insulator transition. This appears to be a new form of giant magnetoresistance (GMR). differing from previous reports in that it occurs in an undoped, layered bulk perovskite.