The growth, structure and properties of sputtered barium titanate thin films

The design and construction of a sputtering system for the deposition of barium titanate thin films is described. The growth and structure of barium titanate films deposited on a variety of substrates including amorphous carbon fi1ms, potassium bromide single crystals, and polycrystalline gold films has been studied. Films deposited on all substrates at room temperature were amorphous. Polycrystalline titanate films were formed on polycrystalline and amorphous substrates at temperatures above 450°C while films with a pronounced texture could be expitaxially deposited on single crystal potassium bromide above a temperature of only 200°C. Results of dielectric measurements made on the films are reported. Amorphous films were highly insulating (resistivities ~1014 ohm.cm with dielectric constants of between 10 and 20.

Precipitation studies on alloys from the system copper chromium zirconium

The precipitation reactions occurring in a series of copper-based alloys selected from the system copper-chromium-zirconium have been studied by resistometric and metallographic techniques. A survey of the factors influencing the development of copper-based alloys for high strength, high conductivity applications is followed by a more general review of contemporary materials, and illustrates that the most promising alloys are those containing chromium and zirconium. The few systematic attempts to study alloys from this system have been collated, discussed, and used as a basis for the selection of four alloy compositions viz:- Cu - 0.4% Cr Cu - 0.24. Zr Cu - 0. 3% Cr - 0.1% Zr Cu - 0.2% Cr - 0.2% Zr A description of the experimental techniques used to study the precipitation behaviour of these materials is preceeded by a discussion of the currently accepted theories relating to precipitate nucleation and growth. The experimental results are presented and discussed for each of the alloys independently, and are then treated jointly to obtain an overall assessment of the way in which the precipitation kinetics, metallography and mechanical properties vary with alloy composition and heat treatment. The metastable solid solution of copper-chromium is found to decompose by the rejection of chromium particles which maintain a coherent interface and a Kurdjumov-Sachs type crystallographic orientation relationship with the copper matrix. The addition of 0.1% zirconium to the alloy retards the rate of transformation by a factor of ten and modifies the dispersion characteristics of the precipitate without markedly altering the morphology. Further additions of zirconium lead to the growth of stacking faults during ageing, which provide favourable nucleation sites for the chromium precipitate. The partial dislocations bounding such stacking faults are also found to provide mobile heterogeneous nucleation sources for the precipitation reactions occurring in copper-zirconium.

An investigation into the depandance of electrical properties on microstructure in polycrystalline barium titanate

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Highly selective Pd/titanate nanotube catalysts for the double-bond migration reaction

Pd(II) and Pd(0) catalysts supported onto titanate nanotubes (H2Ti3O7) were prepared by an ion-exchange technique. The catalysts are characterised by narrow size distribution of metal nanoparticles on the external surface of the nanotubes. Pd(II) catalysts show high selectivity toward double-bond migration reaction versus hydrogenation in linear olefins. The catalytic activity exhibits a volcano-type dependence on the metal loading, with the maximum activity observed at ca. 8 wt%. The Pd(II) was shown to be rapidly reduced to Pd(0) by appropriate choice of solvent. Prereduced Pd(0) catalysts were found to be less active toward double-bond migration and more selective toward hydrogenation. The DBM reaction was faster in protic solvents, such as methanol or ethanol. © 2006 Elsevier Inc. All rights reserved.

Zirconium phosphate supported tungsten oxide solid acid catalysts for the esterification of palmitic acid

A series of zirconium phosphate supported WOx solid acid catalysts with W loadings from 1–25 wt% have been prepared on high surface area zirconium phosphate by a surface grafting method. Catalysts were characterized by N2 adsorption, FTIR, Raman, UV-Vis, 31P MAS NMR, pyridine TPD and X-ray methods. Spectroscopic measurements suggest a Keggin-type structure forms on the surface of zirconium phosphate as a ([triple bond, length as m-dash]ZrOH2+)(ZrPW11O405−) species. All catalysts show high activity in palmitic acid esterification with methanol. These materials can be readily separated from the reaction system for re-use, and are resistant to leaching of the active heteropolyacid, suggesting potential industrial applications in biodiesel synthesis. © The Royal Society of Chemistry 2006.

Heavy ion irradiation effects in zirconium nitride

Polycrystalline zirconium nitride (ZrN) samples were irradiated with He +, Kr ++, and Xe ++ ions to high (>1·10 16 ions/cm 2) fluences at ∼100 K. Following ion irradiation, transmission electron microscopy (TEM) and grazing incidence X-ray diffraction (GIXRD) were used to analyze the microstructure and crystal structure of the post-irradiated material. For ion doses equivalent to approximately 200 displacements per atom (dpa), ZrN was found to resist any amorphization transformation, based on TEM observations. At very high displacement damage doses, GIXRD measurements revealed tetragonal splitting of some of the diffraction maxima (maxima which are associated with cubic ZrN prior to irradiation). In addition to TEM and GIXRD, mechanical property changes were characterized using nanoindentation. Nanoindentation revealed no change in elastic modulus of ZrN with increasing ion dose, while the hardness of the irradiated ZrN was found to increase significantly with ion dose. Finally, He + ion implanted ZrN samples were annealed to examine He gas retention properties of ZrN as a function of annealing temperature. He gas release was measured using a residual gas analysis (RGA) spectrometer. RGA measurements were performed on He-implanted ZrN samples and on ZrN samples that had also been irradiated with Xe ++ ions, in order to introduce high levels of displacive radiation damage into the matrix. He evolution studies revealed that ZrN samples with high levels of displacement damage due to Xe implantation, show a lower temperature threshold for He release than do pristine ZrN samples.

Unfolding grain size effects in barium titanate ferroelectric ceramics

Grain size effects on the physical properties of polycrystalline ferroelectrics have been extensively studied for decades; however there are still major controversies regarding the dependence of the piezoelectric and ferroelectric properties on the grain size. Dense BaTiO3 ceramics with different grain sizes were fabricated by either conventional sintering or spark plasma sintering using micro- and nano-sized powders. The results show that the grain size effect on the dielectric permittivity is nearly independent of the sintering method and starting powder used. A peak in the permittivity is observed in all the ceramics with a grain size near 1μm and can be attributed to a maximum domain wall density and mobility. The piezoelectric coefficient d33 and remnant polarization Pr show diverse grain size effects depending on the particle size of the starting powder and sintering temperature. This suggests that besides domain wall density, other factors such as back fields and point defects, which influence the domain wall mobility, could be responsible for the different grain size dependence observed in the dielectric and piezoelectric/ferroelectric properties. In cases where point defects are not the dominant contributor, the piezoelectric constant d33 and the remnant polarization Pr increase with increasing grain size.