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A high pressure SPS (spark plasma sintering) process was applied for consolidation of un-doped polycrystalline magnesium aluminate spinel. This approach allows fabricating a fully dense transparent ceramic with submicron grain size and high hardness values at a relatively low temperature (1200 °C). The light transmittance of the specimens increases with increasing applied pressure, while the hardness gradually decreases. The optimal combination of properties was achieved after sintering at 1200 °C at a heating rate of 5°/min, a holding time of 15 min and an applied pressure of 350–400 MPa. The specimens display the level of transmittance in the visible wavelengths and hardness values comparable with the best results reported in the literature for the two-stage fabrication process (pressureless sintering and hot isostatic pressing).

The present study deals with a comprehensive comparison of the mechanical and functional properties of Nd:YAG single crystals with those of the polycrystalline ceramics (PCs), undoped and LiF-doped, processed by Spark Plasma Sintering (SPS). The polycrystalline ceramics have higher mechanical properties (hardness, bending strength and thermal shock resistance) than the single crystals. The optical transmittance of the LiF-doped PC Nd:YAG is significantly higher than that of the undoped one and is close to that of the single crystal. With respect to other optical and thermal properties, i.e. refraction index, absorption coefficient, extinction ratio, thermo-optic coefficient, fluorescence and thermal conductivity, no significant differences were observed between the single crystals and the polycrystalline ceramic.

This work reports results of silicon carbide plates, disks, pipes, and pipe–disk couples bonded by a spark plasma sintering apparatus. The joining was conducted at 1900 °C for 30 min with a 35 MPa uniaxial pressure. The samples were analyzed by Scanning acoustic microscopy, which in turn revealed a low amount of small defects at the samples’ periphery. Scanning acoustic microscopy results were verified through scanning electron microscopy and nanoindentation. It was concluded that Spark Plasma Sintering technique may serve as a valid and effective tool for diffusion bonding of high-temperature-resistant silicon carbide with different geometries.

We show that the sensitivity and depth selectivity of neutron reflectometry can be greatly enhanced through a waveguide design that takes advantage of the spin-dependent magnetic neutron scattering potential to steer spin-up and spin-down neutrons into waveguide modes with different depth profiles. Using a bilayer of manganate and ruthenate ferromagnets, we demonstrate that a magnetic waveguide structure with sharp spin-up and spin-down modes centered in the two different layers can be generated by adding a magnetically inactive capping layer. The resulting reflectometric data allow accurate and reliable determination of a small in-plane magnetization in the ruthenate layer, despite its immediate proximity to the manganate layer with much larger magnetization. Magnetic neutron waveguides thus enable depth-sensitive measurements of small electronic spin polarizations in a large variety of magnetic multilayers and devices.

Ultra-low power turbine drives are used as energy sources in auxiliary power systems, energy units, terrestrial, marine, air and space transport within the confines of shaft power Ntd = 0.01...10 kW. They represent a set of input, output devices and an ultra-low power turbine (ULPT). The main objective of this article is to describe and to validate a new modified method for selecting rational parameters of two-stage axial ULPT with pressure stages that is based on the multi-objective optimization in conditions of initial data uncertainty. Using this method allows to design a high-performance turbine already at the preliminary design. This paper proposes an approach to the development of surrogate models for evaluating the integrated efficiency of two-stage ultra-low power turbine with pressure stages that is based on the use of existing mathematical models of turbine stage efficiency and mass. The paper describes the basic features of subroutine algorithm for parameters optimization and for efficiency criteria evaluating of a two-stage turbine. This method is intended for use at the preliminary design of a turbine drive. Results of optimization through this method can be applied at the stages of 3D gas-dynamic flow simulation, design and manufacturing of a turbine physical model. The method was tested at preliminary design of an air starter turbine for starting a diesel engine in cold climatic conditions. Validation of the method was carried out by comparing the results of optimization calculations and numerical gas-dynamic simulation in the Ansys CFX package. The results indicate a sufficient accuracy of the developed method for selection of two-stage turbine parameters.

Transparent Co 2+ doped MgAl 2 O b4 spinel was fabricated by SPS consolidation followed by and HIP treatment. It was established that HIP treatment significantly improved transparency of the ceramic in a wide range of wavelengths, especially, in a range, which is relevant for Q-switching. Nonlinear absorption was demonstrated and the ground and excited state absorption cross sections were estimated. The positive effect of the HIP treatment on the optical properties is related to an elimination of extremely fine porosity and to the location of Co ions at Mg 2+ sites in the spinel ionic structure. The experimental results indicate that the fabricated specimens can be used as a passive laser Q-switching material.

Al 2 O 3 –TiC composites were fabricated using spark plasma sintering (SPS) technology between 1300 °C and 1500 °C. The composite densification process starts at 950 °C, with a maximum densification rate at 1170 °C. After thirty minutes soaking at 1400 °C, a relative density of 99.5% was achieved. Microstructure analysis reveals a submicron Al 2 O 3 grain size and homogenous distribution of titanium carbide in the matrix. The fully dense Al 2 O 3 –20 wt% TiC composite exhibits high values of fracture toughness (8.3 MPa m 1/2 ), Young׳s modulus (406 GPa), flexural strength (850 MPa) and hardness (21 GPa).

International audience; Densification of cuboidal micrometer-sized lithium fluoride particles as ductile ceramic by spark plasma sintering (SPS) was investigated. Specimens were fabricated at different pressures and temperature conditions, ranging from 2 to 100 MPa at 500 °C and from 200 to 700 °C under 100 MPa of applied pressure, respectively. Dense specimens of 99 % relative density were fabricated by heating to 500 °C under constant pressure of 100 MPa. The densification showed first compaction by particle rearrangement, followed by plastic deformation via dislocation glide. Hot-pressing models were used to describe the densification by considering the temperature dependences of the yield stress, the strain hardening behavior and coefficients, and the pore size and shape dependences on the applied stress. A good agreement was found between the experimental and the theoretical densification curves. At low pressure of 2 MPa, the densification occurs by particle sliding, assisted by viscous flow at their surfaces, and local plastic deformation at the particle contacts, due to the intensified local stress. Finally, the micrometer-sized structural features and the contiguity achieved by plastic deformation at the start of spark plasma sintering (SPS) nullify any field effects in this model system at higher pressures; good agreement was obtained with expected conventional hot pressing.

A challenge in inertial fusion energy (IFE) research is to deliver the target to the target chamber center at a high repetition rate. Therefore, the problem of target fabrication and delivery is focused on methods that scale to highly repeatable and cost-effective target production. In this paper, we investigate the possibility of using magnetic-levitation (maglev) transport systems for noncontact manipulation, positioning, and delivery of the cryogenic targets. We focus on the development of transport systems based on movement of high-temperature superconductors (HTSC) over a permanent magnet guideway (PMG). Active guidance is achieved using the HTSC ceramics YBa2Cu3O7−X and PMG, where an ordered motion is initiated by a special arrangement of the permanent magnets. At present, significant R&D programs are ongoing in order to fulfill the technical requirements and basic elements of the system’s operation as a maglev target accelerator. We present here the main results of this work along with recent results.

Compressive creep properties of AlSi10Mg parts produced by additive manufacturing selective laser melting (AM-SLM) were studied using a spark plasma sintering (SPS) apparatus, capable of performing uniaxial compressive creep tests. Stress relief-treated specimens were tested under an applied stress of 100–130 MPa in the 175–225 °C temperature range. Utilizing two different configurations, the creep tests were conducted either with or without a low-density electric current (∼2.63–3.26 A/mm2) flowing through the test specimens. The results revealed that the creep rate increased under the influence of an applied electric current. The creep parameters (i.e., stress exponent n and apparent activation energy Q), were empirically determined. The stress exponent values were found to be 19.6 ± 1.2 and 16.2 ± 1.4 with and without current, respectively, while apparent activation energy was found to be 142 ± 9 kJ/mol and 150 ± 13 kJ/mol with and without current, respectively. The experimental results, together with microstructural examination of specimens, indicate that plastic deformation was controlled by dislocation activity. Furthermore, it is suggested that the annihilation process of dislocations during creep was enhanced by the electric current.

The strengthening of aluminum alloy 6061 (AA6061) by different point defects was determined experimentally using a shock wave technique. Decay of the amplitude of elastic precursor wave τ e l with propagation distance h was studied in four groups of AA6061 samples, namely, that in the super-saturated solid solution state (SSSS), and those strengthened by atomic clusters (short-range order), by Guinier-Preston zones I and by Guinier-Preston zones II after, respectively 7.5, 240 and 960 min aging of the SSSS samples at 145 °C. The dependences τ e l ( h ) were found to be kinked at stress τ * , corresponding to the transition of the control of dislocation motion from phonon viscous drag at τ e l > τ * to thermally activated obstacle passage at τ e l τ * . The values of strengthening by atomic clusters, GP-I, and GP-II zones were found equal to τ sro = 67 , τ GP - I = 67 , and τ GP - II = 124 MPa , respectively. Activation volumes corresponding to the interaction of dislocations with the studied defects, estimated based on τ e l τ * segments of the measured dependences τ e l ( h ) , were found to be in reasonable agreement with existing concepts of dislocation/defect interactions.

We carry out an experimental feasibility study of a magnetic field sensor based on the kinetic inductance of the high-$T_\mathrm{c}$ superconductor yttrium barium copper oxide. We pattern thin superconducting films into radio-frequency resonators that feature a magnetic field pick-up loop. At 77 K and for film thicknesses down to 75 nm, we observe the persistence of screening currents that modulate the loop kinetic inductance. According to the experimental results the device concept appears attractive for sensing applications in ambient magnetic field environments. We report on a device with a magnetic field sensitivity of 4 pT/Hz${}^{1/2}$, an instantaneous dynamic range of 11 $\mu$T, and operability in magnetic fields up to 28 $\mu$T., Comment: 12 pages, 12 figures

X-ray diffraction (XRD) and medium-energy ion scattering (MEIS) have been used to reveal distortions in the crystal lattice of La0.67Ba0.33MnO3 (LBMO) films formed in relaxation of mechanical stresses. The LBMO films 25 nm thick have been prepared by laser deposition. The XRD and MEIS data obtained suggest that biaxially and mechanically elastically stressed LBMO layers grow coherently on LSATO substrates, whose crystal lattice parameter differs only weakly from the corresponding LBMO parameter, whereas in the bulk of manganite films grown on LaAlO3 substrates, stresses relax partially. Stresses do not relax in the LBMO interface about 4 nm thick adjoining LaAlO3. The electro- and magneto-transport parameters of partially relaxed LBMO films have been compared with those obtained for coherently grown manganite films with approximately the same tetragonal distortion of the lattice cell (a (aSyen)/a (aEuro-) = 1.024-1.030; a (aEuro-) and a (aSyen) are the unit cell parameters in the substrate plane and normal to it, respectively). At temperatures substantially lower than the Curie temperature, the electrical resistivity rho of LBMO films fits the relation rho = rho(0) + rho(1) T (2) + rho(2)(H)T (4.5); the coefficients rho(0) and rho(1) do not depend on temperature T and magnetic field, and rho(2) does not depend on temperature but almost linearly decreases with increasing magnetic field strength H. The coefficient rho(2) for partially relaxed LBMO films is substantially larger than that for coherently grown manganite layers.

The superconducting current induced by the penetration of the long-range triplet component of superconducting correlations into a composite ferromagnetic interlayer has been detected in mesa-heterostructures based on oxide cuprate superconductors YBa2Cu3O7 - delta and Au/Nb bilayer films with the composite oxide interlayer that is made of ferromagnetic films of manganite La0.7Sr0.3MnO3 and ruthenate SrRuO3 and has a thickness much larger than the length of correlations determined by the exchange field. The deviation of the superconducting current in the mesa-heterostructure with the fraction of the second harmonic of 13% from a sinusoidal current-phase relation has been detected; this deviation can also be due to the generation of the triplet component of superconducting correlations in the ferromagnet.

The bonding of Ti–6Al–4V to low alloy steel (AISI4330) using SPS technique in the 850–950 °C temperature range was examined. The formation of a thin (∼1 μm) titanium carbide interfacial layer was observed with a thickness only slightly dependent on the joining temperature. This layer separates the joined metals and prevents the formation of Fe–Ti intermetallics in the bonding zone. The maximal tensile strength of the joints (of about 250 MPa) was achieved for bonding at 950 °C for 3.6 ks. The formation of the titanium carbide layer and its evolution are discussed based on the isothermal section of the ternary Fe–Ti–C phase diagram.

The unique combination of SiC properties opens the ways for a wide range of SiC-based industrial applications. Dense silicon carbide bodies (3.18±0.01 g/cm 3 ) were obtained by an SPS treatment at 2050 °C for 10 min using a heating rate of 400 °C/min, under an applied pressure of 69 MPa. The microstructure consists of fine, equiaxed grains with an average grain size of 1.29±0.65 μm. TEM analysis showed the presence of nano-size particles at the grain boundaries and at the triple-junctions, formed mainly from the impurities present in the starting silicon carbide powder. The HRTEM examination revealed high angle and clean grain boundaries. The measured static mechanical properties ( H V =32 GPa, E =440 GPa, σ b =490 MPa and K C 6.8 MPa m 0.5 ) and the Hugoniot Elastic Limit (HEL=18 GPa) are higher than those of hot-pressed silicon carbide samples.

The interface between two wide band-gap insulators, LaAlO3 and SrTiO3 (LAO/STO) offers a unique playground to study the interplay and competitions between different ordering phenomena in a strongly correlated two- dimensional electron gas. Recent studies of the LAO/STO interface reveal the inhomogeneous nature of the 2DEG that strongly influences electrical-transport properties. Nanowires needed in future applications may be adversely affected, and our aim is, thus, to produce a more homogeneous electron gas. In this work, we demonstrate that nanostructures fabricated in the quasi-2DEG at the LaAlO3/SrTiO3 interface, capped with a SrCuO2 layer, retain their electrical resistivity and mobility independent of the structure size, ranging from 100 nm to 30 mu m. This is in contrast to noncapped LAO/STO structures, where the room-temperature electrical resistivity significantly increases when the structure size becomes smaller than 1 mu m. High-resolution intermodulation electrostatic force microscopy reveals an inhomogeneous surface potential with "puddles" of a characteristic size of 130 nm in the noncapped samples and a more uniform surface potential with a larger characteristic size of the puddles in the capped samples. In addition, capped structures show superconductivity below 200 mK and nonlinear currentvoltage characteristics with a clear critical current observed up to 700 mK. Our findings shed light on the complicated nature of the 2DEG at the LAO/STO interface and may also be used for the design of electronic devices.

A combination of the high damage tolerance of TRIP-steel and the extremely low thermal conductivity of partially stabilized zirconia (PSZ) can provide controlled thermal-mechanical properties to sandwich-shaped composite specimens comprising these materials. Sintering the (TRIP-steel-PSZ)/PSZ sandwich in a single step is very difficult due to differences in the sintering temperature and densification kinetics of the composite and the ceramic powders. In the present study, we successfully applied a two-step approach involving separate SPS consolidation of pure (3Y)-TZP and composites containing 20 vol % TRIP-steel, 40 vol % Al2O3 and 40 vol % (3Y)-TZP ceramic phase, and subsequent diffusion joining of both sintered components in an SPS apparatus. The microstructure and properties of the sintered and bonded specimens were characterized. No defects at the interface between the TZP and the composite after joining in the 1050–1150 °C temperature range were observed. Only limited grain growth occurred during joining, while crystallite size, hardness, shear strength and the fraction of the monoclinic phase in the TZP ceramic virtually did not change. The slight increase of the TZP layer’s fracture toughness with the joining temperature was attributed to the effect of grain size on transformation toughening.

The effects of lithium doping on the sintering and grain growth of non-stoichiometric nano-sized magnesium aluminate spinel were studied using a spark plasma sintering (SPS) apparatus. Li-doped nano-MgO·nAl2O3 spinel (n = 1.06 and 1.21) powders containing 0, 0.20, 0.50 or 1.00 at. % Li were synthesized by the solution combustion method and dense specimens were processed using a SPS apparatus at 1200 °C and under an applied pressure of 150 MPa. The SPS-processed samples showed mutual dependency on the lithium concentration and the alumina-to-magnesia ratio. For example, the density and hardness values of near-stoichiometry samples (n = 1.06) showed an incline up to 0.51 at. % Li, while in the alumina rich samples (n = 1.21), these values remained constant up to 0.53 at. % Li. Studying grain growth revealed that in the Li-MgO·nAl2O3 system, grain growth is limited by Zener pining. The activation energies of undoped, 0.2 and 0.53 at. % Li-MgO·1.21Al2O3 samples were 288 ± 40, 670 ± 45 and 543 ± 40 kJ·mol−1, respectively.

The study deals with the effect of the SPS parameters and LiF doping on the mechanical and optical properties polycrystalline magnesium aluminate spinel (PMAS) with emphasis on the grain size of the final product. Sintering at 1300°C of undoped powder yielded fully dense submicrometer (0.4–0.6 μm) samples with elevated mechanical properties (1600HV and 300MPa bending strength). Doped samples had a larger, 40 μm grain size, lower, 1450HV, hardness and 150MPa bending strength. The transmittance of the doped samples (80% at 500 nm wavelength) was higher than that of the undoped ones. Thus, the required functionality of the ceramic dictates the choice of parameters for the fabrication of dense transparent PMAS.

Transparent 1 at.% Nd:YAG ceramics were fabricated by spark plasma sintering (SPS) from nanometric Nd:YAG powders, both undoped and pre-mixed with 0.25 wt.% LiF additive. The mechanical and optical properties of the consolidated samples were determined as a function of the processing parameters, namely holding time, peak sintering temperature and heating rate. The presence of LiF accelerates densification and grain growth. Hardness and bending strength are decreased in the presence of the LiF additive, in consistence with the increase of the grain size. The optical transmittance in the doped samples sintered at 1400 °C, reaches 97% of the theoretical transmission and is significantly higher than that of the undoped samples. The increased optical transmittance of the doped samples is attributed to pore elimination by enhanced mass transport and cleansing of the carbon contamination by the fluorine component of the LiF additive. The presence of the latter has no effect on the absorption spectrum of the Nd:YAG ceramic.

Electrical transport and microstructure of interfaces between nm-thick films of various perovskite oxides grown by pulsed laser deposition (PLD) on TiO2- terminated SrTiO3 (STO) substrates are compared. LaAlO3/STO and KTaO3/STO interfaces become quasi-2DEG after a critical film thickness of 4 unit cell layers. The conductivity survives long anneals in oxygen atmosphere. LaMnO3/STO interfaces remain insulating for all film thicknesses and NdGaO3/STO interfaces are conducting but the conductivity is eliminated after oxygen annealing. Medium-energy ion spectroscopy and scanning transmission electron microscopy detect cationic intermixing within several atomic layers from the interface in all studied interfaces. Our results indicate that the electrical reconstruction in the polar oxide interfaces is a complex combination of different mechanisms, and oxygen vacancies play an important role.

Heterostructures consisting of a cuprate superconductor YBa2Cu3O7x and a ruthenate/manganite (SrRuO3/La0.7Sr0.3MnO3) spin valve have been studied by SQUID magnetometry, ferromagnetic resonances and neutron reflectometry. It was shown that due to the influence of magnetic proximity effect a magnetic moment is induced in the superconducting part of heterostructure and at the same time the magnetic moment is suppressed in the ferromagnetic spin valve. The experimental value of magnetization induced in the superconductor has the same order of magnitude with the calculations based on the induced magnetic moment of Cu atoms due to orbital reconstruction at the superconductor-ferromagnetic interface. It corresponds also to the model that takes into account the change in the density of states at a distance of order of the coherence length in the superconductor. The experimentally obtained characteristic length of penetration of the magnetic moment into superconductor exceeds the coherence length for cuprate superconductor. This fact points on the dominance of the mechanism of the induced magnetic moment of Cu atoms due to orbital reconstruction., 20 pages, 9 figures

The high strain rate behavior of Spark Plasma Sintered (SPS) magnesium aluminate spinel (spinel) disc-shaped samples was studied under parallel (planar impact) and divergent (spherical impact) flow conditions. The results of planar impact experiments allowed determining the principal Hugoniot up to 40-GPa compressive stress. The Hugoniot Elastic Limit (HEL) ranged from 10.8 to 12.2 GPa and increases slightly with the magnitude of the impact. The spall strength determined in low-velocity impact experiments has a 0.63-GPa maximum at an impact stress of 1.7 GPa and vanishes completely as the impact stress exceeds 2.1 GPa. The spherical impact tests (convex copper impactors with radii of curvature from 45 to 550 mm and velocities from 290 to 570 m/s) were carried out in parallel with AUTODYN-2D numerical simulations of the experimentally recorded velocity histories. The results allowed establishing the compressive failure threshold surface of spinel in the principal stress space. At a transverse stress of 2.4 GPa, the failure threshold undergoes a change of the dominant mode of the inelastic deformation from brittle cracking to some form of ductile yielding.

We present a novel room temperature bolometer with nanosecond response that can be used both for coherent and incoherent detection through the entire terahertz frequency range. A responsivity of up to 15 V/W, and a noise equivalent power (NEP) ~ 450 pW/Hz0.5 were measured at modulation frequencies from 0.5 kHz to 100 kHz. A conversion gain of -28 dB was demonstrated at an intermediate frequency of 20 MHz with a Local Oscillator power of 0.74 mW. Possible improvements of the bolometer characteristics are discussed.

Fabrication of dense nanocrystalline TiC by spark plasma sintering was studied. TiC nano-particles 34 nm in size were densified by spark plasma sintering at 100 MPa for 5 min between 1100 °C and 1700 °C. The density linearly increased between 1100 °C and 1500 °C from 72% to 97%. Density of 98% was reached at 1700 °C compared to 76% for the micrometer size reference powder. The main densification occurred during the heating and resulted in nanocrystalline to submicrometer size grains. Lattice parameter decreased and Ti/C ratio increased with the temperature from stoichiometric TiC (1.17) towards that of Ti 2 C (1.77). A unique layered microstructure in regions a few tens to hundreds of micrometer in size, composed of TiC/Ti 2 C, resembled the flow pattern characteristic of cooperative particle sliding in granular materials.

Sr3Ru2O7/Sr2RuO4 eutectic system is investigated by electron backscattering diffraction (EBSD) and X-ray diffraction (XRD). The eutectic growth enables the solidification of the two phases in an ordered lamellar pattern extending along the growth direction, namely the b-axis direction. The eutectic material thus provides in the a-c plane two distinct interfaces having different microstructures with respect to the growth direction. Our analysis shows that, across the inplane c-axis direction (characterized by a poor lattice matching), the b-axis orientation is not constant at the individual interfaces, showing an orientation spread of about 5 degrees. However, across the in-plane a-axis direction (characterized by a good lattice matching), the b-axis orientation does not change within a few tenths of degree (about 0.25 degrees). Such information at nanoscale is also verified on a macroscopic level by standard XRD investigation.

Nano-size YAG powder co-mixed with 0.25 wt.% LiF was used to fabricate transparent polycrystalline YAG specimens by means of the Spark Plasma Sintering (SPS) technique. The presence of the LiF additive in the initial nano-powder allows obtaining fully dense disc shaped (up to 4 mm thick) transparent specimens at the outcome of a 2 h treatment at 1300 °C. The presence of LiF plays a key role in the mass transport related effects during the densification of YAG to full density and also in the elimination of the residual carbon contamination, allowing reaching a level of optical transmittance close to the theoretical value.

Polycrystalline magnesium aluminate (MgAl2 O4 ) spinel (PMAS) exhibits a unique combination of physical, chemical, mechanical, and optical properties, which makes it useful for a wide range of applications, including UV lenses for lithography, electroinsulation, and structural windows for both VIS and IR region radiation and armor applications. Conventional two-stage processing of PMAS involves prolonged pressureless sintering followed by hot isostatic pressing. The costly processing of high-quality transparent PMAS ceramic is the main reason for the limited usage of this material in industry. Spark plasma sintering (SPS) is a relatively novel one-stage, rapid, and cost-effective sintering technique, which holds great potential for producing high-quality optical materials. Here, recent advances in the fabrication of transparent PMAS by the SPS approach, the influence of sintering parameters on microstructure evolution during densification, and their effects on the optical and mechanical properties of the material are reviewed.

Surface potential distributions in ultra-thin (0.8-3.9 nm) LaAlO3 layers deposited on SrTiO3 substrates are studied. It is found that the potential distribution evolves from island-like to a homogeneous one with increasing LaAlO3 thickness. It is suggested that the observed islands are caused by a locally enhanced concentration of mobile charge carriers at the interface that is, in turn, related to non-stoichiometry of the layers with thickness bellow 4 unit cells. Transition to a homogeneous potential distribution with increasing LAO thickness (≥4 unit cells) corresponds to the formation of a quasi-2-dimensional electron gas. The results agree with a percolation model explaining the insulator-to-metal transition that occurs at the LaAlO3/SrTiO3 heterointerface.

Fully dense boron carbide specimens were fabricated by the spark plasma sintering (SPS) technology in the absence of any sintering additives. Densification starts at 1500 °C and the highest densification rate is reached at about 1900 °C. The microstructure of the ceramic sintered at 2200 °C, with heating rates in the 50–400 °C/min range, displays abnormal grain growth, while for a 600 °C/min heating rate a homogeneous distribution of finely equiaxed grains with 4.05 ± 1.62 μm average size was obtained. TEM analysis revealed the presence of W-based amorphous and of crystalline boron-rich B 50 N 2 secondary phases at triple-junctions. No grain-boundary films were detected by HRTEM. The formation of a transient liquid alumino-silicate phase stands apparently behind the early stage of densification.

Mixtures of elementary oxides, MgO-Al 2 O 3 , were used to fabricate transparent polycrystalline magnesium aluminate spinel specimens by means of the spark plasma sintering technique. A sintering aid, 1 wt% of LiF, was added to the mixed powder. The presence of the additive promotes the synthesis of spinel that starts at 900°C and is completed at 1100°C. The LiF additive wets spinel on its melting and promotes densification, which is completed at 1600°C. LiF vapor plays a cardinal role in eliminating residual carbon contamination and in the fully dense state, allows attaining a 78% level of optical transmittance. The optimal conditions for achieving adequate transparency were determined and the role of the LiF addition in the various stages of the process is discussed.

We have re-assessed different methods to obtain single terminated perovskite oxide Substrate Surfaces of SrTiO(3), LaAlO(3) and NdGaO(3). The Surfaces have been probed by a combination of atomic and lateral force microscopy, X-ray photoelectron spectroscopy and reflection high-energy electron diffraction. (0 0 1)SrTiO(3) surfaces were prepared with HF or plasma etching and annealing, (0 0 1)LaAlO(3) Surfaces were prepared with or Without HCl etching and a consecutive annealing at 750-1100 degrees C, and (1 1 0)NdGaO(3) surfaces were only annealed. Two of the recipes have previously been suggested to result in A-site terminated Surfaces. However, except for the case of high-temperature annealed LaAlO(3) where we observe a double-terminated Surface, our data Suggest that the single terminated surfaces obtained by these methods were of B-site type.

A laboratory prototype RF amplifier for the frequency range 1–10 GHz is designed, created, and tested. The device is based on high-temperature superconducting quantum interference filters (SQUIFs) and the technology of bicrystalline substrates. The main characteristics of the prototype SQUIF amplifier are numerically simulated and measured.