Gd2CuZnMn4O12: A-site columnar-ordered perovskite with anisotropic thermal expansion and a gradual charge-order transition

A new A-site columnar-ordered quadruple perovskite, Gd2CuZnMn4O12, was synthesized by a high-pressure, high-temperature method at 6 GPa and 1500 K. Its structural properties between 100 K and 800 K were investigated by synchrotron powder X-ray diffraction. It has space group Pmmn (No. 59) between 100 K and about 450 K with a layered charge order (CO) of Mn3+ and Mn4+ cations at the perovskite B sites and space group P4(2)/nmc (No. 137) above 475 K with one perovskite B site (having an average manganese oxidation state of +3.5). Anisotropic thermal expansion was observed as the c lattice parameter decreases with increasing temperature above 325 K. Temperature dependence of the unit-cell volume and the lattice parameters and differential scanning calorimetry measurements gave evidence that the CO transition (with T-CO approximate to 475 K) is of the second order. Gd2CuZnMn4O12 shows a ferrimagnetic transition below T-C = 105 K with an additional decrease of magnetic susceptibilities below about 45 K, probably caused by a gradual increase of the ordered moments on the Gd sublattices coupled antiferromagnetically with the existent ferrimagnetic structure.