Preparation of CaMn7O12 single phase ceramics


Variety of multiferroic materials is prepared in our department. One of them was CaMn7O12 which exhibits strong magnetoelectric coupling. Small crystals (~ 0.1 mm) were prepared from high temperature solution of CaCl2 and MnO2, but they contained 9% of undesirable admixtures. An alternative method – modified sol-gel synthesis using water solutions of Ca and Mn nitrates and malic acid – produced pure CaMn7O12 powder with less than 1% admixtures. However, this method was not reproducible. Using ethylene glycol instead of malic acid (modified Pechini method) gives reproducible results, no admixtures were detected by powder XRD. The ceramic pellets were prepared by uniaxial pressing and sintering and were used for spectroscopic measurements.

Uniaxial pressing of powders for ceramics preparation – pressing die (a) and hydraulic press (b). The pressed powder is filled into the die and is compressed between two pistons (13 mm in dia) using a hydraulic press. The pistons and die cylinder are made from hard metal. Maximum permissible pressure is 739 MPa.