arXiv subjects

Alireza Sepehrinezhad

Publications and source records attributed to Alireza Sepehrinezhad.

4 recordsLinked to original sources

arXiv2026

Ferroelectric Switching in ZnO/Zn1-xMgxO Heterostructures: Atomistic Insights into Interfacial Coupling and Layer Architecture

Ferroelectric switching in heterostructures couples composition, layer topology, temperature, and interfacial boundary conditions. ReaxFF molecular dynamics isolates these variables in ZnO/ Zn1- xMgxO/ZnO and Zn1-xMgxO/ZnO/ Zn1-xMgxO stacks. Within pristine, initially single-domain models, coupling to switchable Zn1-xMgxO reduces the applied field required to reverse ZnO by up to fivefold. Temperature generally lowers the coercive field, whereas Mg concentration produces a nonmonotonic response. At equal ZnO and Zn1-xMgxO (ZMO) proportions, structures with ZnO at the center switch at lower fields than those with ZMO at the center at all four temperatures examined, demonstrating a topology-dependent response. Layer-resolved trajectories reveal topology-dependent switching sequences with direction-dependent redistribution of normal stress near the heterointerfaces, consistent with a stress-assisted cooperative pathway. Limiting MgO-containing structures exhibit sequential multilevel switching or low-polarity trapping, depending on thickness and temperature. Fixed-charge atomistic simulations complement previous continuum descriptions by resolving structural, energetic, and local stress evolution under a common applied field. TEM and STEM-EDS observations provide experimental structural context for the modeled architectures. Together, the results establish layer topology and interfacial mechanical confinement as design variables for wurtzite ferroelectric heterostructures.

cond-mat.mtrl-sci↗

arXiv2026

ReaxKit: A Modular Python Toolkit for Preparing, Parsing, and Analyzing ReaxFF Molecular Dynamics Simulations

Empirical reactive force field (RFF) molecular dynamics enables atomistic simulation of bond breaking, bond formation, charge redistribution, and structural evolution in chemically complex systems. The ReaxFF method is arguably the most popular and transferable of the currently available RFF methods. However, routine use of ReaxFF often requires substantial manual effort to prepare inputs, interpret engine-specific outputs, organize simulation artifacts, and develop custom analysis scripts, limiting reproducibility and scalability. Here, we present ReaxKit, a modular Python toolkit for preparing, parsing, analyzing, and managing ReaxFF molecular dynamics simulations. ReaxKit uses a separation-of-concerns architecture that distinguishes engine-specific input/output handling, canonical domain data models, scientific analysis, workflow orchestration, presentation, storage, and graphical interaction. Engine adapters convert outputs from supported simulation environments into typed, engine-independent data structures, allowing analysis modules to operate independently of native file formats. User requests are executed through consistent command-line, functional Python, and browser-based graphical interfaces, while a dedicated workspace preserves raw data, normalized datasets, analysis settings, results, logs, caches, and provenance information. Representative applications demonstrate the breadth of the toolkit, including automated generation of elastic and equation-of-state training data from Materials Project structures and mechanical properties, characterization of active sites and local structural environments, and execution of simulation campaigns through YAML-defined study workflows. These capabilities show that ReaxKit supports all essential stages of the ReaxFF workflow.

physics.chem-ph↗

arXiv2026

Origin and Reduction of Coercive Fields in ZnO-based Wurtzite Ferroelectrics

Wurtzite ferroelectrics offer a route to semiconductor-compatible non-volatile devices, but their large coercive fields (E$_c$) constrain the operating window between polarization reversal, leakage and dielectric breakdown. Atomically localized and non-classical switching fronts have recently been identified in wurtzite nitrides, yet the microscopic feature that sets the coercive field remains unresolved. Here we use large-scale reactive molecular dynamics, parameterized against first-principles data, to follow field-driven reversal in pristine, Mg-modified and heterostructured ZnO. Reversal proceeds through rugged inversion-boundary filaments in agreement with recent observations in other wurtzite ferroelectrics. We find that the field required for switching is controlled by the advancing filament head, which is a under-coordinated reconstructed inversion-boundary region during the transient switching dynamics with a large field-aligned local polar-order amplitude that is only partially compensated by an oppositely oriented surrounding shell. Controlled strain-only and charge-doping-only perturbations show that charge redistribution lowers the coercive field more effectively than strain because it suppresses this field-setting unscreened local polar order at the filament head, with the combined effect lowering E$_c$ by $\sim$ 50 \%. Layered ZnO/ZnMgO architectures further create buried nucleation sites and shorten filament propagation lengths. These results connect atomistic switching topology to a materials-design principle for substantially reducing coercive fields in ZnO-based wurtzite ferroelectrics.

cond-mat.mtrl-sci↗

arXiv2024

Strain fluctuations unlock ferroelectricity in wurtzites

Ferroelectrics are of practical interest for non-volatile data storage due to their reorientable, crystallographically defined polarization. Yet efforts to integrate conventional ferroelectrics into ultrathin memories have been frustrated by film-thickness limitations, which impede polarization reversal under low applied voltage. Wurtzite materials, including magnesium-substituted zinc oxide (Zn,Mg)O, have been shown to exhibit scalable ferroelectricity as thin films. In this work, we explain the origins of ferroelectricity in (Zn,Mg)O, showing that large strain fluctuations emerge locally in (Zn,Mg)O and can reduce local barriers to ferroelectric switching by more than 40%. We provide concurrent experimental and computational evidence of these effects by demonstrating polarization switching in ZnO/(Zn,Mg)O/ZnO heterostructures featuring built-in interfacial strain gradients. These results open up an avenue to develop scalable ferroelectrics by controlling strain fluctuations atomistically.

cond-mat.mtrl-sci↗