Jonathan S. Morrell

Sol-Gel Synthesis of Rare Earth Aluminate Films as Buffer Layers for High Tc Superconducting Films

Cubic rare-earth aluminate perovskites of the general form REAIO 3 have been identified as possible buffer layers for high current carrying cuprate superconductors deposited on roll-textured metals. This paper describes on-going research to develop solution routes which would avoid the use of slow and costly vacuum processing. Our research plan includes the development of an appropriate solution chemistry, studies of the crystallization behavior of powders under reducing and oxidizing conditions, deposition of polycrystalline films on silver substrates, deposition of epitaxial films on single-crystal oxide substrates, and deposition on roll textured nickel. The method is illustrated with the example of PrAlO 3 .

Epitaxial growth of gadolinium oxide on roll-textured nickel using a solution growth technique

Chemical solution epitaxy was used to deposit an epitaxial film of Gd 2 O 3 on roll-textured nickel. A 2-methoxyethanol solution of gadolinium methoxyethoxide was used for spin-coating and dip-coating. Films were crystallized using a heat treatment at 1160 °C for 1 h in 4% H 2 /96% Ar. Single-layer films were approximately 600 A in thickness, and thicker films could be produced using multiple coatings. θ/2θ x-ray diffractograms revealed only (0041) reflections, indicating a high degree of out-of-plane texture. A pole-figure about the Gd 2 O 3 (222) reflection indicated a single in-plane epitaxy. Scanning electron microscopy showed that the films were smooth, continuous, and free of pin holes. Atomic force microscopy revealed an average surface roughness of 53 A. Electron diffraction indicated that the misalignment of the majority of the grains in the plane was less than 10°. High-current (0.4 MA/cm 2 ) Yba 2 Cu 3 O 7–δ films were grown on roll-textured nickel substrates using Gd 2 O 3 as the base layer in a three-layer buffer structure.

Microstructure of a high Jc, laser-ablated YBa2Cu3O7−δ/sol–gel deposited NdGaO3 buffer layer/(001) SrTiO3 multi-layer structure

Abstract A YBa 2 Cu 3 O 7− δ (YBCO) film with a transport critical current density ( J c ) value of 1 mA/cm 2 (77 K, 0 T) was grown on a solution deposited NdGaO 3 (NGO) buffer layer on (100) SrTiO 3 (STO). The 25-nm thick NGO buffer layer was dip-coated onto the STO single crystal from a solution of metal methoxyethoxides in 2-methoxyethanol. Pulsed laser deposition (PLD) was used to grow a 250-nm-thick YBCO film on the NGO. The epitaxial relationships are cube-on-cube throughout the structure when the pseudo cubic and pseudo tetragonal unit cells are used to describe the NGO and YBCO crystal structures, respectively: (001) YBCO∥(001) NGO∥(001) STO and [100] YBCO∥[100] NGO∥[100] STO. High resolution scanning electron microscopy (SEM) of the bare NGO surface revealed ∼40 nm diameter pinholes with number density of ∼2×10 13 m −2 , corresponding to an area fraction coverage of 2.5%, in an otherwise featureless surface. Cross-sectional transmission electron microscopy (TEM) showed that these pinholes penetrate to the STO; otherwise the NGO layer was uniformly thick to within approximately ±5 nm and defect free. The X-ray diffraction φ- and ω-scans indicated that the YBCO film was highly oriented with a full-width-half maximum peak breadth of 1.14° for in-plane and 0.46° for out-of-plane alignment, respectively. The film contained sparse a -axis oriented grains, an appreciable density of (001) stacking faults and apparently insulating second phase precipitates of the type that typically litter the surface of PLD films. All of these defects are typical of YBCO thin films. High-resolution cross-sectional TEM images indicate that no chemical reaction occurs at the YBCO/NGO interface.

Machining with nanomaterials

Fundamentals of Machining.- Machining Stability.- Machining Chatter Suppression.- Micromachining from a Materials Perspective.- Machining Brittle Materials Using Nanostructured Diamond Tools.- Analysis of Contact Between Chip and Tool Using Nanostructured Coated Cutting Tools.- Economic Analysis of Machining Using Nanostructured Coated Cutting Tools.- Analysis of Machining Hardened Steels Using Coated Cutting Tools.- Formation of Nanostructured Metals.- Manufacture and Development of Nanostructured Diamond Tool.

Fundamentals of Machining

During chip formation there is a substantial increase in the specific energy as chip size is reduced during machining. It is believed this is due to the fact that all metals contain defects such as grain boundaries, missing and impurity atoms, and when the size of the material removed decreases the probability of encountering a stress-reducing defect decreases. Since the shear stress and strain in metal cutting is unusually high, discontinuous microcracks usually form on the primary shear plane. If the material is very brittle, or the compressive stress on the shear plane is relatively low, microcracks will grow into larger cracks giving rise to discontinuous chip formation. When discontinuous microcracks form on the shear plane they will weld and reform as strain proceeds, thus joining the transport of dislocations in accounting for the total slip of the shear plane. This chapter focuses on machining at the micro- and nanoscale and attempts to explain the dominant features of machining as the size effect becomes significant.

Residual surface stress: comparing traditional and modulated tool path machining processes

Traditional machining processes, where material is removed by a cutting tool from a workpiece, can introduce residual stresses at the surface of machined pieces. This paper provides an examination of an alternative machining methodology called modulated tool path machining. The ultimate objective of this research is to determine the effects of modulated tooling path machining processes, as applied to control chip geometry, on the surface stress of selected materials. Residual stresses in machined samples were characterised through the use of X-ray diffraction by comparing the modulated path method with a more traditional material removal technique (i.e. constant surface speed and constant contact). This paper is part of a Themed Issue on Measurement, modelling and mitigation of residual stress.

Solution synthesis of epitaxial films of bismuth containing ferroelectric materials

Abstract Methoxyethoxide complexes in 2-methoxyethanol were used to produce epitaxial thin films of SrBi2Nb2O9, SrBi2Ta2O9, BaBi2Nb2O9, and BaBi2Ta2O9 on [100] oriented single-crystals of SrTiO3 and LaAlO3. Films were prepared by spin coating substrates with alkoxide solutions and firing in air at 850 °C for 20 minutes. With the exception of BaBi2Ta2O9 on LaAlO3, all of the films were the desired c-axis oriented Aurivillius phase. Out-of-plane orientation was confirmed by θ-2θ scans which showed only [002/] reflections, and in-plane orientation was determined by phi-scans about the [105] plane. Lattice constants and full-width at half-maximum (fwhm) values for both in-plane and out-of-plane reflections are reported.

Synthesis of a potential semiconductor neutron detector crystal LiGa(Se/Te)2: materials purity and compatibility effects

Lithium containing AIBIIICVI semiconductors are being considered as alternative materials for room temperature neutron detection. One of the primary challenges in growing a high quality crystal of such a material is the reactivity of lithium metal. The presence of nitrides, oxides, and a variety of alkali and alkaline earth metal impurities prevent pure synthesis and truncate crystal growth by introducing multiple nucleation centers during growth. Multiple lithium metal purification methods have been investigated which ultimately raised the metal purity to 99.996%. Multi-cycle vacuum distillation removed all but 40 ppm of metal impurities in lithium metal. LiGa(Se/Te)2 was then synthesized with the high purity lithium metal by a variety of conditions. Lithium metal reacts violently with many standard crucible materials, and thermodynamic studies were undertaken to insure that an appropriate crucible choice was made, with high purity iron and boron nitride crucibles being the least reactive practical materials. Once conditions were optimized for synthesis of the chalcopyrite, vertical Bridgman crystal growth resulted in red crystals. The optical, electronic, and thermodynamic properties were collected.

Computational analysis of the intimate contact between an inclined wedge and low carbon steel during metal cutting

The initial stages of intimate contact between an inclined wedge and low carbon steel creates significant opportunities for manufacturers of machined products to understand how dry machining and minimum quantity lubrication affect the economics of manufacturing, especially when one considers how important frictional interactions between chip and tool are on the final structure of the workpiece materials in terms of structural phase transformations. The present work not only compares various computational approaches to the solution of shear plane and tool face temperatures, but also explains why there is a large discrepancy when calculating temperature generated during machining when using Loewen and Shaws method for calculating shear plane and tool face temperatures.

Micromachining from a Materials Perspective

Mechanical micromachining is a technique that has the potential to become a successful small-scale manufacturing process. If the abilities of macromachining can be scaled down to the microscale, then a versatile manufacturing technique will be created that is capable of processing a wide variety of materials. However, simply scaling down machines is not the solution, reducing the scale from macro to micro presents unique problems that must be overcome that include eliminating tool wear, machining heterogeneous workpiece materials in a uniform manner, and advances in machine tool design. Therefore, a review of the aspects of machining is presented that focuses on the machining process from a materials perspective.