Structure and paramagnetic centers of nanodisperse synthetic ZrSiO 4

Paramagnetic centers generated by the ionizing irradiation in the synthetic nanodisperse zirconium silicate modeling products of zircon destruction was investigated by ESR method. Synthesis of powders of zircon is made on zol-gel to a technique (specimen 1444) or from suspension (sp. 1445) solution of oxychloride of zirconium and silicate of sodium with the subsequent hydrothermal processing and crystallizing annealing at 1050 °C. Diagnostic of the substance was conducted by X-ray fluorescent method, quantitative X-ray phase analysis, infrared and Raman spectroscopy. The synthesized products contained 82-84% phase ZrSiO 4 and 16-18 % of the phases t-ZrO 2 and m-ZrO 2. A zirconium silicate phase in sp. 1445 is low-ordered with an effective size of crystallites of 10-20 nanometers, determined by modified Sherrer's method, and it is similar to crystal zircon in sp. 1444 with an average the sizes of crystallites of 75 nanometers. Ionizing irradiation of synthetic zircon leads to the formation of impurity-related paramagnetic Ti 3+ (g || = 1.9270, g = 1.9407) - and own SiO 33- (g z = 2.0056, g y = 2.0022, g x = 2.0002) -, SiO 45- (g || = 2.0021, g = 2.0007) - centers in grains volume, corresponding to their analogs in natural zircon crystals. Due to the nanodispersion of synthetic zircon, the paramagnetic centers are characterized by the lowered thermal stability. Ti 4+ ions integrate into the atomic positions of zirconium in equal concentrations independently of the degree of zirconium silicate dispersion. Broadening of the EPR lines of the radiation-induced paramagnetic Ti 3+-centers is a measure of crystallinity of the zircon lattice. The highly crystalline ZrSiO 4 synthetics also contained impurity electron paramagnetic centers with boron ions (g || = 1.9810, g = 1.9685) and unidentified impurity hole paramagnetic centers with g > 2.00. Perhaps, boron atoms and other impurity elements are captured in a zircon lattice from the surface at a stage of high-temperature crystallizational annealing with enlargement of initial semi-amorphous ZrSiO 4 nanoparticles. The own electron-hole SiO 33- - and SiO 45- -centers are formed in big concentration in synthetic semi-amorphous silicate of zirconium. The concentration of the radiation-induced centers reduces more than an order of magnitude at increasing the degree of crystallinity of zirconium silicate and the crystallite sizes from 19 to 75 nm. The parameters and temperature features of EPR spectra of SiO 33-- and SiO 45--centers indicate their localization in defective fragments of the zirconium silicate lattice. We think that these own defects are markers of the zircon lattice disordering. Results of our researches confirm the previous conclusions about the possibility of using EPR-characteristics of own defects SiO 33- and SiO 45- as "paramagnetic probes" of the structure of damaged natural zircon and its regeneration under thermal influences.