An analysis of the results of modern investigations into the field of producing nanocrystalline alumina ceramics is performed. It is shown that the prospects of creating competitive nanocrystalline ceramics, which are considered from the viewpoint of improving the structure and technology upon alloying, are associated with possibilities of activating ceramic powders during compaction and sintering due to the modification of the surface by the deposited alloying components.

Experimental results of depositions of thin Ti, La, Pb, Cd, Mn, Zr, and Y oxide films on the surface of a 50-μm-thick aluminum foil, used for manufacturing electrolytic capacitors by the pyrolysis method of salts of carboxylic acids, are presented. The obtained samples are characterized by capacitance values of 40 to 240 μF/cm 2 and electric strength values in an interval of 0.5 to 2 V, except for Ti oxides, whose samples have an electric strength of 2 to 8 V. The obtained capacitance and electric strength values are close to the values possessed by commercially produced aluminum foils with thicknesses of 70–107 μm having an aluminum oxide dielectric on the surface.

A method of metalorganic compounds pyrolysis for low-temperature (about 500–600 oC) synthesis of perovskites PbTiO3 and PbZrO3 was tested to obtain films of this structures on sapphire substrates. The qualitative and quantitative X-ray diffraction analysis (XRD) of the films was carried out. The analysis showed that films obtained at 550 oC contain perovskites PbZrO3 and PbTi3O7.

The nanograined thin films of undoped ZnO were synthesized by the wet chemistry method. Films consist of the equiaxial nanograins, and possess ferromagnetic properties. Structural investigations by the XRD and HREM reveal that the crystalline wurtzite grains do not contact each other and are completely surrounded by a layer of amorphous phase. It forms a kind of continuous foam-like network, where the amorphous intergranular phase amount could be increased by the synthesis parameters. Simultaneously, the saturation magnetization increases as well.

A method of metalorganic compounds pyrolysis for low-temperature (about 500-600 degrees C) synthesis of perovskites PbTiO(3) and PbZrO(3) was tested to obtain films of this structures on sapphire substrates. The qualitative and quantitative X-ray diffraction analysis (XRD) of the films was carried out. The analysis showed that films obtained at 550 degrees C contain perovskites PbZrO(3) and PbTi(3)O(7).

Pure ZnO thin films were obtained by the wet chemistry (“liquid ceramics”) method from the butanoate precursors. Films consist of dense equiaxial nanograins and reveal ferromagnetic behaviour. The structure of the ZnO films was studied by the high-resolution transmission electron microscopy. The intergranular regions in the nanograined ZnO films obtained by the “liquid ceramics” method are amorphous. It looks like fine areas of the second amorphous phase which wets (covers) some of the ZnO/ZnO grain boundaries. Most probably these amorphous intergranular regions contain the defects which are responsible for the ferromagnetic behaviour.

The pure ZnO thin films were deposited by the wet chemistry ('liquid ceramics') method from the butanoate precursors on the single-crystalline (102) sapphire substrates. The films annealed in air (550 degrees C, 24 h) after butanoate pyrolysis have pronounced texture, and they reveal the ferromagnetic behaviour. Argon annealed films (650 degrees C, 30 min) exhibit randomly oriented grains, where the ferromagnetism of these non-textured films is almost equal to that of bare substrate. In both cases the films consist of dense equiaxial nanograins with size similar to 20 nm. We observed that grain boundaries (GBs) and related vacancies are the intrinsic origin for RT ferromagnetism in polycrystals [Straumal et al., Phys. Rev. B 79, 205206 (2009)]. Present results demonstrate that not only the specific area of GBs in nanograined ZnO alone determines the ferromagnetic behaviour of ZnO. The GB character distribution (i.e. GB misorientation and orientation) is different in the textured and non-textured films. Most probably, the GBs with different character possess also different magnetic properties. The role of GBs, free surfaces and interfaces in ferromagnetic behaviour of GaN is discussed. In particular, their presence permits to increase the Mn solubility in GaN without precipitation of secondary ferromagnetic phases. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Dense nanograined pure and Mn-doped Zn1−xMnxO polycrystals with x ranging between 0.1–34 at. % were synthesized by the wet chemistry method from butanoate precursors. Pure and Mn-doped ZnO possesses ferromagnetic properties only if the ratio of grain boundary (GB) area to grain volume sGB exceeds a certain threshold value sth. The polycrystals in this work satisfy these conditions and, therefore, reveal ferromagnetic properties. The observed dependence of saturation magnetization on the Mn concentration shows an unexpected nonmonotonous behavior. The increase in saturation magnetization at low Mn concentration is explained by the injection of divalent Mn2+ ions and charge carriers into pure ZnO. The decrease in saturation magnetization between 0.1 and 5 at. % Mn can be explained by the increase in the portion of Mn3+ and Mn4+ ions. The second increase in saturation magnetization above 5 at. % Mn is explained by the formation of multilayer Mn segregation layer in ZnO GBs. The shape of the dependence of saturation magnetization on Mn concentration is different for the Mn-doped nanograined ZnO manufactured by different methods. It is most probably controlled by the topology of GB network (ferromagnetic GB foam) in the ZnO polycrystals.

The complete solubility of an impurity in a polycrystal increases with decreasing grain size, because the impurity dissolves not only in the crystallite bulk but also on the grain boundaries. This effect is especially strong when the adsorption layers (or the grain boundary phases) are multilayer. For example, the Mn solubility in the nanocrystalline films (where the size of grains is ∼20 nm) is more than three times greater than that in the ZnO single crystals. The thin nanocrystalline Mn-doped ZnO films in the Mn concentration range 0.1–47 at % have been obtained from organic precursors (butanoates) by the “liquid ceramic” method. They have ferromagnetic properties, because the specific area of the grain boundaries in them is greater than the critical value [B.B. Straumal et al., Phys. Rev. B 79 , 205206 (2009)]. The high-resolution electron transmission microscopy studies show that the ZnO nanocrystalline grains with the wurtzite lattice are separated by amorphous layers whose thickness increases with the Mn concentration. The morphology of these layers differs greatly from the structure of the amorphous prewetting films on the grain boundaries in the ZnO:Bi 2 O 3 system.

Nanograined (grain size 20nm) ZnO films with various Mn content (from 0 to 47at%) were synthesized by the novel wet chemistry method. The solubility limit for Mn was determined at 550°C. The lattice parameter c of the ZnO-based solid solution with wurzite structure ceases to grow at 30at% Mn. The peaks of the second phase (Mn3O4 with cubic lattice) become visible in the X-rays diffraction spectra at 30at% Mn. The same second phase appears in the bulk ZnO already at 12at% Mn. The recently published papers on the structure and magnetic behaviour of Mn-doped ZnO allowed us to obtain the size-dependence of Mn solubility in ZnO for the polycrystals and small single-crystalline particles. The overall Mn solubility drastically increases with decreasing grain size. The quantitative estimation leads to the conclusion that, close to the bulk solubility limit, the thickness of an Mn-enriched layer is several monolayers in GBs and at least two monolayers in the free surfaces.

Nanostructured conducting oxides are very promising for various applications like varistors (doped zinc oxide), electrolytes for the solid oxide fuel cells (SOFC) (ceria, zirconia, yttria), semipermeable membranes, and sensors (perovskite-type oxides). Grain boundary (GB) phases crucially determine the properties of nanograined oxides. GB phase transformations (wetting, prewetting, pseudopartial wetting) proceed in the conducting oxides. Novel GB lines appear in the conventional bulk phase diagrams. They can be used for the tailoring of properties of nanograined conducting oxides, particularly by using the novel synthesis method of liquid ceramics.

Nanostructured conducting oxides are very promising for various applications like varistors (doped zinc oxide), electrolytes for the solid oxide fuel cells (ceria, zirconia, yttria), semi-permeable membranes and sensors (perovskite-type oxides). Grain boundary (GB) phases crucially determine the properties of nanograined-oxides. GB phase transformations (wetting, prewetting, pseudopartial wetting) proceed in the conducting oxides. Novel GB lines appear in the conventional bulk phase diagrams. They can be used for the tailoring of properties of nanograined-conducting oxides, particularly by using the novel synthesis method of liquid ceramics.