We have studied the effect of mechanical activation in lead ferroniobate synthesis on the formation of perovskite and pyrochlore phases during both mechanochemical synthesis and subsequent firing. It has been shown that, during mechanical activation, the first to form is the perovskite structure. During subsequent sintering of the material, the pyrochlore structure begins to form as well. As the firing temperature is raised to 650–750°C, the perovskite structure is again formed. We provide explanation for this process.

It has been shown that mechanical activation of a boehmite + lithium carbonate mixture with an Al : Li atomic ratio of 5 : 1 in an AGO-2 planetary activator at a centrifugal acceleration of 40g and milling times from 1 to 10 min and subsequent heat treatment of the mechanically activated mixture for 2 h at 900°C ensure the formation of fine-particle phase-pure lithium pentaaluminate with a specific surface area from 15 to 25 m2/g. We consider a scheme of the processes involved in the mechanically stimulated thermal synthesis of lithium pentaaluminate.

Valence states of iron and tantalum ions in eight ceramic compounds with a perovskite structure A(x)B(y)Ta(z)O(3+sigma) (A = Pb, Ba, Sr, Ca; B = Fe, Sc) were studied, including the compounds A(x)Fe(y)Ta(z)O(3+sigma), (A = Ba, Sr, Ca) annealed in a reducing atmosphere of CO. In a number of samples, the presence of Fe2+ ions was detected along with Fe3+. Relative fractions of the Fe2+ and Fe3+ ions were obtained by a full-profile fitting of the Fe2p X-ray photoelectron spectra (XPS) by superposition of experimental spectra of Fe2+ and Fe3+ ions, and by the Mossbauer spectroscopy method. The presence of Ta4+ ions along with Ta4+ ions was detected. The samples subjected to high-temperature annealing in the atmosphere of CO contain only Ta4+ ions. A modification of a standard methodology of the XPS determination of elemental compositions is proposed for the cases when the O1s-spectra have high-energy "tails"; it is based on ensuring the electrical neutrality of the samples. Changes in the elemental and ionic composition of the samples reflect the effect of the annealing of samples in a reducing atmosphere of CO.

— We have studied the effect of mechanical activation of a boehmite + lithium carbonate mixture in an AGO-2 planetary activator on phase transformations during heat treatment in air. The results demonstrate that heat treatment of the starting boehmite + lithium carbonate mixture leads to the formation of γ-Al 2 O 3 as a reaction intermediate, which reacts with lithium carbonate to form α-LiAlO 2 . Heat treatment of the activated mixture leads to the formation of gamma-aluminum oxide and an unidentified intermediate phase, presumably, metastable lithium aluminate, which transforms into α-LiAlO 2 at temperatures above 500°C. We have proposed a possible mechanism of the formation of this phase, which involves exchange of protons of boehmite with lithium cations, followed by the release of water and carbon dioxide.

The possibility of synthesis of nanodispersed composites Fe3O4@M(II)-Fe layered double hydroxides (M = Mg, Ni) is shown by mechanical processing a mixture of solid salts M(II) (M = Mg, Ni), Fe(II) and Fe(III) with solid sodium hydroxide, followed by washing the reaction products with water. The formation of magnetite in the composite occurs due to the interaction of salts of ferrous and trivalent iron with sodium hydroxide, in turn, the formation of layered double hydroxides due to the interaction of salts of divalent metals (M = Mg, Ni) and ferric salts with sodium hydroxide. It was exhibited that the prepared nanodispersed composites can be used as sorbents for the deep purification of aqueous solutions from As(III).

Recently we have found out that high-energy mechanical activation during mechanochemical synthesis stimulates disordering of Yb3+ and Nb5+ cations in the PbYb1/2Nb1/2O3 (PYN) ceramics. However, one could expect a contamination of thus obtained ceramics by iron as the planetary mill AGO-2 with both jars and balls made of the stainless steel was used for mechanical activation. To elucidate the effect of iron doping on the compositional ordering of PYN, in the present work several (1 − x)PYN–xPbFe1/2Nb1/2O3 (PYN–xPFN) solid solution compositions have been fabricated by both the usual solid-state synthesis and by high-energy mechanochemical synthesis and their structure and properties were compared. Basing on these data the (x, T)-phase diagrams for the PYN – xPFN solid solutions fabricated by both methods were constructed. It was found out that the difference in the lattice parameters values and dielectric properties of ceramics fabricated by different methods are partially due to the formation of the (1–x)PYN–xPFN solid solutions with PFN content larger than nominal one and partially due to the effect of high-energy mechanical activation.

— We have found conditions for the synthesis of fine-particle phase-pure α-LiAlO 2 via heat treatment of a mechanically activated mixture of gibbsite and lithium carbonate in air. The results demonstrate that, to synthesize α-LiAlO 2 , the mechanical activation of the reaction mixture should cause no gibbsite amorphization and heat treatment in air should be performed in the range 650–700°C.

Recently we found out that compositional ordering degree s of Yb3+ and Nb5+ ions in PbYb1/2Nb1/2O3 (PYN) ceramics can be varied by means of high-energy mechanical activation. In the present work dielectric and X-ray diffraction studies of the three obtained PYN ceramic samples with differing s values have been carried out in a wide temperature range. The highly disordered (s approximate to 0) sample appeared to be cubic in the 20-350 degrees C range and exhibited a diffused and frequency-dependent permittivity maximum at T-m approximate to 80 degrees C. Samples with s = 0.69 and 0.82 were orthorhombic at room temperature and exhibited non-diffused and frequency-independent permittivity maximum at T-m approximate to 170 and 250 degrees C respectively. However even in the most ordered PYN sample (s approximate to 0.82) cubic paraelectric and orthorhombic antiferroelectric phases coexist in the 190-300 degrees C temperature range.

Magnetic composites Fe3O4/layered double hydroxides (LDH) with a molar ratio of Fe3O4/LDH=1 were synthesized using the “soft” mechanochemical processing. The molar ratio M2+/Fe3+ (M2+ is Mg or Ni) in LDH was 2, 3 and 4. The synthesis was carried out in a mortar via the solid-state interaction between NaOH and salts mixtures containing the components necessary for the synthesis of both Fe3O4 and LDH. The feature of the proposed method is the simultaneous formation of the magnetic constituent Fe3O4 and the LDH phase in the reaction medium. The sorption properties of the obtained materials towards As(III) were investigated

The influence of the conditions of preliminary mechanical activation of a mixture of gibbsite and lithium carbonate in a planetary-type activator and the conditions of subsequent heat treatment on the phase composition of lithium aluminates is studied. It is shown that for the formation of γ-LiAlO2 it is necessary that at the stage of mechanical activation of the mixture an almost complete amorphization of aluminum hydroxide occurs, and the air heat treatment is carried out at a temperature above 750 °C. Thermal treatment of a mechanically activated mixture in the atmosphere with the partial water vapor pressure of below 1 Pa allows the synthesis of γ-LiAlO2 without significant amorphization of aluminum hydroxide at above 600 °C. For the synthesis of α-LiAlO2 preliminary mechanical activation should not lead to the amorphization of aluminum hydroxide, and the process of heat treatment in the air should be carried out at temperatures below 700 °C. The mechanism of formation of highly dispersed lithium aluminates during mechanical activation and subsequent heat treatment of a mixture of gibbsite and lithium carbonate is discussed.

It was shown that mechanochemical activation of a mixture of gibbsite and lithium carbonate in a ball mill for 2-4 h, followed by heat treatment of activation products in air at 650 degrees C, allowed obtaining highly dispersed monophasic alpha-LiAlO2 with a specific surface area more than 10 m(2)/g.

Recently we have found out that high-energy mechanical activationmechanical activation during mechanochemical synthesis stimulates disordering of Yb3+ and Nb5+ cations in the PbYb1/2Nb1/2O3 (PYN)PbYbNbO (PYN) ceramics. However, one could expect a contamination of thus obtained ceramics by iron as the planetary mill AGO-2 with both jars and balls made of the stainless steel was used for mechanical activationmechanical activation. To elucidate the effect of iron doping on the compositional orderingcompositional ordering of PYNPYN, in the present work several (1 − x)PYN–xPbFe1/2Nb1/2O3 (PYN–xPFN)(1 − )PYN–PbFeNbO (PYN–xPFN) solid solution compositions have been fabricated by both the usual solid-state synthesis and by high-energy mechanochemical synthesis and their structure and properties were compared. Basing on these data the (x, T)-phase diagrams for the PYN – xPFNPYN–xPFN solid solutions fabricated by both methods were constructed. It was found out that the difference in the lattice parameters values and dielectricdielectric propertiesdielectric properties of ceramics fabricated by different methods are partially due to the formation of the (1–x)PYN–xPFN(1 − )PYN–PFN solid solutions with PFNPFN content larger than nominal one and partially due to the effect of high-energy mechanical activationmechanical activation.

High-energy mechanical activation of the starting oxides was found to reduce dramatically or even suppress the frequency shift of the dielectric permittivity maximum of ceramic ferroelectrics-relaxors Pb2InNbO6 and Pb2InTaO6 sintered from the mechanochemically synthesized nanopowders. At the same time, the heights of the dielectric permittivity maxima for both compounds are substantially higher than those reported in the literature for similar ceramics obtained by usual solid state reactions route.

It has been found out that compositional ordering degree of the Yb3+ and M5+ (M - Nb, Ta) ions in Pb2YbMO6 ceramics and, correspondingly, both temperature and diffusion of antiferroelectric phase transition can be varied within a wide range by means of high-energy mechanical activation. In particular, disordered modifications of Pb2YbMO6 (M - Nb, Ta) were obtained without using any additives for the first time.

It was found out that compositional ordering degree S of Yb3+ and Nb5+ ions in PbYb1/2Nb1/2O3 ceramics and correspondingly both the temperature and diffusion of antiferroelectric phase transition can be varied within a wide range by means of high-energy mechanical activation. In particular, for the first time disordered PbYb1/2Nb1/2O3 ceramics exhibiting relaxor-like dielectric properties was fabricated without the use of any additives. For the most ordered PbYb1/2Nb1/2O3 samples (S ≈ 0.82), the coexistence of cubic paraelectric and orthorhombic antiferroelectric phases in a temperature range 190–300 °C was revealed.