Dynamic transition processes of defects within microstructures govern most of the mechanical deformation behaviour in materials. However, quantifying them remains challenging, especially within microscopic volumes. In this work, dynamic frequency sweep experiments on micrometer-sized cantilevers fabricated by focused ion beam milling from single-crystalline W are presented as a model material system for microstructural defect quantification. The resulting mechanical spectra show the indenter-inherent resonance peak as well as auxiliary features, which cannot be explained by external structural relaxations in the load train. Using a classical Arrhenius-type framework, activation volumes ranging from 0.26 to 1.89 b3 have been found for these features and compared with density functional theory calculations. The results suggest that the observed features correspond most likely to microstructural defects, with experimental values in a reasonable order-of-magnitude, underlining the possibility to measure such fundamental processes also within microscopic features.
The temperature-dependent compressive deformation behavior of a lamellar γ-Ni/Ni5Zr near-eutectic Ni88.3Zr7.7Al4 (at σ_y ) across the investigated temperature range, decreasing gradually from σ_y =1203 ± 15 MPa at room temperature to σ_y =630 ± 14 MPa at 850 °C, due to combination of stable phase constitution, constrained lamellar geometry, and diffusion-assisted recovery while sustaining large compressive strains without fracture at ≥ 500 °C. Microstructural observations reveal that a temperature-dependent interface instability mechanisms at lamellar terminations play important role for strength retention with sustained plastic flow. Kocks–Mecking analysis identifies a transition from dislocation storage-dominated hardening to recovery-controlled flow near 500 °C, which is consistent with the observed fracture-to-flow transition. The results provide quantitative insight into the deformation mechanisms governing high-temperature performance of γ-Ni/Ni5Zr eutectic alloys.
Deformation mechanism and microstructural evolution of a novel Ti–12Al–4Nb–2.3Cr–2Zr titanium alloy were systematically investigated based on hot workability under deformation temperatures of 700–1000 °C and strain rates of 0.0005–0.5 s−1. By combining the processing map with metallographic observations, a preferred hot-working window is identified as approximately 900–1000 °C and 0.0005–0.005 s−1. At high strain rates and low deformation temperatures, lamellar α phase mainly undergoes bending and rotation. Spheroidization of α phase is favored under high deformation temperatures and low strain rates, whereas uniform coarsening predominates under low deformation temperatures and low strain rates. Two dynamic recrystallization mechanisms, namely continuous dynamic recrystallization associated with progressive subgrain rotation and discontinuous dynamic recrystallization dominated by grain boundary migration, coexist during hot compression of TiAlNbCrZr alloy.
A spinel-type sulfide, ZnSc2S4, is a recently identified semiconductor promising for optoelectronics. We report anomalous thermopower polarity switching induced in Ti-doped ZnSc2S4, Zn(Sc1−xTix)2S4. While undoped ZnSc2S4 is a robust insulator, Ti doping monotonically enhances electrical conductivity. In contrast, the Seebeck coefficient (S) exhibits anomalous behavior: while Zn(Sc1−xTix)2S4 with high x possesses large negative S, its magnitude decreases with decreasing x. Moreover, further decreasing x causes S to cross zero into the positive region, demonstrating a transition from insulating to p-type and ultimately n-type behavior with increasing x. Optical and hard X-ray photoelectron spectroscopy reveal doping-induced sub-gap states and firm pinning of the Fermi level (EF), inconsistent with the conventional rigid-band picture. Based on these analyses, we propose a possible mechanism: conduction associated with these sub-gap states gives rise to the anomalous polarity switching, with the pinned EF located on different tails of the sub-gap structure for p- and n-type conduction.
Wide- and ultrawide-band gap wurtzite III nitrides are commonly alloyed with group-3 elements such as Sc, Y, and Gd to reduce the polarization switching coercive field ( E_c ) for ferroelectrics. Because group-3 nitrides typically adopt the rocksalt structure with relatively small band gaps, alloying is generally expected to reduce both the band gap ( E_g ) and dielectric breakdown field ( E_b ). However, recent reports of band gap widening in Ga _1-x Sc _x N and In _1-x Sc _x N challenge this assumption. Using DFT calculations, we show that band gaps in heterostructural III-nitride alloys are governed not only by the ground-state polymorph but also by structurally relevant polymorphs of the alloying end member. Extending the analysis to AlN-, GaN-, and InN-based alloys with Sc, Y, La, and B, we identify three distinct band gap regimes that follow wurtzite-, hexagonal-BN-, or rocksalt-like trends. These behaviors are governed by bond ionicity and structural distortion, providing design guidelines for engineering E_g and implication for E_b in wurtzite III-nitride alloys.
