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The results of comparative multifractal studies of the grain structure of different ceramic piezoelectric materials are presented. Hard and soft ferroelectric ceramic materials as well as materials...

X-ray diffraction (XRD) studies of the phases formed on the surface of the Li-doped PbFe0.5Nb0.5O3 (PFN) ceramics sintered under different conditions from the mechanically activated mixture of oxides and Li2CO3 have been carried out. At sintering temperatures exceeding 800°C a partial evaporation of PbO leads to the formation of pyrochlore Pb2Fe4Nb4O21 and lithium ferrites LiFeO2 and LiFe5O8 phases in the surface layer about 100 μm thick. An increase of the Neel temperature by more than 40 K, as compared to single crystal, was achieved in the mechanically activated PFN powder sintered at 600°C.

The effect of high-energy mechanical activation on magnetic phase transition temperature TM of PbFe0.5Nb0.5O3, PbFe0.5Ta0.5O3, and BaFe0.5Nb0.5O3 perovskites has been studied. Mossbauer studies have shown that TM values in all the perovskites studied can be changed substantially by mechanical activation and subsequent annealing. The increase of TM by 40-50 K, as compared to corresponding single crystals and ceramics sintered from the non-activated powders, was achieved in the mechanoactivated powders of both lead-containing and lead-free perovskites studied.

The effect of high-energy mechanical activation on dielectric and magnetic properties of PbFe1/2Ta1/2O3 (PFT) multiferroic was studied. Mossbauer studies have shown that the Neel temperature TN of the antiferromagnetic phase transition in PFT powders can be changed substantially by mechanical activation and subsequent annealing. The increase of TN by more than 70 K, as compared to PFT single crystal, was achieved in the mechanically activated PFT powder annealed at 700°C. Dielectric studies have shown that in contrast to ceramics obtained by usual sintering, PFT ceramics fabricated by sintering of the mechanoactivated powder does not show the relaxor-like behavior.

Optimal sintering temperature of PbFe1/2Nb1/2O3 (PFN) ceramics is 1120–1150°C, but ceramics sintered in this temperature range have low resistivity and high losses. Mechanochemical synthesis allows one to lower the optimal sintering temperature of PFN ceramics down to 1000°C, however dielectric losses remain high and the permittivity exhibits large frequency dispersion. In the present work it has been found that similar to the case of the routine solid state synthesis, Li doping enables one to reduce dramatically the losses of the PFN ceramics obtained by sintering the mechanochemically synthesized powders.

The double decoupling version of the thermodynamic integration procedure is applied to perform the molecular dynamical modelling of binding free energies of β-cyclodextrine (CD) with a number of organic ligands. Simulations for water solutions show a satisfactory agreement (within 1–2 kcal/mol) with the experimentally measured equilibrium binding constants. The values are also reported for the gas phase complexation of the same ligands, although no experimental data are available for such systems. These gas phase computations have revealed the large stabilisation effect for the CD complexes of ionic ligands. Only in this special case the attempt of a qualitative rationalising the obtained simulation data proved to be fairly successful. The problems specific for simulations for ionic ligands in water solution are discussed.

Ceramics of (1 − x)NaNbO3− (x)Na0.5Bi0.5TiO3 and (1 − x)NaNbO3 − (x)Sr0.5 NbO3 binary solid solutions exhibit strongly diffused permittivity maxima, when x exceeds a threshold value of about 0.15 and 0.1, respectively, but show weak frequency dispersion of permittivity and small frequency shift of the permittivity maximum temperature. Addition of LiNbO3 to these compositions increases the permittivity maximum temperature and greatly enhances the frequency dependence of both the permittivity maximum temperature and permittivity values.

The processes of the formation and evolution of grain structures in binary systems of solid solutions (1−x)NaNbO3-xCa2Nb2O7(Sr2Nb2O7), where 0 ≤ x ≤ 1, are discussed. The multifractal parameterization of the sections of grain boundaries was performed. A correlation between multifractal and electrophysical parameters of niobate ferroelectric ceramics was established. A possibility of the quantitative description of microstructures in the systems under study by means of multifractal ideas is shown. The results obtained were used for optimization of the processes of preparation of new ferroelectric materials.

A method of evaluating the spectral moments Ml 2k of the rotational correlation functions for the first- and second-rank tensors of rigid asymmetric top molecules is developed. It is based on the calculation of the coefficients of a Taylor series expansion of the vector and tensor orientational correlation functions about t = 0 with the help of angular momentum theory, and is applicable to a pair intermolecular interaction potential with arbitrary dependence on the angular variables. Equations for the second (Ml 2), fourth (Ml 4), and sixth (Ml 6) spectral moments are obtained as a demonstration of the ability of the method. The results for (Ml 2) and Ml 4 coincide with previously known values and the equation for Ml 6 is new. As particular cases, the theory contains the results for classical ensembles of symmetric tops, spherical tops, and linear molecules.