Mitsubishi Materials

In first-principles-based calculations of thermodynamic quantities "thermodynamic consistency" has not been guaranteed when applying disparate approximation methods to diverse phases such as, compounds, solid solutions, or liquids, constituting alloy phase diagrams. In this study, we performed tailored calculations for each phase in the Cu-Ni-Si system and verified consistency using phase equilibrium calculations and likelihood analysis. The resulting phase diagrams generally reproduced experimental ones, despite extreme sensitivity to minute free energy differences. Furthermore, likelihood analysis quantitatively demonstrated that free energy residuals fall within a narrow 1-2 kJ/mol range. This indicates that a high degree of thermodynamic consistency is preserved across all phases. Therefore, we newly define the computational process encompassing the first-principles uncertainty revealed by this likelihood analysis as the “theoretical phase diagram calculation method.” By applying this method to the binaries and ternary of the Cu-Ni-Si system, we demonstrated its capability to reproduce experimental phase diagrams with high precision.

Machine-learning-based AI prediction drives rising electricity use and processing demands, raising sustainability concerns. Reservoir computing reduces training by optimizing only output weights, and physical reservoir computing (PRC) further accelerates processing by exploiting physical phenomena. Yet, many hysteresis-based PRCs depend on costly or unstable materials and fabrication methods unsuited to scale, limiting practical deployment. This study evaluated the potential of all-solid-state electric double-layer (EDL) thin-film transistors, incorporating a lanthanum zirconium oxide solid electrolyte and an indium oxide semiconductor, for PRC applications. The drain current (ID) and gate current (IG) as functions of gate voltage (VG) displayed pronounced hysteresis, with the extent of hysteresis dependent on both the drain voltage (VD) and the VG scanning rate. The ID response to pulsed VG inputs demonstrated a clear dependence on the preceding input pulse VG, thereby validating the device's short-term memory properties. In the second-order nonlinear autoregressive moving average task, the minimum normalized mean square error (NMSE) was 7.71 × 10−3 and 7.56 × 10−3 when utilizing the IG response as virtual nodes comprising 40 and 80 points, respectively. Furthermore, the NMSE demonstrated a strong correlation with memory capacity, particularly with the coefficient of determination associated with the correlation for up to two previous data points. The all-solid-state EDL-TFT-based physical reservoir, with its miniaturization, air stability, and broad pulse operating range, offers a scalable and robust platform that could enable practical integration of PRC into next-generation AI devices, advancing energy-efficient and durable hardware solutions.

The mechanism governing the resistivity in dilute Cu-3d transition-metal alloys at ambient temperature – the regime relevant to most practical applications and distinct from the low-temperature, Kondo-screened regime addressed by earlier theoretical work – is investigated using first-principles calculations based on the Korringa–Kohn–Rostoker coherent potential approximation combined with the Kubo–Greenwood formalism. The paramagnetic state is described within the disordered local moment (DLM) framework, corresponding to a local-moment paramagnet rather than a Pauli paramagnet. We show that the experimentally observed resistivity trends are reproduced only within the DLM description, while nonmagnetic and ferromagnetic states fail to capture the correct element dependence. Contrary to conventional interpretations based on the density of states at the Fermi level, the resistivity exhibits a strong correlation with the full width at half maximum (FWHM) of the Bloch spectral function (BSF) on the Fermi surface. This correlation reflects the disorder-induced lifetime broadening of electronic states, directly related to the scattering rate that governs electrical resistivity. A common power-law scaling between resistivity and BSF broadening is identified across different magnetic states. These results demonstrate that the resistivity is governed by disorder-induced band broadening in momentum space rather than by local density-of-states effects, providing a unified microscopic interpretation of the breakdown of Linde's rule in Cu-based alloys.

In recent years, copper-based conductive and heat dissipation components have required fine structures for miniaturization and enhanced functionality. Micro-forming is an excellent processing method characterized by high productivity and suitability for mass production. Since small workpieces can be formed within a short stroke in micro-extrusion, it is important to understand the deformation behavior immediately after the start of extrusion. However, before steady state is attained, the evolution of microstructure and plastic flow with stroke progression during non-steady-state deformation has not yet been sufficiently clarified. In this study, to investigate the effect of changes in plastic flow on force behavior, micro-extrusion tests were conducted using pure copper. The geometric and crystallographic characteristics of the deformation structure were then analyzed. The extrusion force behavior exhibited three distinct stages, including a peak of the force. The force peak was attributed to changes in plastic flow associated with the deformation structure formed at the sample tip immediately after the start of extrusion. This change leads to the evolution of the effective extrusion ratio, which significantly influences the force response during non-steady-state deformation.

In order to clarify the high-temperature deformation mechanisms of WC-Co cemented carbides, the strain-rate sensitivity m and the apparent activation volume nu(a) were measured for WC-10mass%Co and WC-15mass%Co cemented carbides with different WC grain sizes, at strain rates between 10(-4) and 10(-3) s(-1) and temperatures between 973 and 1273 K. The coarse-grained cemented carbides exhibited m values of 0.03-0.08, and the apparent activation volume nu(a) increased monotonically with decreasing stress, reaching values of 5-10 b(3), where b is the magnitude of the Burgers vector of WC. The fine-grained cemented carbides showed deformation behavior similar to that of the coarse-grained cemented carbides in the high-stress region; however, in the low-stress region, m exceeded 0.10 and nu(a) decreased to 2-3 b(3). These results indicate that plastic deformation is mainly governed by dislocation glide in the WC phase in the high-stress region for the fine-grained cemented carbides and over the entire stress range for the coarse-grained cemented carbides, whereas in the low-stress region for the fine-grained cemented carbides, plastic deformation is mainly governed by dislocation creep of the WC phase. Furthermore, a relationship was established between the transition stress sigma(trans), at which the rate-limiting deformation mechanism changes from dislocation glide to dislocation creep, and the cobalt volume fraction as well as the WC grain size. These relationships provide a useful guideline for material design aimed at suppressing plastic deformation in cemented carbides.