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Methods of their synthesis, processes of cation substitution and cation exchange in metal-oxide compounds with a double perovskite structure

Synthesis of Sr2FeMoO6-δ

The synthesis of the Sr2FeMoO6-δ ( (SFMO) is carried out from the basic reagents SrCO3, Fe2O3, MoO3 in the following way:

  1. mixing the initial powder reagents in a stoichiometric ratio
  2. pressing of the powder
  3. preliminary annealing
  4. grinding
  5. pressing of the powder
  6. final annealing
  7. obtaining a predetermined oxygen index of SFMO.


In order to reduce the concentration of antisite defects [Fe]Mo and [Mo]Fe samples SFMO. Synthesis is carried out in evacuated quartz ampoules in the presence Thais (Fe) at T = 1420K and pO2=10-8Pa within 15 hours.

Schematic representation of the cell for the synthesis of SFMO with a predetermined oxygen index.


Microstructure of Sr2FeMoO6-δ samples, synthesized from SrСO3, Fe2O3 and SrMO4

A sample synthesized from simple oxides contains porous microstructure. It also contains conglomerates with lengths up to 40 μm. These conglomerates consist of close-packed grains with a medium diameter 3 μm.


Phase transformations at SFMO synthesis from Fe2O3 (FO), MO3 (MO) and SrСO3 (SCO)

In order to optimize SFMO synthesis conditions, sequence of phase transitions by X-ray analysis of quenched sample during solid state synthesis was investigated. In this case we studied the sample No. 1 which consists of simple oxide mixture in stoichiometric ratio. It was found that initially the SMO phase was formed at ~ 770 K. The X-ray diffraction peaks of SFO and SFMO appeared simultaneously at about 970K. At the further temperature increase SFO diffraction peaks disappeared in the temperature region from 970 to 1170 K, while that of SMO remained up to 1370 K. The temperature of homogenious phase formation SFMO was 1420 K..


Microstructure of samples Sr2FeMoO6-δ synthesized from SrFeO3-х and SrMO4-y

The sample No. 2 synthesized from mixture of SFO and SMO precursors has more dense microstructure than that of the sample No.1. The average grain diameter for the SFMO sample No.2 is 2 μm. Large conglomerates were not observed. The SFMO growth rate was larger for the sample No. 2.


Phase transformations at SFMO synthesis from SrFeO3-d (SFO) and SrMO4 (SMO)

To eliminate the formation of intermediate reaction products and accelerate the processes of nucleation and growth of SFMO, SFO and SMO precursors were used as initial reagents. In this case we studied the sequence of phase transitions in the sample No.2, which consists of SFO and SMO mixture of partially reduced precursors in stoichiometric ratio. It was established that the SFMO phase was formed at 870 K. The temperature of SFMO single-phase formation decreased on 100 K.



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