In English

Abstract

At present silicates of one of the rare earth elements, such as neodymium, are used in various fields of technology as materials or components for lasers, solid state fuel cells, ceramics and others because of their optical, electrical, chemical and mechanical properties. Among them, Nd 9.33 Si 6 O 26 with apatite type structure occupies a significant place because of its electrical properties, as ionic conductor. In many cases, neodymium silicates are obtained by high-temperature synthesis, above 1400 °C. In our work the formation of Nd 9.33 Si 6 O 26 in silica matrix is shown at lower temperatures. By XRD method phase transformations in composites neodymium oxide - fumed silica with various molar ratios of components in the range of 1:1 to 1:20 were studied. With involvement of elemental analysis and electrical measurements, the formation of neodymium silicate with an apatite type structure was found in all the samples starting at the temperature of 920 °C. Formation of neodymium mono- or disilicate (Nd 2 SiO 5 or Nd 2 Si 2 O 7 ) is observed only at temperatures around 1400 °C with a stoichiometric ratio of neodymium and silicon oxides (1:1 or 1:2). In our opinion, Nd 9.33 Si 6 O 26 is an intermediate phase in the formation of other neodymium silicates in such composites. As the X-ray and elemental analysis showed, the structure of Nd 9.33 Si 6 O 26 differs from perfect by larger values of the parameters of hexagonal unit cell and much smaller factor of site occupation of 4f neodymium atoms. The composite obtained by annealing of oxides Nd 2 O 3 and fumed SiO 2 with a ratio of 1:20 at 1050 °C for 4 hours has an ionic conductivity on oxygen with specific conductivity value of 10 –3 –10 –4 Ohm –1 cm –1 in the temperature up to 200 °C as indicated by the linearity of this dependence. The composite Nd 9.33 Si 6 O 26 – SiO 2 with ratio of initial oxides 1:20 also exhibits photoluminescent properties due to the multiband absorption spectrum in the UV and visible region in ranges about 200, 600, 800 nm.