Junping Xi

Spatially selective thermal regulation of multijunction piezoelectric structures requires the control of both the local junction response and coupling between neighboring junctions. A finite-length analytical model is developed for a symmetric piezoelectric sandwich fiber with PNP or NPN doping under a prescribed local temperature change. Within a static, closed, one-dimensional weak-junction approximation, the solution separates the reference junction field from the thermally induced polarization response and accounts for carrier screening and global carrier conservation. Finite-element and nonlinear drift calculations assess solution accuracy and the carrier linearization. Centered heating reduces one junction field while enhancing the other, whereas independently controlled thermal regions enable simultaneous point cancelation through their differential response. In the representative weak-junction case, opposite temperature increments of approximately 0.0165 K cancel the two-junction point fields; minimizing the field over finite junction neighborhoods instead leaves approximately 30% of the reference root-mean-square field. Fixed-interval potential differences further show that point cancelation does not eliminate the electrical response across a junction neighborhood. Thermal spreading and constitutive uncertainty shift the required temperature settings. The prescribed carrier populations do not represent dark-equilibrium ZnO at room temperature. The resulting control relations characterize an idealized weak-junction system, rather than a validated semiconductor device, and provide conditional guidance for thermal-source placement and control-target selection.

The structural, mechanical, dislocation, and electronic properties of the Sc₃AlC MAX phase under applied pressure are investigated in detail using first-principles calculations. Key parameters, including lattice parameter ratios, elastic constants, Young’s modulus, bulk modulus, shear modulus, brittle-to-ductile behavior, Poisson’s ratio, anisotropy, Cauchy pressure, yield strength, Vickers hardness, and energy factors, are systematically analyzed as a function of applied pressure. The results demonstrate that the Sc₃AlC MAX phase exhibits remarkable mechanical stability within the pressure range of 0 to 60 GPa. Notably, applied pressure markedly improves its mechanical properties, such as resistance to elastic, bulk, and shear deformations. The B/G ratio suggests a tendency toward ductile behavior with increasing pressure, and the negative Cauchy pressure indicates the directional characteristics of interatomic bonding in nature. Vickers hardness and yield strength increase under pressures of 0 to 10 GPa and then decrease sharply above 50 GPa. High pressure suppresses dislocation nucleation due to the increased energy factors, along with twinning deformation. Furthermore, electronic structure analysis confirms that high pressure enhances the interatomic bonding in the Sc₃AlC MAX phase, while the enhancement effect is not substantial. This study offers critical insights for designing MAX phase materials for extreme environments, advancing applications in aerospace and electronics fields.