Ceramic samples, produced by conventional sintering method in ambient air,
6H-SrMnO3​(6H-SMO), 15R-BaMnO3​(15R-BMO),
4H-Ba0.5​Sr0.5​MnO3​(4H-BSMO) were studied. In the XRD measurements
for SMO the new anomalies of the lattice parameters at 600-800 K range and the
increasing of thermal expansion coefficients with a clear maximum in a vicinity
at 670 K were detected. The NeËŠel phase transition for BSMO was
observed at TN​=250 K in magnetic measurements and its trace was detected in
dielectric, FTIR, DSC, and DMA experiments. The enthalpy and entropy changes of
the phase transition for BSMO at TN​ were determined as 17.5 J/mol and 70
mJ/K mol, respectively. The activation energy values and relaxation times
characteristic for relaxation processes were determined from the Arrhenius law.
Results of ab initio simulations showed that the contribution of the exchange
correlation energy to the total energy is about 30%.Comment: 12 pages, 12 figure