Extended planar defects of oxygen vacancies in ferroelectric [Formula: see text] and impact on ferroelectricity.

Extended defects of vacancies in ferroelectrics (FE), where vacancies spread over an extended space, are of critical importance in terms of understanding the long-standing problems such as polarization fatigue and aging. However, extended defects in FEs are poorly understood. Here we investigate the extended planar oxygen vacancies in ferroelectric [Formula: see text] using density functional theory and the modern theory of polarization.

An Internet of Things-Oriented Adaptive Mutation PSO-BPNN Algorithm to Assist the Construction of Entrepreneurship Evaluation Models for College Students.

In this paper, the IoT-based adaptive mutation PSO-BPNN algorithm is used to conduct in-depth research and analysis of the entrepreneurship evaluation model for college students and practical applications. This paper details the principle, implementation, and characteristics of each BP algorithm and PSO algorithm. When classifying college students' entrepreneurship evaluation based on BP neural network, because BP algorithm is a local optimization-seeking algorithm, it is easy to fall into local minima in the training phase of the network and the convergence speed is slow, which leads to the reduction of classifier recognition rate.

Persistence of strong and switchable ferroelectricity despite vacancies.

Vacancies play a pivotal role in affecting ferroelectric polarization and switching properties, and there is a possibility that ferroelectricity may be utterly eliminated when defects render the system metallic. However, sufficient quantitative understandings of the subject have been lacking for decades due to the fact that vacancies in ferroelectrics are often charged and polarization in charged systems is not translationally invariant. Here we perform first-principles studies to investigate the influence of vacancies on ferroelectric polarization and polarization switching in prototypical BaTiO of tetragonal symmetry.

Predicted coupling of the electromagnetic angular momentum density with magnetic moments.

Analytical derivations are developed to demonstrate that (i) the angular moment density associated with an electromagnetic field can directly couple with magnetic moments to produce a physical energy, (ii) this direct coupling explains known, subtle phenomena, including some recently predicted in magnetoelectric materials, and (iii) this coupling also results in novel effects, such as the occurrence of a magnetic anisotropy that is driven by antiferroelectricity.

Collective dipole behavior and unusual morphotropic phase boundary in ferroelectric Pb(Zr(0.5)Ti(0.5))O3 nanowires.

Dipole collective behavior and phase transition in ferroelectric (FE) Pb(Zr(0.5)Ti(0.5))O(3) nanowires, caused by modulated electric fields, are reported.

Cooperative response of Pb(ZrTi)O3 nanoparticles to curled electric fields.

We investigate cooperative responses, as well as a microscopic mechanism for vortex switching, in Pb(Zr0.5Ti0.5)O3 nanoparticles under curled electric fields.

Vortex-to-polarization phase transformation path in ferroelectric Pb(ZrTi)O3 nanoparticles.

Phase transformation in finite-size ferroelectrics is of fundamental relevance for understanding collective behaviors and balance of competing interactions in low-dimensional systems. We report a first-principles effective Hamiltonian study of vortex-to-polarization transformation in Pb(Zr0.5Ti0.

Electric-field-induced domain evolution in ferroelectric ultrathin films.

The electric-field-induced evolution of the recently discovered periodic 180 degree nanostripe domain structure is predicted in epitaxial Pb(Zr0.5Ti0.5)O3 ultrathin films from first principles.

Spontaneous polarization in one-dimensional Pb(ZrTi)O3 nanowires.

Formation of spontaneous polarization in one-dimensional (1D) structures is a key phenomenon that reveals collective behaviors in systems of reduced dimensions, but has remained unsolved for decades. Here we report ab initio studies on finite-temperature structural properties of infinite-length nanowires of Pb(Zr0.5Ti0.

Ultrathin films of ferroelectric solid solutions under a residual depolarizing field.

A first-principles-derived approach is developed to study the effects of depolarizing electric fields on the properties of Pb(Zr,Ti)O3 ultrathin films for different mechanical boundary conditions. A rich variety of ferroelectric phases and polarization patterns is found, depending on the interplay between strain and the amount of screening of surface charges. Examples include triclinic phases, monoclinic states with in-plane and/or out-of-plane components of the polarization, homogeneous and inhomogeneous tetragonal states, as well as peculiar laminar nanodomains.

Unusual phase transitions in ferroelectric nanodisks and nanorods.

Bulk ferroelectrics undergo structural phase transformations at low temperatures, giving multi-stable (that is, multiple-minimum) degenerate states with spontaneous polarization. Accessing these states by applying, and varying the direction of, an external electric field is a key principle for the operation of devices such as non-volatile ferroelectric random access memories (NFERAMs). Compared with bulk ferroelectrics, low-dimensional finite ferroelectric structures promise to increase the storage density of NFERAMs 10,000-fold.

Density-functional study of organic-inorganic hybrid single crystal ZnSe(C2H8N2)(1/2).

Unusual properties (i.e., strong band dispersion, high carrier mobility, wide absorption-energy window, and sharp band-edge transition) that are desirable for hybrid-material electronics and for solar electric energy conversion are predicted to exist in the organic-inorganic chalcogenide single crystal ZnSe(C2H8N2)(1/2) by using density-functional calculations.

Ferroelectricity in barium titanate quantum dots and wires.

Properties of BaTiO3 colloidal quantum dots and wires are simulated using a first-principles-based approach. Large atomic off-center displacements (that are robust against capping matrix materials) are found to exist in very small (<5 nm) dots. We further determine the size dependences of electrical and electromechanical responses in the studied nanostructures, as well as provide microscopic understanding of these responses.

First-principles determination of electromechanical responses of solids under finite electric fields.

We describe a first-principles, easy-to-implement, and efficient approach for determining the structural geometry of insulating solids under finite electric fields. This method consists of simultaneously minimizing the field-induced total ionic forces and the electric free energy. Moreover, we present a theory to analyze its predictions that provides a microscopic understanding of electro-mechanical responses in materials.

Crystal of semiconducting quantum dots built on covalently bonded t5 [in(28)cd(6)s(54)](-12): the largest supertetrahedral cluster in solid state.

Periodic array of nanoparticles is essential for practical applications in optical devices. Periodic dot arrays often exhibit very interesting collective phenomenon. We report a periodic crystal of InCdS pseudo-T5 nanocluster, the largest supertetrahedral cluster found thus far in solid state.