Abstract
A series of trivalent transition metal germanates with a general formula of A3M2Ge4O14 (A = Sr, Ba, M = Mn and Fe) was synthesized using a high-temperature (580 °C) hydrothermal technique. Compound I, Ba3Mn2Ge4O14, is a new structure type that is characterized by one-dimensional Mn–O–Mn chains made from edge-sharing highly distorted Mn3+O6 units, and exhibits antiferromagnetic behavior below 15 K with field induced metamagnetic transitions. The A3Fe2Ge4O14 (A = Sr and Ba, II and III, respectively) series belongs to the well-known langasite structure type, crystallizing in space group P321. In A3Fe2Ge4O14, there is one octahedral Fe3+ site and one mixed-occupancy Fe3+/Ge4+ site that form the one-dimensional substructure. The magnetic susceptibility data of Ba3Fe2Ge4O14 reveals a much simpler magnetic structure with an antiferromagnetic transition near 5.5 K. The Jahn-Teller distortion of Mn3+ appears to be influential in the phase formation, leading to significantly different structures for these Mn3+ and Fe3+ compounds with similar chemical formulas.
