Influence of temperature and oxygen pressure on the stability of barium or strontium doped neodymium manganites
Processing and Application of Ceramics
In this work neodymium manganites, Nd 1-x A x MnO 3±δ , doped with Ba or Sr (where x = 0.15 and 0.25) were obtained by ceramic technology at 1250°C. In order to obtain materials with stable thermal and electrical properties, their structure and physicochemical properties were studied depending on the dopant type and its concentration. It was established that the manganites doped with strontium (for x = 0.15 and 0.25) and barium (for x = 0.15) have the Jahn-Teller distortion of the structure,
... f the structure, but it was not observed for the sample Nd 0.75 A 0.25 MnO 3±δ . The sequence of phase transformations was studied under conditions of reduced oxygen pressure in gaseous phase using thermal analysis in combination with XRD. The influence of temperature and oxygen pressure on the stability limit of the manganites was investigated. The studied manganites remain stable in the range of partial oxygen pressures P O 2 from 0.21 to 10 −14 atm at 800°C. An increasing in the dopant concentration leads to the increase of manganite electrical conductivity without decreasing the thermal stability limit. ganites  . Variation of dopant concentration in wide range affects the magnetic, structural, charge and orbital ordering    . At some ratios of Mn 3+ /Mn 4+ there are various types of orders and superstructures in these compounds [5, 21] . For a reasonable choice of an optimal composition of the compounds for practical use, information about physicochemical characteristics of the corresponding systems and their phases are needed. Information about the oxygen content in various compositions of Ln 1-x A x MnO 3 perovskites and its most important properties, such as electrical conductivity and thermal stability, and their dependence on external parameters are scarce. The purpose of this work is to establish relationship between the chemical composition and physicochemical properties of oxides at different temperatures and oxygen partial pressures.