Thermal and mechanical properties of LaNbO4-based ceramics

Thermal and mechanical properties of polycrystalline La_1−xA_xNbO₄ (x = 0, 0.005, 0.02 and A = Ca, Sr and Ba) are reported. The materials possess a ferroelastic to paraelastic phase transition close to 500 °C, and the linear thermal expansion is significantly lower (8.6 ± 0.5 × 10⁻⁶ °C⁻¹) for the paraelastic phase compared to the ferroelastic phase (15 ± 3 × 10⁻⁶ °C⁻¹). The hardness was significantly higher for acceptor doped materials (6 GPa) compared to pure LaNbO₄ (3 GPa) due to a significantly smaller average grain size. The fracture toughness of La_0.98Sr_0.02NbO₄, measured by single edge V-notched beam method, was 1.7 ± 0.2 MPa m^1/2 independent of temperature up to 600 °C. The ferroelastic properties of the materials were confirmed by non-linear relationships between stress and strain during compression/decompression, a remnant strain after decompression and the presence of ferroelastic domains. The mechanical properties of LaNbO₄-based materials are discussed with focus on ferroelasticity, microcracking due to crystallographic anisotropy and pinning of ferroelastic domain boundaries.     

Chemical compatibility of proton conducting LaNbO4 electrolyte with potential oxide cathodes

The chemical and physical compatibility of the proton conducting electrolyte material LaNbO₄ with the potential partner materials LaMO₃ (MMn, Fe, Co) and La₂NiO₄ is investigated via the reaction of fine-grained powders and solid-state diffusion couples. Results show generally good chemical compatibility for LaNbO₄ with perovskite type compositions, particularly the LaFeO₃ and LaMnO₃ systems. In contrast, Ruddlesden–Popper type phases are predicted to be poor candidates for use with LaNbO₄. Investigation of the La₂O₃–NiO–Nb₂O₅ and La₂O₃–CoO–Nb₂O₅ phase diagrams finds two new perovskite-related materials of stoichiometry LaNb_1/3M_2/3O₃ (MNi, Co), and indicates coexistence of LaNbO₄ with the binary oxides NiO and CoO. Additionally, reduction of a LaNbO₄–NiO composite confirms coexistence of LaNbO₄ with Ni, and so it is concluded that doped-LaMO₃|LaNbO₄|Ni-LaNbO₄ type electrochemical cells may be manufactured via a direct co-firing route without the formation of secondary phases at inter-phase boundaries.     

Processing of thin film ceramic membranes for oxygen separation

Processing of dense and thin ceramic membrane layers for high temperature selective oxygen separation is addressed in this study. Mixed oxygen-ionic and electronic conducting perovskite oxide system based on La_0.2Sr_0.8Fe_0.8Ta_0.2O_3−δ composition is employed for processing of structural and functional layers. Special focus is aimed at obtaining thin layer and final microstructure with particle size in the sub-micron range. Thin layer deposition is performed by dip coating technique using stable colloidal suspension of perovskite particles dispersed within ethanol media. Two polymer based surfactants were screened for their effect on particle agglomeration and rheological response. By using optimum quantity of 2.5 wt.% addition of selected surfactant it is possible to obtain dense 15-60 μm thick functional layers. The thermal cycle applied resulted in final particle sizes within sub-micron range. By employing suspension with pore former it was possible to significantly increase the surface area of the functional layer.     

Verifying task-based specifications in conceptual graphs

A conceptual model is a model of real world concepts and application domains as perceived by users and developers. It helps developers investigate and represent the semantics of the problem domain, as well as communicate among themselves and with users. In this paper, we propose the use of task-based specifications in conceptual graphs (TBCG) to construct and verify a conceptual model. Task-based specification methodology is used to serve as the mechanism to structure the knowledge captured in the conceptual model; whereas conceptual graphs are adopted as the formalism to express task-based specifications and to provide a reasoning capability for the purpose of verification. Verifying a conceptual model is performed on model specifications of a task through constraints satisfaction and relaxation techniques, and on process specifications of the task based on operators and rules of inference inherited in conceptual graphs.     

Synthesis, densification and electrical properties of strontium cerate ceramics

Powders of pure and 5% ytterbium substituted strontium cerate (SrCeO₃/SrCe_0.95Yb_0.05O_3−δ) were prepared by spray pyrolysis of nitrate salt solutions. The powders were single phase after calcination in nitrogen atmosphere at 1100 °C (SrCeO₃) and 1200 °C (SrCe_0.95Yb_0.05O_3−δ). Dense SrCeO₃ and SrCe_0.95Yb_0.05O_3−δ materials were obtained by sintering at 1350–1400 °C in air. Heat treatment at 850 and 1000 °C, respectively, was necessary prior to sintering to obtain high density. The dense materials had homogenous microstructures with grain size in the range 6–10 μm for SrCeO₃ and 1–2 μm for SrCe_0.95Yb_0.05O_3−δ. The electrical conductivity of SrCe_0.95Yb_0.05O_3−δ was in good agreement with reported data, showing mixed ionic–electronic conduction. The ionic contribution was dominated by protons below 1000 °C and the proton conductivity reached a maximum of 0.005 S/cm above 900 °C. In oxidizing atmosphere the p-type electronic conduction was dominating above 700 °C, while the contribution from n-type electronic conduction only was significant above 1000 °C in reducing atmosphere.     

SiGe heterostructure field-effect transistor using V-shaped confining potential well

A working p-type SiGe heterostructure field-effect transistor, utilizing a V-shaped confining potential well as the conducting channel, has been successfully fabricated. The upper boron /spl delta/-doping layer acts as a diffusion barrier to slow diffusion into the undoped Si cap layer. On the other hand, the bottom boron /spl delta/-doping layer prevents hot holes from escaping the channel by improving carrier confinement. It is found that when a V-shaped confining potential well is used as the conducting channel, the devices exhibit the excellent property not only of higher current density but also enhancement in extrinsic transconductance and linear operation range over a wider dynamic range than those of /spl delta/-doped devices for the same dose in SiGe conducting well. The measured transconductance is enhanced three to six times over that of the other /spl delta/ cases.     

A novel verifiable secret sharing mechanism using theory of numbers and a method for sharing secrets

Verifiable secret sharing (VSS) has been extensively used as a cryptographic tool in many applications of information security in recent years. A VSS enables a dealer to divide a secret s into n shares and allows shareholders to verify whether their shares are generated by the dealer consistently without revealing the secrecy of both shares and the secret. More specifically, shareholders can verify that (i) the secret can be recovered by any t or more than t shares and (ii) the secret cannot be obtained by fewer than t shares. Many VSSs are based on polynomial, and only a few of them are based on the Chinese Remainder Theorem (CRT). Recently, Harn et al. proposed a CRT‐based VSS in which multiple verification secrets are used during the phase of verification. In this paper, we propose a VSS based on Asmuth‐Bloom's (t, n) SS scheme, which depends on the CRT. Our proposed VSS is simpler and more efficient than the scheme of Harn et al. Our proposed VSS is unconditionally secure. Copyright © 2014 John Wiley & Sons, Ltd.     

Multipartite Secret Sharing Based on CRT

Secure communication has become more and more important for system security. Since avoiding the use of encryption one by one can introduce less computation complexity, secret sharing scheme (SSS) has been used to design many security protocols. In SSSs, several authors have studied multipartite access structures, in which the set of participants is divided into several parts and all participants in the same part play an equivalent role. Access structures realized by threshold secret sharing are the simplest multipartite access structures, i.e., unipartite access structures. Since Asmuth–Bloom scheme based on Chinese remainder theorem (CRT) was presented for threshold secret sharing, recently, threshold cryptography based on Asmuth–Bloom secret sharing were firstly proposed by Kaya et al. In this paper, we extend Asmuth–Bloom and Kaya schemes to bipartite access structures and further investigate how SSSs realizing multipartite access structures can be conducted with the CRT. Actually, every access structure is multipartite and, hence, the results in this paper can be seen as a new construction of general SSS based on the CRT. Asmuth–Bloom and Kaya schemes become the special cases of our scheme.     

Enhanced CMOS performances using substrate strained-SiGe and mechanical strained-Si technology

We developed a novel CMOS architecture that uses mechanical tensile stress, induced by the Si nitride-capping layer, together with the pseudomorphic compressive stress in SiGe layer to improve the drive current of both n- and pMOSFETs simultaneously. The unique advantage of this process flow is that on the same wafer, individual MOSFET performance can be adjusted independently to their optimum due to the separation process for two type devices. It is found that n- and pMOSFETs in the novel CMOS architecture behaved better in performance, not only a higher drain-to-source saturation current but also higher transconductance with wide gate voltage swing, than the Si-control devices, thus making this flow to show a great flexibility for developing next-generation high-performance CMOS.