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The present work considers hydrogen generation from water using solar energy. The work is focused on the materials-related issues in the development of high-efficiency photo-electrochemical cells (PECs). The property requirements for photo-electrodes, in terms of semiconducting and electrochemical properties and their impact on the performance of PECs, are outlined. Different types of PECs are overviewed and the impact of the PEC structure and materials selection on the conversion efficiency of solar energy are considered. Trends in research in the development of high-efficiency PECs are discussed. It is argued that very sophisticated materials engineering must be used for processing the materials that will satisfy the specific requirements for photo-electrodes. An important issue in the processing of these materials is the bulk vs. interface properties at the solid/solid interfaces (e.g., grain boundaries) and solid/liquid interfaces (e.g., electrode/electrolyte interface). Consequently, the development of PECs with the efficiency required for commercialization requires the application of up-to-date materials processing technology. The performance of PECs is considered in terms of: • excitation of electron–hole pair in photo-electrodes; • charge separation in photo-electrodes; • electrode processes and related charge transfer within PECs; • generation of the PEC voltage required for water decomposition. This work also gives empirical data on the performance of PECs of different structures and materials selection. It is argued that PEC technology is the most promising technology for hydrogen production owing to several reasons: • PEC technology is based on solar energy, which is a perpetual source of energy, and water, which is a renewable resource; • PEC technology is environmentally safe, with no undesirable byproducts; • PEC technology may be used on both large and small scales; • PEC technology is relatively uncomplicated. According to current predictions, the production of hydrogen will skyrocket by 2010 (Morgan and Sissine, Congressional Research Service, Report for Congress. The Committee for the National Institute for the Environment, Washington, DC, 20006-1401, 28 April 1995). Consequently, seed funding already has been allocated to several national research programs aiming at the development of hydrogen technology. The countries having access to this PEC technology are likely to form the OPEC of the future.

This paper reports the transport kinetics of Mg in cubic yttria-stabilized zirconia (containing 10% mol of Y2O3 (10YSZ)) involving the bulk and the grain boundary diffusion coefficients. The diffusion-controlled concentration profiles of Mg were determined using secondary ion mass spectrometry (SIMS) in the range 1073–1273 K. The determined bulk diffusion coefficient and the grain boundary diffusion product may be expressed as the following functions of temperature, respectively: D= 5.7 exp[(−390 kJ/mol)/RT] cm2·s−1 and D′αδ= 3.2 × 10−15 exp[(−121 kJ/mol)/RT] cm3·s−1, where α is the segregation enrichment factor and δ is the boundary layer thickness. The grain boundary enhancement factor decreases with temperature from 105 at 1073 K to 103 at 1273 K.

The present paper considers the effect of oxygen partial pressure on the presence of point defects in calcium titanate (CaTiO3) at elevated temperatures at which a gas/solid equilibrium is reached. Defect models of undoped (CaTiO3) are considered within several regimes of oxygen partial pressures involving (i) extremely reducing conditions, (ii) reducing conditions, and (iii) oxidizing conditions, which are described by different charge-neutrality conditions. The mechanism of donor incorporation is considered in terms of both ionic and electronic charge compensation. It is shown that electronic and ionic charge compensations prevail at low and high p(O2), respectively.

This paper reports electrical properties of In2O3 thin film (100 nm) at elevated temperatures (667–1118 K) and under controlled oxygen activity. The present study, based on the measurements of electrical conductivity (EC) using the method proposed by van der Pauw, includes the following determinations: Dynamics of EC changes during gas/solid equilibration of the O2/In2O3 system; The dependence of EC on oxygen partial pressure dependence; The dependence of EC on temperature.

Electrochemical characteristics of photo-electrochemical cell (involving photo-anode made of TiO2 and Pt as cathode) were investigated during the light-on and the light-off regimes using the sunlight. Maximum photo-voltage of the open cell involving undoped TiO2 as photo-anode is 0.7 and 1.6 V without and with chemical bias (Δ pH=14.6), respectively. Application of ceramic Cr-doped TiO2 (involving 1 wt % of Cr2O3) as photo-anode results in a substantial decrease of the cell voltage (to 0.8 V ) despite the application of chemical bias.

Correction for ‘Growth mechanism of ceria nanorods by precipitation at room temperature and morphology-dependent photocatalytic performance’ by Zhao Liu et al., CrystEngComm, 2017, 19, 4766–4776.

To investigate excess-hydrolysis of titanium alkoxides, TiO2 powders were fabricated from titanium-tetra-isopropoxide using 6:1 and 100:1 H2O:Ti (r) ratios. Powders were dried and fired at a range of temperatures ( up to 800 C). Hydroxylation and organic content in powders were characterised using ATR-FTIR, laser Raman microspectroscopy, and elemental microanalysis; surface area and pore size distribution were evaluated using N2 gas adsorption; phase composition was analysed using XRD and laser Raman microspectroscopy; and crystallite size was evaluated by XRD, TEM and SEM. Results showed near-complete hydrolysis in a predominantly aqueous medium (r = 100), resulting in precipitated crystalline powders exhibiting brookite and anatase, which begin to transform to rutile below 500 C. Powders precipitated in a predominantly organic medium (r = 6) underwent partial hydrolysis, were highly porous and exhibited an amorphous structure, with crystallisation of anatase occurring at 300 C and transformation to rutile beginning at 500 to 600C.

This paper reports defect diagrams of Sr-doped lanthanum cobaltate, La1−xSrxCoO3−δ (LSC), involving both random defect model and the cluster defect model in the temperature range between 873 K and 1173 K. The diagrams are derived in the form of defects concentrations as a function of oxygen partial pressure using the nonstoichiometry data reported in the literature. The effect of the Sr content on defect structure of LSC is discussed in terms of both defect models.

This paper considers electrical properties of La1−xSrxCoO3−δ in terms of defect models, such as random defect model and the cluster model. It is shown that the experimental data of the electrical conductivity may be explained in terms of the random defect model rather than the cluster model.

This paper considers defect chemistry models of La1−xSrxCoO3−δ, such as random defect model and the cluster defect model. These models are considered in terms of defect equilibria with respect to (i) the formation of oxygen vacancies, (ii) intrinsic electronic ionisation and (iii) the formation of defect clusters. The defect models are derived using the available data of nonstoichiometry for the LSC materials.

This paper reports the results of work function and EPR studies of yttria-stabilized zirconia (10Y-ZrO2). The experimental data are considered in terms of the formation of oxygen chemisorbed species and subsequent oxygen incorporation as well as related charge transfer. It is concluded that oxygen chemisorption on 10Y-ZrO2 at room temperature in its initial stage results in the formation of O 2 − species. These species are then transformed into O 2 2− , O− species and, finally, are slowly incorporated into the oxide lattice. These processes take place without presence of Pt or any other electrode material.

This paper reports the results of the electrical conductivity measurements for polycrystalline specimens of undoped and Cr-doped CoO in the ranges of p(O2) (10−5 – 105 Pa) and temperature (1223 – 1373 K). The experimental data are considered in terms of the effect of Cr on semiconducting properties of CoO. It is shown that Cr results in a decrease of the reciprocal of the p(O2) exponent of electrical conductivity, however, the obtained experimental values are substantially lower than those predicted by defect chemistry. The activation energy of the electrical conductivity remains independent of p(O2) and Cr content (at the level of about 0.5 eV) except strongly reduced CoO, at p(O2)=2.10−4 Pa, of which the activation energy is substantially higher. Thermopowervs p(O2) exhibits maximum at p(O2)=10 Pa (except of thermopower data for Cr-doped CoO at the highest temperature). The experimental data are considered in terms of the effect of both p(O2) and Cr on semiconducting properties.

This paper concerns verification of the defect chemistry models of La1−xSrxCoO3−δ (LSC), involving the random defect model and the cluster defect model, against empirical data of oxygen nonstoichiometry. It appears that the experimental data may well be explained within the random defect model.

This paper reports application of the work function (WF) measurements for surface monitoring of perovskite-type electrode materials, such as (La,Sr)MnO 3 , (La,Sr)CoO 3 , (La,Sr)FeO 3 as well as Co-doped and Fe-doped (La,Sr)MnO 3 , during oxidation and reduction. The WF changes during oxidation at 1073 K are considered in terms of several processes of different rate of appearance, such as (a) oxygen chemisorption, (b) oxygen incorporation into the oxide lattice and related changes of Fermi energy, (c) non-stoichiometry-induced transient oxygen chemisorption (desorption), and (d) structural changes within the surface layer that are induced by changes in oxygen partial pressure.

A model describing the relationship between nonstoichiometry and Fermi energy was used to determine the effect of oxygen partial pressure on semiconducting properties of perovskite-type oxide materials, such as (La,Sr)MnO 3 . Specifically, this model was used to determine the electrical effects at the gas/solid interface for the oxygen/metal oxide system with specific respect to oxygen non-stoichiometry and oxygen chemisorption. It was found that oxidation of (La 0.8 Sr 0.2 )MnO 3 at both 1023 and 1073 K, corresponding to changes of p (O 2 ) in the range 10 and 21 kPa, results in the formation of a chemisorption-related surface potential barriers that assumes 0.165 V while oxidation at 1123 K leads to oxygen incorporation without changes in chemisorption equilibrium.

A model describing the effect of oxygen partial pressure on non-stoichiometry, in both cation and oxygen sublattices of oxide perovskite-type materials, such as (La,Sr)MnO 3 , and related changes in Fermi energy level, is derived. This model may be applied for evaluation of semiconducting properties of these materials from data of the deviation from stoichiometry.

The diffusion coefficient of Nb in BaTiO3 single crystal was determined from the Nb diffusion profile in the temperature range 1530–1723 K in air. The Arrhenius plot of the obtained diffusion data indicates that there is a change in the diffusion mechanism at 1626 K. At 1530 K these data are consistent with the chemical diffusion coefficient of Nb-doped BaTiO3. It was found that the transport in Nb at 1530 K and above this temperature occurs according to a different mechanism. Below 1481 K the process of Nb incorporation into BaTiO3 is substantially retarded.

This paper reports the results of the electrical conductivity measurements for Nb-doped BaTiO3 ceramics in the temperature range 1073–1373 K in both oxidizing and reducive atmospheres. The electrical conductivity was also applied to monitor the formation of Nb-doped BaTiO3. It is shown that the solid state reaction for the system BaTiO3–Nb2O3 takes place at 1573 K, but annealing at 1623 K is required to produce specimen of reproducible electrical properties. The solubility limit of Nb in stoichiometric BaTiO3 (Ba/Ti=1) at 1573 K in air is 5 at%. The p(O2) exponent of the electrical conductivity was determined (1/nσ=−1/3.9). This exponent is consistent with the defect disorder model of Nb-doped BaTiO3 derived assuming that ionic charge compensation prevails. The activation energy of the electrical conductivity for Nb-doped BaTiO3 depends on both p(O2) and Nb content.

This paper describes the application of a manometric method for the determination of the chemical diffusion coefficient for the electrode material (La 0.8 Sr 0.2 )MnO 3 in the temperature range 500–850°C. In the manometric method, the progress of a chemical reaction, such as oxygen incorporation into a non-stoichiometric oxide, can be monitored by the determination of changes in oxygen partial pressure. It was observed that the diffusion data obtained for oxidation and reduction differ essentially in both absolute values and their temperature dependence.

An industrial frit formulated in the new CaO–ZrO2–SiO2 glass–ceramic system was studied as a matrix for whisker reinforced composites. The frit was ball milled in acetone and wet ultrasonically mixed with 5, 10, 20, and 30 vol.-% SiC whiskers in order to overcome whisker agglomeration and obtain intimate mixing of the two phases. The samples were hot pressed at 14 MPa in graphite dies, using a N2 atmosphere, for 2 h at 1280°C. In order to investigate the effect of whiskers as a reinforcement, flexural strength as well as crack configuration and propagation were taken into consideration. Whisker orientation perpendicular to the hot pressing direction was found by SEM observation, and no carbon layer at the whisker/matrix interface was detected by EPMA. Further characterisation of the specimens involved physical (density, elastic modulus) and microstructural properties (XRD, SEM, TEM). The result of glass devitrification was inter locked wollastonite crystals.

The defect structure and morphology of h-GaN film grown by means of MOCVD on (0001) sapphire substrate has been studied by focused ion beam milling (FIB), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). Two different types of grain boundary defects having an anisotropic distribution are observed. For the first type, the grain boundaries surround the pyramid-shaped grains. These defects originate from the mismatch of the crystal lattices between the GaN film and the sapphire substrate. The grain boundary defects penetrate the GaN epilayer and the average grain size increases with increasing layer thickness up to about 500 nm from the interface to the top surface of the GaN film. For the second type, the grain boundaries surround the voids forming produced by impurities in the film. Both types of grain boundaries have a distribution with a hexagonal symmetry that may be the origin of the anisotropic transport properties observed previously in the GaN films.

The present work reports isothermal changes of oxygen non-stoichiometry for the perovskite-type electrode material (La0.8Sr0.2)MnO3 in the temperature range 945–1255 K. A thermogravimetric method was used to monitor the rate of the gas/solid equilibration. For equilibration degrees larger than 0.5, the equilibration kinetic data can be described by a diffusion equation. The determined chemical diffusion coefficient depends essentially on the oxygen partial pressure. Its temperature dependence can be expressed by the following expressions at low and high p(O2), respectively: $$D_{chem} = (1.9 \pm 1.6)10^{ - 3} {\text{exp}}\frac{{{\text{ - }}\left( {{\text{83}}{\text{.4}} \pm {\text{15}}{\text{.8}}} \right){\text{kJ mol}}^{{\text{ - 1}}} }}{{RT}}({\text{cm}}^{\text{2}} {\text{s}}^{{\text{ - 1}}} ){\text{ (1)}}$$ $$D_{chem} = (1.6 \pm 0.6)10^{ - 1} {\text{exp}}\frac{{{\text{ - }}\left( {{\text{121}}{\text{.2}} \pm 8.2} \right){\text{kJ mol}}^{{\text{ - 1}}} }}{{RT}}({\text{cm}}^{\text{2}} {\text{s}}^{{\text{ - 1}}} ){\text{ (2)}}$$

The present work reports equilibration kinetics for (La0.8,Sr0.2)CoO3(LSC) and (La0.72,Sr0.18)FeO3(LSF) in the temperature range 876–1114 K using a gravimetric method. Chemical diffusion determined in this way that depends on oxygen partial pressure, can be expressed by the following temperature dependence at low and high O2), respectively, for LSC: $$D_{chem} = 8.7 \times 10^{ - 3} {\text{exp}}\frac{{{\text{ - }}\left( {58.1 \pm 8.5} \right){\text{kJ/mol}}}}{{RT}}({\text{cm}}^{\text{2}} {\text{s}}^{{\text{ - 1}}} ){\text{ (1)}}$$ $$D_{chem} = 6.2 \times 10^{ - 3} {\text{exp}}\frac{{{\text{ - }}\left( {75.4 \pm 6.5} \right){\text{kJ/mol}}}}{{RT}}({\text{cm}}^{\text{2}} {\text{s}}^{{\text{ - 1}}} ){\text{ (2)}}$$ and for LSF: $$D_{chem} = 3.05 \times 10^{ - 5} {\text{exp}}\frac{{{\text{ - }}\left( {30.3 \pm 2.8} \right){\text{kJ/mol}}}}{{RT}}({\text{cm}}^{\text{2}} {\text{s}}^{{\text{ - 1}}} ){\text{ (3)}}$$ $$D_{chem} = 6.3 \times 10^{ - 3} {\text{exp}}\frac{{{\text{ - }}\left( {82.7 \pm 10.2} \right){\text{kJ/mol}}}}{{RT}}({\text{cm}}^{\text{2}} {\text{s}}^{{\text{ - 1}}} ){\text{ (4)}}$$

This paper overviews the present state of understanding on properties of the electrode material LiCoO2 as well as the impact of these properties on the electrode performance in lithium batteries. The properties that are important for applications, such as structure, non-stoichiometry, defect chemistry and related electrical properties are considered.

Fe-substituted Bi 2 Sr 2 Ca(Cu 1− y Fe y ) 2 O x single crystals have been studied by X-ray photoelectron spectroscopy (XPS) to determine the changes of oxidation states of their constitutes as well as the electronic structure of the valence band of the system. The core level lines of Bi exhibit two main components, which indicates either inequivalent sites or the presence of different oxidation states. The second component shows a systematic increase with Fe-substitution. The Sr lines also exhibit two components in which the lower binding energy component decreases with the dopant content. No significant changes in CuO 2 bilayers and Ca–O layer were observed. The results suggest a dramatic charge transfer between the Bi–O and Sr–O layers which compensates the increase of positive charge near the CuO 2 planes induced by Fe-substitution for Cu, and the impurity scattering of the dopants in the conduction band is one of the key factors for the T c suppression.

Metal-sheathed high-Tc superconducting current leads of Jc=1.6–1.8×104 A cm−2 at 77 K under self-field condition were fabricated using a modified short tape processing technique. It was found that section-wise uniaxial pressing can be used to provide the necessary intermediate mechanical deformation between heat treatments of long silver-sheathed (Bi,Pb)2Sr2Ca2Cu3O10+x superconductor. The overlapping of pressing up to 400 MPa does not impose non-uniformity of transport Jc to the final product. By stacking of single-core tapes, multi-layer current leads can be made. The Ic of this multi-layer current lead is additive, as in normal current in parallel-connected circuits. There is a lateral variation of Jc in the superconducting core of these leads.

Diffusion profiles of Ca in highly densified polycrystalline yttria-stabilized (10 mol %) ZrO 2 were investigated by secondary ion mass spectroscopy (SIMS). Lattice diffusion coefficient in temperature range of 1073 to 1273 K was determined: D Lattice =0.458 exp[−393.3 (kJ/mol)/ RT ] (cm 2 /sec). Grain boundary diffusion was estimated based on the Whipple's analysis. As a result, values of D Boundary δ s can be represented by D Boundary δ s =4.85×10 −13 exp[−185.8 (kJ/mol)/ RT ] (cm 3 /sec), where D Boundary is the grain boundary diffusion coefficient, δ the grain boundary width and s the segregation factor.

Work function (WF) of undoped and Gd-doped PbZrO3 (PZG) was determined during isothermal oxidation and reduction experiments at 400 and 500 °C in the P(O2) range between 10 and 2.1×104 Pa. The obtained results are discussed in terms of two competitive effects, such as (i) an acceptor-type effect due to oxygen chemisorption and its subsequent incorporation into the oxide lattice and (ii) donor-type effect due to p(O2)-induced structural transitions, such as decomposition of PbZrO3 resulting in the formation of a surface layer composed of PbO and ZrO2. Both effects have different rates of appearence and the effect on electrical potential. It was found that oxidation results in irreproducible changes of surface properties involving the formation of a low-dimensional surface layer.

This paper reports the results of work function (WF) changes of undoped PbZrO3 during subsequent isothermal oxidation and reduction experiments at 500°C in the p(O2) range between 10 and 2.1 × 104 Pa. The results, obtained during three consecutive runs, indicate that heating at 500°C leads to continuous changes of surface properties resulting in a complex WF vs. time characteristic. The WF changes during the first oxidation are determined by a p(O2)-induced structural transition. The second oxidation results in two competitive processes, such as rapid increase of oxygen non-stoichiometry followed by a structural transition. Finally, the third oxidation is determined by changes of oxygen nonstoichiometry.

This paper reports surface electrical properties of zirconia studied using work function measurements in the temperature range 297–1173 K during oxidation. It was found that surface preparation procedures, such as grinding and polishing, result in a change of its reactivity with oxygen. The effects produced by the preparation can be removed during thermal treatment at 1473 K.

The surface vs. bulk defect chemistry of zirconia is considered in terms of electrical properties, such as electrical conductivity (bulk) and work function (surface). The difference between the two is considered in terms of segregation-induced concentration gradients. It is postulated that the transport of charged defects through the interface layer of zirconia may be influenced strongly by the local electric field, which is formed within this layer across the segregation-induced concentration gradients. The effect of this field on the oxidation kinetics of metals and alloys, such as Zircaloy, is considered.

The equilibration kinetics of single-crystal TiO2 were determined in the rapid kinetics regime (within the first 10 h) within narrow ranges of oxygen activities, p(O2), under the conditions of 1198–1323 K and p(O2) = 10–10–105 Pa. The determined chemical diffusion coefficient, Dchem, is observed to exhibit a complex dependence on p(O2). Comparison of Dchem for single-crystal and polycrystalline TiO2 demonstrates that the grain boundaries have a retarding effect on the transport of defects. The present work represents the first assessment of the effect of nonstoichiometry on well defined Dchem for TiO2 within a wide range of p(O2). (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The semiconducting properties of single-crystal TiO2 and their changes during prolonged oxidation at elevated temperatures and under controlled oxygen activity were monitored using measurements of electrical conductivity and thermo-electric power. Two kinetic regimes were revealed: Regime I – rapid oxidation, associated with the transport of oxygen vacancies, and Regime II – prolonged oxidation, which corresponds to the transport of titanium vacancies. The present data represent the first documented evidence for the formation and transport of titanium vacancies in TiO2. This finding allows the processing of p-type TiO2 without the incorporation of aliovalent foreign ions. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The present study, reported in a series of eleven papers summarised here, has aimed to determine the mechanism and kinetics of reactivity between zirconia and oxygen at elevated temperatures. The study is based on in situ monitoring of work function changes during oxidation and reduction of yttria-stabilised zirconia (YSZ). The reactivity of YSZ with oxygen was determined in terms of both oxygen chemisorption and oxygen incorporation and related charge transfer. The obtained work function data have been used to determine the oxygen chemisorption isobar for YSZ. The effect of surface properties on the reactivity of YSZ with oxygen has been assessed and the application of surface processing for the modification of reactivity examined. It has been found that work function measurements may be used for in situ examination of surface properties of oxide materials during processing at elevated temperatures and in gas phases of controlled composition.

A modified melt-textured-growth (MTG) method which has a relatively low working temperature and short reaction time compared with the conventional MTG method has been developed. The number of YBa 2 Cu 3 O 7− y (123) nuclei during the initial slow-cooling process has been minimized which leads to the enhancement of the 123 grain growth rate and a better homogenized and smaller Y 2 BaCuO 5 (211) particles over the samples. Magnetization measurement shows that the 123 crystals have a high J c and a good performance in high magnetic fields.

The influence of mechanical strain on the critical current density J c (77 K) of single- and multi-filament silver-sheathed Bi(Pb)2223 (Bi 2− x Pb x Sr 2 Ca 2 Cu 3 O 10− y ) superconducting tapes was investigated by cyclic double-bend tests. The irreversible strain limits ϵ irr determined were compared with those measured using single-bend tests. It was found that the decrease in the J c is determined primarily by the bending radius while cyclic stress caused further deterioration. However, a large percentage of the J c is retained at large strain (⪢ ϵ irr ) and through repeated bending. Scanning electron microscopy revealed that the deterioration resulted from microstructural damage in the form of cracks. At strains just beyond the irreversible strain limit, cracks developed only on the sides of the samples subjected to tensile strains. At large strains, cracks also were found on the compressive sides. The magnetic field dependence of the J c was measured on samples subjected to various strain levels. The results suggest that the effect of strain on the J c is extrinsic and that microstructural damage is the only cause of the deterioration.

Functionally gradient materials (FGM), a recent development in composite materials, consist of a continuously graded interface between two component phases. Previously reported FGM fabrication methods are reviewed, including vapour deposition, plasma spraying, electrophoretic deposition, controlled powder mixing, slipcasting, sedimentation forming, centrifugal forming, laser cladding, metal infiltration, controlled volatilization, and self propagating high-temperature synthesis. A novel approach to FGM fabrication is presented involving thixotropic casting — vibratory casting of highly concentrated highly thixotropic suspensions castable only under vibration. The hydroxyapatite/316L stainless steel system (a biocompatible ceramic/metal system) was used due to appropriate matches in true densities, thermal expansion, and sintering temperatures. Solids loadings from 76.08–82.67 wt% were trialled. Solids loading was found to be critical. At 78.17 wt%, an ideal continuous FGM formed, showing a gradual transition from pure ceramic to pure metal across 60 mm. At the nearest increments trialled (±0.3 wt%) gradation was far from optimal: 77.87 wt% gave a sharp ceramic/metal interface with negligible grading; 78.47 wt% gave a relatively homogeneous sample with only a small degree of grading, from a slightly metal-rich end to a slightly metal-poor end.

The effects of contact area as well as the weight fraction of Y 2 BaCuO 5 (211) substrate on the melt textured growth (MTG) of YBa 2 Cu 3 O 7-δ (123) crystals are investigated. It is found that the 123 grain size and its orientation have been greatly improved by a well designed 211 substrate with maximized number of contact points. The size of the 123 single domain has been extended up to 2.7 cm with no porosity and cracks by applying 50% of contact area and 35% of absorbed liquid weight into 211 substrate. Magnetization and levitation measurements show that the MTG 123 crystals have a high J c and a good performance in high magnetic fields.

Sr-based 123 compounds R 1-x Ca x Sr 2 Cu 2.7 Mo 0.3 O y with R = Pr, Nd, and Y are successfully stabilised by partial substitution of Mo for Cu. A tetragonal-orthorhomic-tetragonal transition is observed for R = Y and Nd, which is induced by different oxygen content in the samples. T c of the samples is sensitive to the oxygen content other than the structure. For Pr-contained samples the resistivity decreases systematically with increasing the Ca dopant and oxygen content. The results show that the hybridisation of the conduction electrons with the 4f band of Pr in Sr-based 123 compounds is weaker than that in Ba-based 123 compounds.

The scaling behaviour of I - V characteristics has been studied in melt-textured YBa 2 Cu 3 O 7− y samples with and without weak links, at different temperatures and magnetic fields. The I - V curves are found to obey the scaling behaviour of the vortex-glass transition, but the transition temperature and the scaling exponent are different for these two kinds of samples. The results have been explained with vortex-glass transition in intergranular and intragranular regions.

The scaling behaviour of vortex-glass superconductivity is studied, by measuring the resistive transition as well as the I - V curve under a variety of magnetic fields, in a series of V doped YBa 2 Cu 3 O 7− y samples with different grain sizes. The equilibrium phase boundary line between the normal and superconducting phases in the H - T plane obtained by fitting the resistive transition is consistent with that obtained by the I - V curve measurements. As the magnetic field is lower than a certain value, H s , the scaling exponents are magnetic-field independent, but at H = H s , they begin to increase with the magnetic field and gradually get saturation. The switch field, H s , decreases with decreasing the grain size in the samples. The results show that the magnetic-field-dependent scaling behaviour of the I - V curve observed in weak-link containing systems originates from the transition of a “weak” vortex-glass state to a “strong” vortex-glass state.

Highly regular dislocation networks in the high- T c (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O 10+ x phase in mechanically deformed, multifilamentary, Ag sheathed, superconducting tapes have been observed by means of transmission electron microscopy. The dislocation density in the network region was calculated to be 1.0 × 10 10 cm −2 . Using these observations in conjunction with uniaxial tensile tests of the superconducting tapes and pure annealed silver, the Young modulus and the stacking-fault energy on the basal plane in this phase were estimated to be 2.55 GPa and 10.5 mJ m −2 , respectively. The implications of the low stacking-fault energy on the basal plane are discussed.

Ab-initio density functional theory (DFT) calculations of the relative stability of anatase and rutile polymorphs of TiO2 were carried using all-electron atomic orbitals methods with local density approximation (LDA). The rutile phase exhibited a moderate margin of stability of ~ 3 meV relative to the anatase phase in pristine material. From computational analysis of the formation energies of Si, Al, Fe and F dopants of various charge states across different Fermi level energies in anatase and in rutile, it was found that the cationic dopants are most stable in Ti substitutional lattice positions while formation energy is minimised for F- doping in interstitial positions. All dopants were found to considerably stabilise anatase relative to the rutile phase, suggesting the anatase to rutile phase transformation is inhibited in such systems with the dopants ranked F>Si>Fe>Al in order of anatase stabilisation strength. Al and Fe dopants were found to act as shallow acceptors with charge compensation achieved through the formation of mobile carriers rather than the formation of anion vacancies.

The agglomeration, electrokinetic properties and electrophoretic deposition behaviour of aqueous suspensions of ZrO2 with carboxylic acid additives were studied in comparison with conventional pH adjustment. It was found that citric acid imparted negative zeta-potential values and electrosteric stabilisation to particles in suspensions at all pH levels. The examination of additions of carboxylic acids to ZrO2 suspensions revealed that these reagents cause a sharp drop in zeta-potential at distinct addition levels, which correspond to surface saturation of the particles with negatively charged carboxylate groups. Adsorption cross sections of citric acid, EDTA and oxalic acid were evaluated from these results, showing that both citric acid and EDTA coordinate to ZrO2 surfaces by two carboxylate groups while oxalic acid is coordinated by one group. The use of carboxylic acids was shown to facilitate superior electrophoretic deposition in comparison with zeta-potential modification by conventional pH adjustment through improved suspension stability.

Ceramic matrix composites (CMCs) are preferred to their monolithic ceramics particularly in high temperature applications. In CMCs, enhanced toughening is obtained through mechanisms such as crack-deflection, whisker/fiber pull-out, debonding, crack pinning and micro-cracking. In a recent paper, the authors presented preliminary results of a study of mechanical and fracture property of an Al[sub 2]O[sub 3]/SiC [sub whisker] CMC at high temperatures. Additional work has been carried out with this material as well as with a Si[sub 3]N[sub 4]/SiC[sub whisker] CMC. This paper presents the comparative performance, ie., mechanical and fracture properties of these two CMCs tested at 1,100 C and 1,200 C in an argon atmosphere.