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The preparation of platelike NaNbO3 grains via single-step molten salt synthesis using Bi2O3, Na2CO3, Nb2O5, and NaCl as reactants was examined. When a new alumina crucible was used, platelike NaNbO3 grains were obtained, but a repeatedly used alumina crucible resulted in irregularly shaped NaNbO3 grains. When a platinum crucible was used, even NaNbO3 could not be obtained. Addition of alumina substrates and alumina granules to the reaction mixture in the platinum crucible resulted in the formation of platelike NaNbO3 grains and second-phase grains. The second-phase grains, which were composed of Al2O3, Bi2O3, Na2O, and Nb2O5 and had a pyrochlore structure, could be removed by sieving. The second phase acted as a scavenger for Bi2O3 and hence, the possibility of using another scavenger was attempted. The new scavenger was a mixture of Na2CO3 and Nb2O5, and using them, platelike NaNbO3 grains were successfully obtained with NaNb5Bi2O16 as a byproduct, which could then be removed by sieving.

The preparation of 〈1 1 1〉-textured Bi0.5Na0.5TiO3 (BNT) ceramics was attempted by the templated grain growth method. This method uses anisometric grains as the template for texture development. In this work, plate-like BaTiO3 grains with the 〈1 1 1〉 direction perpendicular to the plate faces were used. A mixture of the plate-like BaTiO3 grains and equiaxed BNT grains was consolidated by tape casting to prepare green compacts in which the plate-like BaTiO3 grains were dispersed in the matrix of the BNT grains and were aligned with their plate faces parallel to the casting direction. The textured BNT ceramics could not be obtained by the sintering of the green compacts, because of the disappearance of the plate-like BaTiO3 grains by dissolution in the BNT grains. Several approaches were examined to obtain 〈1 1 1〉-textured ceramics. They included the use of plate-like (Sr, Ba)TiO3 grains as the template, the use of equiaxed grains of BNT–BaTiO3 and BNT–Bi0.5K0.5TiO3 solid solutions as the matrix, and the addition of excess Na2CO3 and Bi2O3 to form liquid phases. The only approach successful in obtaining the textured ceramics was the one involving the addition of excess Na2CO3. The excess Na2CO3 formed a liquid phase and promoted the formation of a shell of BNT grains around a plate-like BaTiO3 grain, prior to the dissolution of the BaTiO3 grain. The BNT shell had the same crystallographic orientation as the BaTiO3 grain and acted as the template for texture development.

The mechanisms of texture evolution in Bi0.5(Na,K)0.5TiO3 (BNKT) prepared by the templated grain growth method are examined using platelike SrBi4Ti4O15 and Al2O3 powders and SrTiO3 and Al2O3 single crystals as templates. These templates give rise to a 〈100〉 texture in the BNKT matrix. The mechanism of texture evolution is dependent on the template species. When SrBi4Ti4O15 and SrTiO3 are used, a new grain (terrace) forms between the matrix and the template grains. The terrace has the same crystallographic orientation as the template. The terrace grows at the expense of the matrix grains, resulting in texture evolution. For the Al2O3 template, no terrace forms between the matrix and the template grains. Instead, the matrix grains directly attach to the template surface. The formation of a phase boundary with a specific orientation gives rise to texture evolution for this template.

The effects of chemical composition on texture development have been examined for Bi0.5Na0.5TiO3 prepared by the reactive-templated grain growth method, using stoichiometric, Na-excess, and Na-deficient specimens. The highly textured material is obtained by heating the stoichiometric specimen at about 1100°C. Texture development is enhanced in the Na-excess specimen, and the highly textured specimen is hardly obtained for the Na-deficient specimen. The chemical composition affects the formation and growth stages of homo-template grains. Large homo-template grains form in the Na-excess specimen and grow at the expense of small matrix grains. These conditions of the preferential growth of homo-template grains are lost in the Na-deficient specimen because of the small size of homo-template grains and a high growth rate of matrix grains. The dependence of microstructure development on chemical composition is discussed based on the structure of the grain surface on an atomic scale.

It was found that platelike Al2O3 particles acted as a template for 〈100〉 texture in Bi0.5(Na1−xKx)0.5TiO3 (BNKT) grains prepared by the templated grain growth process. The degree of orientation was dependent on the potassium concentration in BNKT. The origin of texture development was discussed by examining the effect of potassium concentration on texture development through microstructure observation. Texture developed in the BNKT grains adhering to the Al2O3 plate faces, and the origin of texture development was the formation of the phase boundaries with thestructure. The degree of orientation was determined by the grain size of BNKT grains, porosity, and the efficiency of texture evolution. These factors were dependent on the potassium concentration, and the efficiency of texture evolution was determined by the energy of the phase boundaries with thestructure.

Dense BaTiO 3 ceramics with 〈1 1 1〉-texture were prepared by the TGG process. Platelike BaTiO 3 particles with their 〈1 1 1〉 direction perpendicular to the plate face were prepared by the reaction of platelike Ba 6 Ti 17 O 40 particles with BaCO 3 particles in molten NaCl. A green compact was composed of the aligned, platelike BaTiO 3 template particles dispersed in the matrix of small, equiaxed BaTiO 3 particles. Sintering caused densification and also the growth of template particles at the expense of matrix particles, resulting in texture development. Densification prior to grain growth was found to be necessary to obtain highly textured ceramics, and the effect of pre-sintering conditions on texture development was examined.

Dense, highly 〈110〉-textured BaTiO3 ceramics were prepared by the reactive-templated grain growth method. Needlelike TiO2 (rutile) particles with their needle axis parallel to 〈001〉 were used as reactive template particles. Slurry containing an equimolar mixture of TiO2 and BaCO3 was tape cast to form a green compact, in which TiO2 particles were aligned with their needle axis parallel to the casting direction. Calcination of the green compact changed TiO2 particles into BaTiO3 grains with their 〈110〉 direction parallel to the casting direction, for which the topotaxial relation ofwas responsible. Sintering yielded a dense, highly textured BaTiO3 compact.

The effect of template and matrix particle sizes on microstructure development was examined for BaBi4Ti4O15 textured by the templated grain growth method. Microstructure development was characterized by (1) the shape change of matrix particles from equiaxed to platelike, which resulted in texture development in the matrix phase, and (2) the formation of groups of large platelike grains with parallel alignment. The template particle size determined the size of grains in the final microstructure which was formed by process (2), and the matrix particle size influenced the rate of process (1).

Textured SrBi4Ti4O15 (SBT) ceramics were fabricated by the templated grain growth process to examine the effect of matrix particle size on texture development and densification. Texture was developed by the shape change of matrix grains from equiaxed to platelike and the alignment of their plate face parallel to that of template grains. The matrix particle size determined the number of platelike matrix grains with right orientation, and an increase in the matrix particle size increased the number of misoriented grains. Misoriented grains formed large pores, resulting in a low sintered density. It was concluded that small matrix particles were favorable for preparing dense, highly textured SBT ceramics.

The effect of sodium concentration on texture development in Bi0.5Na0.5TiO3 [BNT] bulk ceramics was examined. The 〈1 0 0〉-textured specimens were prepared by the reactive-template grain growth process using platelike Bi4Ti3O12 particles. Texture did not extensively develop in stoichiometric and Na-deficient BNT, but excess Na promoted extensive texture development together with densification. The role of excess Na was discussed based on the formation of a liquid phase.

Textured Bi 0.5 (Na,K) 0.5 TiO₃-BiFeO₃ ceramics were prepared by the reactive-templated grain growth process, using platelike Bi4Ti₃O₁₂ particles. The effects of chemical composition in Bi 0.5 (Na,K) 0.5 TiO₃ on texture development and densification were examined. Textured ceramics were obtained by using Bi 0.5 K 0.5 TiO₃ as an end member of the solid solution but densification was limited. Dense ceramics were obtained by using Bi 0.5 Na 0.5 TiO₃ but texture did not develop. Dense, textured ceramics were obtained by using Bi 0.5 (Na 0.5 K 0.5 ) 0.5 TiO₃.

Microstructure development in Bi 0.5 (Na 0.5 K 0.5 ) 0.5 TiO 3 prepared by a reactive-templated grain growth process was dependent on the sizes of platelike Bi 4 Ti 3 O 12 (BiT) and equiaxed TiO 2 particles used as starting materials. Calcined compacts were composed of large, platelike template grains and small, equiaxed matrix grains, the sizes of which were determined by those of the BiT and TiO 2 particles, respectively. Texture was developed by the growth of template grains at the expense of matrix grains during sintering, and a new mechanism of grain growth was proposed on the basis of microstructure observation. The grain growth rate was determined by the template and matrix grain sizes, and a dense ceramic with extensive texture was obtained using small BiT and TiO 2 particles.

Mesoporous ZnO nanosheets were successfully prepared by pyrolytic transformation of zinc carbonate hydroxide hydrate, Zn4CO3(OH)6·H2O. The nanosheets were initially formed as assemblies on glass substrates during chemical bath deposition (CBD) in aqueous solutions of urea and zinc acetate dihydrate, zinc chloride, zinc nitrate hexahydrate, or zinc sulfate heptahydrate at 80°C. It was key to induce heterogeneous nucleation of Zn4CO3(OH)6·H2O by promoting a gradual hydrolysis reaction of urea and controlling the degree of supersaturation of zinc hydroxide species. Morphology of Zn4CO3(OH)6·H2O was largely influenced by the anions present in the CBD solutions. The Zn4CO3(OH)6·H2O nanosheets were transformed into wurtzite ZnO by heating at 300°C in air without losing the microstructural feature.

Microstructure development was examined for BaBi4Ti4O15 prepared by the templated grain growth method, and the origin of texture development was discussed. The microstructure development in a compact composed of a platelike template and equiaxed matrix grains was characterized as follows: (1) the template grains thickened at an early stage; (2) the matrix grains changed their shape from equiaxed to platelike, and simultaneously, the plate faces aligned parallel to those of template grains; and (3) a group of large grains with mutually parallel alignment was formed by prolonged heating at high temperature. Texture developed during these microstructural changes, and process (2) made the greatest contribution toward texture development.

The properties of piezoelectric ceramics are enhanced by the development of crystallographic texture. One of the most convenient preparation methods for textured ceramics is the sintering of green compacts containing aligned anisometric particles. This review deals with the mechanisms of texture development by examining microstructure development in the compacts. The characteristics of microstructure development are summarized separately, depending on the preparation methods, which are divided into four groups: oriented consolidation of anisometric particles, templated grain growth, reactive-templated grain growth, and heterotemplated grain growth.

The densiflcation behavior and microstructure development were examined for Pb1-xBaxNb2O6 (x = 0.0, 0.15, and 0.30) with the low-temperature rhombohedral form. The rhombohedral form transformed to the high-temperature tetragonal form during sintering. The phase transformation increased the rate of grain growth, which influenced the microstructure development and densiflcation. The densiflcation proceeded partly before the phase transformation occurred, and the microstructure changed by the sequential formation of necks, chainlike grains, and equiaxed grains. The microstructure just after the phase transformation was determined by the microstructure just before the phase transformation. The chainlike and equiaxed grains changed to elongated and large equiaxed grains, respectively. Pore shape also changed.

The densification behavior and microstructure development of ZnO matrices containing rigid Zro2 inclusions were studied, with special emphasis on the effect of inclusion shape and size. The inclusions retarded the densification of the matrix, regardless of the inclusion shape and size. For large inclusions with diameters of 10 μm, dense regions developed between inclusion particles. The inclusion particles and dense regions formed a continuous network, which constrained the densification of the composites. The inclusion shape had a small effect on the development of dense regions. Severe retardation in densification was observed for compacts containing inclusions with diameters of 10 μm. In these cases, dense regions between inclusion particles did not develop. The formation of the continuous network cannot be applicable to small inclusions as an origin of retardation of densification.

Bulk BaTiO3 ceramics with 〈111〉-texture have been prepared by the modified templated grain growth method, using platelike Ba6Ti17O40 particles as templates, and the mechanism of texture development is examined. The Ba6Ti17O40 particles induce the abnormal growth of BaTiO3 grains, and a structure similarity between {001} of Ba6Ti17O40 and {111} of BaTiO3 gives 〈111〉-texture to abnormally grown BaTiO3 grains. Thus, the 〈111〉-texture develops in the BaTiO3 matrix. The use of platelike Ba6Ti17O40 particles has been extended to a 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 matrix, but the matrix phase is decomposed by extensive chemical reactions between the matrix and template phases.

The mechanisms of texture development were examined in the 〈0 0 1〉-textured bismuth layer-structured ferroelectrics (BLSF) prepared by the templated grain growth (TGG) method using BLSF templates with the composition different from that of the matrix. The formation and growth of layers of matrix grains on the templates were main mechanism for the texture development. Another mechanism of texture development was the formation of face-to-face contact between platelike template grains and matrix grains grown to be platelike.

Grain-oriented Bi0.5(Na0.85K0.15)0.5TiO3-Pb(Zr1−xTix)O3 (BNKT-PZT) ceramics were prepared via the reactive templated grain growth method, using platelike Bi4Ti3O12 particles. Factors that determine the degree of orientation were examined. Prereacted PZT gave a larger degree of orientation than PZT raw materials (PbO, ZrO2, and TiO2) in the 75BNKT-25PZT (x= 0.5) system. Increases in the titanium concentration in the PZT of the 75BNKT-25PZT system and in the BNKT concentration in the yBNKT-(100 −y)PZT (x= 0.5) system increased the degree of orientation. The direction of material transport between BNKT and PZT was important to obtain ceramics with a large degree of orientation.

Oxyfluoride glass-ceramic thin films of nominal 90SiO2⋅10(Ba1−xEu x )MgF4 compositions were prepared by sol–gel method starting from mixtures of metal trifluoroacetates and silicon alkoxide precursor solutions. Films were deposited on silica glass substrates by spin-coating and heating at 750°C. Eu2+ ions were preferentially incorporated into BaMgF4 nanoparticles, which were dispersed in the silica glass matrix. The films exhibited broad-band blue photoluminescence (PL) in response to the ultraviolet light excitation. Addition of N,N-dimethylformamide to starting coating solutions resulted in a porous microstructure of the heat-treated films. Efficient UV excitation was promoted due to the Rayleigh scattering in the porous films; thereby the PL emissions could be strongly enhanced.

Pr 3+ -doped YF 3 (orthorhombic), YO 0.80 F 1.40 (orthorhombic), YOF (rhombohedral), and Y 2 O 3 (cubic) films were synthesized on quartz-glass substrates through pyrolysis of a single-source trifluoroacetate precursor at temperatures between 400° and 900°C in air. Phase-selective deposition was achieved by controlling heating temperature and time. YF 3 , which formed first from the precursor, was transformed to YO 0.80 F 1.40 , YOF, and Y 2 O 3 . Photoluminescent properties of Pr 3+ -doped films were examined using ultraviolet excitation. An intense green photoluminescence was observed in the YOF:Pr 3+ film, which was deposited at 700°C, through an efficient charge transfer (O 2 -Pr3 + ) excitation.

Nanocrystalline zinc titanate (ZnTiO3) was synthesized at low temperatures through the combination of a sol–gel processing and a polymer binder method. ZnTiO3 powders of ∼5 nm in size were obtained by heating pastes, which were composed of a Zn-Ti methanolic solution containing acetylacetone and an organic polymer binder, at 500°C in air. Thermal decomposition behavior of the pastes was analyzed by thermogravimetry-differential thermal analysis. Crystallinity of ZnTiO3 was examined by transmission electron microscopy. The BET measurement revealed that the powders had a relatively high specific surface area of 106 m2/g.

Bi0.5Na0.5TiO3 (BNT) and 0.94Bi0.5Na0.5TiO3·0.06BaTiO3 (BNT–BT) bulk ceramics with extensive 〈100〉 texture were prepared by the reactive-templated grain growth method, using platelike Bi4Ti3O12 (BIT) particles as templates for BNT. Calcined compacts were composed of matrix grains with random orientation and 〈100〉-oriented grains transformed from aligned BIT particles, and the texture developed by the growth of oriented grains during sintering. Ceramics with extensive texture were obtained by using the starting mixture containing the maximum concentration of platelike BIT to form the maximum volume fraction of oriented grains.

Porous metal oxide (Co3O4, NiO, or ZnO) films were fabricated by a self-template method using layered hydroxide metal acetates (LHMA; metal = Co, Ni, or Zn) as templates. LHMAs were initially grown on glass substrates through a chemical bath deposition in methanolic-aqueous solutions of metal acetates at 60°C. The template films had a unique, nest-like morphology consisting of interlaced flake-like particles as a result of two-dimensional crystal growth of LHMAs in supersaturated solutions. The templates were successfully converted into porous Co3O4, NiO, or ZnO films by heating at 500°C for 10 min in air without microstructural deformation.

The mechanism for texture development in bismuth layer-structured ferroelectrics prepared by the templated grain growth method was examined using template and matrix grains with different chemical compositions. The template particles used were platelike Bi4Ti3O12 and Ba6Ti17O40 for SrBi4Ti4O15-matrix composites and platelike Ba6Ti17O40 and Sr3Ti2O7 for BaBi4Ti4O15-matrix. The 〈001〉-texture developed in all composites examined. The origins of texture development were the growth of matrix grains to be platelike and the formation of face-to-face contact between the template and matrix grains and also between matrix grains.

Polycrystalline Pb(Zr, Ti)O3 (PZT) ceramics with 〈111〉-texture were prepared by the templated grain growth (TGG) method using the platelike Ba6Ti17O40 (B6T17) particles as templates. Textured PZT was obtained by sintering of green compacts containing matrix PZT, aligned B6T17, and excess PbO. Excess PbO formed a liquid phase and promoted the dissolution of PZT grains and the precipitation on B6T17 grains. A similarity of the arrangement of ions on (001) of B6T17 and (111) of PZT gave 〈111〉-texture to matrix PZT.

Perovskite-type barium lithium fluoride (BaLiF3) was synthesized by pyrolysis of metal trifluoroacetates. The reaction temperature necessary for producing a single-phase material was found to be 600°C, which was lower than that for a conventional solid-state reaction or a melting method. Eu-doped BaLiF3 was also prepared and characterized to examine the suitability of trifluoroacetates for precursors in synthesizing homogeneous complex metal fluoride materials. It was demonstrated that trivalent Eu3+, which was used as acetate for a starting material, was reduced to divalent Eu2+ in the pyrolysis process of BaLiF3, as indicated by a broad blue emission due to an allowed 4f65d→4f7 transition at 408 nm with a ultraviolet excitation at 254 nm. The concentration quenching of the blue emission occurred at 5 at% of Eu in BaLiF3, indicating that Eu was homogeneously dispersed in the BaLiF3 host lattice. Mechanisms of the formation and reduction process of BaLiF3 were discussed based on pertinent chemical reactions.

Nanocrystalline ZnO particles were prepared from alcoholic solutions of zinc acetate dihydrate without using base such as NaOH or LiOH through a colloid process carried out at a low temperature of 60°C. A comparative study of chemical reactions from zinc acetate dihydrate to ZnO was made using different types of monool solvents, i.e. methanol, ethanol, and 2-methoxyethanol. It was revealed that layered hydroxide zinc acetate was formed as an intermediate and its transformation into ZnO was a key reaction step in any of the solutions. Reaction time necessary for the precipitation of ZnO was greatly influenced by the solvents used. Methanol was useful for the preparation of the ZnO nanoparticles, which were chemically pure in terms of cation impurities and exhibited green photoluminescence by the ultraviolet excitation.

Crystallographically textured ferroelectric and piezoelectric ceramics are prepared by tape casting of slurries containing powder particles with shape anisotropy. This paper describes the overview of these methods and the application of reactive-templated grain growth (RTGG) method to (100)-textured Bi 0.5 Na 0.5 TiO 3 (BNT) and 96Bi 0.5 Na 0.5 TiO 3 -6BaTiO 3 (BNT-BT) ceramics.

Luminescent rare-earth oxyfluoride materials were prepared by a sol-gel method using trifluoroacetic acid as a fluorine source. Crystalline (La, Eu)OF powders and thin films were obtained by heating gels at typically 600–800°C. Transparent SiO2-LaOF glass-ceramic thin films were also prepared by mixing the trifluoroacetate sols and silica sols, spin-coating on silica glass substrates and heating at temperatures 600–900°C. Eu3+ ions doped in the oxyfluoride materials exhibited a strong red 5D0 → 7F2 emission (611 nm) by a charge-transfer (O2−-Eu3+) excitation with ultra-violet radiation (265 nm). It was strongly suggested that the Eu3+ activators were preferentially incorporated into the crystalline LaOF phase in the SiO2-LaOF glass-ceramics.

Nanocomposite thin films where ZnGa2O4 nanoparticles were dispersed in fluorides, MgF2 or LaF3, were prepared by a sol-gel method using metal acetates and nitrates as starting reagents and trifluoroacetatic acid as a fluorine source. ZnGa2O4 and the fluorides such as MgF2 and LaF3 were formed simultaneously after the heat treatment of the spin-coated gel films as evidenced by X-ray diffraction. The films were transparent in the visible region. With decreasing the ZnGa2O4 content, absorption edges showed blue-shift. All the films exhibited a broad-band blue emission around 430 nm by ultra-violet excitation at 254 nm. The intensity of the blue emission in the PL spectra increased with decreasing the ZnGa2O4 content. These phenomena were attributed to the quantum size effects (the increased band-gap) and the surface effects (the increased luminescent center) in the nano-sized ZnGa2O4. The mechanism of the emission was discussed in view of surface states in the oxide nanoparticles.

Bi0.5(Na1-xKx)0.5TiO3 (BNKT) bulk ceramics with a preferred orientation were prepared using the reactive templated grain-growth method with platelike Bi4Ti3O12 particles as templates for BNKT. The potassium concentration (x value) had a large effect on the degree of orientation, and highly oriented ceramics were obtained for the specimens with x= 0.10 and x= 0.15, whereas the specimen with x= 0.00 had a small degree of orientation. Increased potassium concentration from x= 0.00 to x= 0.15 decreased the grain-growth rate and changed the grain shape from irregular to cubic. These factors were responsible for the increased degree of orientation.

Needlelike Sr0.5Ba0.5Nb2O6 powder particles were prepared from SrCO3, BaCO3, and Nb2O5 in the presence of a mixture of molten SrCl2 and BaCl2. When the composition of the mixture of oxide and carbonate was fixed to be SrCO3:BaCO3:Nb2O5 = 1:1:2, the phase and morphology of the product particles were dependent on the composition of molten salt. The exchange reaction, BaO + SrCl2 = BaCl2 + SrO, enriched Sr in the oxide phase. The relation between the compositions of the salt mixture and the reaction product was determined, and needlelike Sr0.5Ba0.5Nb2O6 particles were obtained by using the molten salt containing 18 mol % SrCl2.

LaNiO3(100)/CeO2(100)/Si(100) as a metal/insulator/semiconductor heterostructure was prepared by a sol-gel method with a spin-coating technique. The structure of each oxide layer was investigated by out-of-plane and in-plane X-ray diffraction analyses. The high degree of {100} -orientation of the CeO2 layers was obtained with higher heat treatment temperatures, 600-700°C. The in-plane measurements revealed that the CeO2 layers had a nonepitaxial structure in spite of the deposition on the Si(100) substrates with good lattice compatibility. The LaNiO3 layers on the CeO2(100)/Si(100) also exhibited the preferential {100} -orientation without epitaxy. The crystallinity of the {100} -oriented grains in the LaNiO3 layers was higher than that in the CeO2 layers. The occurrence of the orientation was discussed in view of the interfacial energies at each interface.

Zinc oxide thin films doped with Li and Mg were prepared by the sol-gel method, and effects of doping on microstructure and electrical properties were examined. The doped films exhibited c-axis-orientation after final heating at 500°C for 30 min in flowing oxygen. The ZnO crystallite size increased by doping and the surface of the films became rougher. The current density of the films was reduced by doping probably due to the formation of acceptor levels (Li-doping) and the reduction of oxygen defects (Mg-doping). The film with a nominal composition of Zn0.85Li0.10Mg0.05O showed the lowest current density of 1.7×10−6 A cm−2 in the present study.

A polycrystalline BaTiO3 bulk ceramic with a preferred ‹111› orientation was fabricated by the reactive templated grain growth method. A green compact was made by tape-casting of slurry containing plate-like Ba5Ti17O40 template particles and BaCO3 powder. Single phase BaTiO3 was obtained by calcining the green compact at 1000°C. The calcined compacts were sintered between 1250 and 1400°C. The degree of orientation increased with an increase in the sintering temperature. Growth of ‹111›-oriented BaTiO3 grains originated from the Ba6Ti17O40 particles is responsible for the increase in the degree of orientation.

The products of reaction between Pb(Zr0.53Ti0.47)O3 (PZT) and glasses in the PbO-SiO2 and PbO-B2O3-SiO2 systems at 850°C were studied using powder and bulk PZT samples. A reaction zone was formed between bulk PZT and the glass. The microstructure of the reaction zone changed with the amount of PZT dissolved in the glass phase, which was dependent on the activity of PbO in both the glass phase and PZT. When the amount of dissolved PZT was small, as in the reaction between PZT and 60mol% PbO⋅40mol% SiO2 glass, the glass phase penetrated into grain boundaries of PZT, and no solid reaction product was formed. When the amount of dissolved PZT was intermediate, as in that between PZT and 40mol% PbO⋅60mol% SiO2 glass, the glass phase penetrated into the PZT pellet and ZrO2 particles were precipitated in the glass phase. When the amount of dissolved PZT was large, as in those between PZT and 60mol% PbO⋅20mol% B2O3⋅20mol% SiO2 glass and 40mol% PbO⋅30mol% B2O3⋅30mol% SiO2 glass, the reaction zone was formed, which was composed of Ti-rich PZT and ZrO2 particles dispersed in the glass phase.

Densification behavior and microstructural characteristics were examined for BaTiO 3 containing 0.25-2.00 mass% Li 2 Si 2 O 5 . Li 2 Si 2 O 5 lowered the sintering temperature of BaTiO 3 . The optimum concentration to obtain high density was 1 mass%. A concentration smaller than the optimum value did not effectively lower the sintering temperature, while a larger concentration resulted in the formation of inhomogeneous microstructure. There was an optimum sintering temperature to obtain compacts with maximum density. Extensive grain growth occurred above the optimum temperature. The grain boundary phase, which was a liquid phase at the sintering temperature, contained TiO 2 -rich particles, whose distribution was non-uniform. The formation mechanisms of such microstructure were discussed.

We fabricated LaNiO 3 (LNO) thin films on SiO 2 glass, (100) SrTiO 3 (STO), (100) Si and CeO 2 -covered (100) Si substrates by the sol–gel method. The deposited films were heat-treated at 700°C with various conditions, duration and atmosphere. Preferentially (100)-oriented, polycrystalline LNO films were obtained on STO and Si. It was also found that orientated films could be formed even on SiO 2 glass and CeO 2 -covered (100) Si substrates by altering the heating process. We investigated a relationship between the resistance and the crystallite size of the LNO films. The sheet resistance of LNO decreased with increasing crystallite size of LNO. The resistivity and sheet resistance of LNO/STO at 300 K were 340 μΩ·cm and 33.8 Ω/□, respectively, and those values of LNO/CeO 2 /Si at 300 K were 460 μΩ·cm and 28.8 Ω/□.

The products of reaction between Pb(Zr0.53Ti0.47)O3 (PZT) and PbO-B2O3 glasses at 850°C were studied using powder and bulk PZT samples. PZT dissolved in glass phase and solid products were precipitated. The reaction zone composed of glass phase and solid products was formed between bulk PZT and glass. As the B2O3 content in the glass increased, the amount of dissolved PZT and the thickness of reaction zone increased. When glasses with 40 and 60mol% B2O3 were used, the solid products were Ti-rich PZT and ZrO2 (ZrO2-TiO2 solid solution), which were expected from the phase diagram of the PbO-ZrO2-TiO2 system. When a glass with 80mol% B2O3 was used, the solid products were ZrO2 and TiO2, which were supposed to be formed by non-equilibrium reaction sequences. The microstructure of the reaction zone depended on the chemical composition of glass, indicating that the solubility of constituent oxides of PZT was dependent on glass composition.

Metal fluoride films were prepared from trifluoroacetate sols by a spin-coating method. Effects of preparation conditions on the deposition of fluoride films have been examined in order to control the thickness and the refractive index of the films. It was suggested that the fluoride was formed by the thermal decomposition of the trifluoroacetate sols generating gaseous phases such as (CF3CO)2O, CO and CO2. This reaction mechanism seemed to largely effect the deposition of the fluoride films in terms of the formation of pores. Characteristics of the fluoride films could be changed by varying the heat treatment. The refractive index of the MgF2 films decreased with increasing heating temperature, which might result from the increased porosity of the films. Drying the film before the heat treatments was effective in the control of the refractive index.

The interfacial reaction between Ag and NdBa2Cu3O7-δ (Nd123) was examined from the viewpoint of low-temperature processing of superconducting materials. The incongruent melting temperature of an Nd123 sample was measured to be as low as 960°C in N2. Addition of 10 mass% of Ag to Nd123 decreased further the incongruent melting temperature of Nd123 to 920°C. By a model experiment using an Ag pellet embedded in Nd123, it was revealed that an Ag-dissolved (Ba,Cu)-rich phase was formed near the interface with Ag. Based upon these results, Ag-added Nd123 ceramic samples were prepared by the partial melting process at temperatures below the melting point of Ag, 960°C. Superconducting properties of the ceramic samples were improved by the addition of Ag.

We tried to prepare the mercury-based superconductor, HgBa 2 Ca 2 Cu 3 O 8+δ (Hg1223), under highly oxidizing atmosphere using a high pressure technique. Samples containing Hg1223 as the main phase with T C =90–122 K were obtained. CuO and a new phase were included in the samples as impurities. The a -axes of the samples were shorter than the values ever reported for Hg1223 with T C =135 K. These results suggest that our Hg1223 samples had excess hole concentrations, i.e. they are over-doped. The irreversibility field ( B irr ) was measured for two samples with T C =118 and 94 K. They had almost the same normalized temperature (1− T/T C ) dependence of B irr .

A novel sol–gel process for silica/fluoride composites is described. Crystallization of LaF3 in the sol–gel silica has been investigated. Dry silica gels containing La3+ and trifluoroacetate ions (CF3COO−) were produced from tetramethylorthosilicate (TMOS), methanol, dimethylformamide, lanthanum acetate, trifluoroacetic acid, water and nitric acid. By heating the gels at temperatures above 300°C, LaF3 microcrystals with a size of 10–30 nm were formed in the silica matrix. IR, XPS and TG-DTA analyses suggested that CF3COO− ions are coordinated to La3+ ions in the sols and the dried gels, leading to the formation of LaF3 by the thermal decomposition at elevated temperatures.

In an attempt to obtain dense PbNb 2 O 6 ceramics, sintering experiments were conducted using starting powders with various particle sizes and different modifications (rhombohedral and orthorhombic structures). During sintering of rhombohedral powders, the phase transformation to the tetragonal phase promoted grain growth, resulting in poor densification. Sintering of orthorhombic powders, however, yielded dense ceramics through suppression of the phase transformation. Based on these results, ceramics with various densities and different microstructures were prepared, and their dielectric and piezoelectric properties were evaluated. The dielectric constant and Curie temperature were dependent on density, grain size, and crack density. Cracks and intragrain pores severely deteriorated the piezoelectric properties. Dense ceramics with the maximum coupling factors and piezoelectric strain constants were obtained by prolonged heating of a fine powder with orthorhombic structure.

Ag-doped NdBa2Cu3O7-δ superconducting ceramics were prepared by a sol-gel method. Ag was distributed uniformly in the sintered samples. The incongruent melting temperature of the NdBa2Cu3O7-δ samples prepared by our sol-gel method was lower than that of the samples prepared by the conventional powder method. The incongruent melting temperature was further decreased by doping with Ag. The authors consider that the incongruent melting is induced by reaction between NdBa2Cu3O7-δ and Ag. The superconducting transition width ΔT(ΔT=Tc(onset)-Tc(end)) was decreased by doping with Ag. The electrical resistivity of a 10mass% Ag-doped sample dropped sharply from 93K (Tc(onset)) and showed zero resistivity at 86K (Tc(end)).