arXiv subjects

Ali Sarikhani

Publications and source records attributed to Ali Sarikhani.

4 recordsLinked to original sources

arXiv2026

Grain Growth Kinetics in (Cr,Mo,Ta,V,W)C1-{\delta} High-Entropy Carbide Ceramics

Understanding grain-boundary mobility during spark plasma sintering can enable microstructure control in high-entropy carbides, yet quantitative grain-growth kinetics remain scarce. In this work, grain growth kinetics and densification behavior were investigated for single-phase fully dense (Cr,Mo,Ta,V,W)C1-{\delta} high-entropy carbide ceramics. Specimens were densified by spark plasma sintering for a constant dwell time of 10 min at temperatures between 1750 {\deg}C and 1950 {\deg}C to isolate the role of temperature on microstructural evolution. Increasing sintering temperature produced grain growth and increased lattice parameter, while maintaining a single-phase rock salt structure. Elemental mapping showed a progressive reduction of Ta segregation with increasing sintering temperature, suggesting enhanced chemical homogenization at elevated temperatures. Grain growth kinetics were analyzed using a normal grain growth model with an assumed growth exponent of n=3, physically reasonable for grain-boundary-controlled growth influenced by solute and vacancy pinning. Arrhenius analysis of the growth factor yielded an apparent activation energy of approximately 620 kJ mol-1, comparable to diffusion-controlled processes in refractory transition-metal carbides. Densification curves revealed rapid consolidation prior to reaching the peak temperature followed by temperature-dominated grain coarsening. These results establish quantitative relationships between densification temperature, grain growth, and diffusion kinetics in a carbide system, providing insight into the microstructural stability of high-entropy, ultra-high-temperature carbide ceramics.

cond-mat.mtrl-sci↗

arXiv2025

Thermal and Electrical Properties of (Cr,Mo,Ta,V,W)C High-Entropy Carbide Ceramics

The synthesis and characterization, along with the resulting properties, of fully dense $(\mathrm{Cr, Mo, Ta, V, W})\mathrm{C}$ high-entropy carbide ceramics were studied. The ceramics were synthesized from metal oxide and carbon powders by carbothermal reduction, followed by spark plasma sintering at various temperatures for densification. Increasing the densification temperature resulted in grain growth and an increase in the lattice parameter. Thermal diffusivity increased linearly with testing temperature, resulting in thermal conductivity values ranging from approximately $7~\mathrm{W\,m^{-1}\,K^{-1}}$ at room temperature to $12~\mathrm{W\,m^{-1}\,K^{-1}}$ at $200~^\circ\mathrm{C}$. Measured heat capacity values matched theoretical estimates made using the Neumann--Kopp rule. Room-temperature electrical resistivity decreased from $137$ to $120~\mu\Omega\cdot\mathrm{cm}$ as the excess carbon decreased from $5.4$ to $0.1~\mathrm{vol\%}$, suggesting an enhanced electronic contribution to thermal conductivity as excess carbon decreased. All specimens exhibited a Vickers hardness of approximately $29~\mathrm{GPa}$ under a $0.49~\mathrm{N}$ load. These results underscore the tunability of this high-entropy carbide system.

cond-mat.mtrl-sci↗

arXiv2025

Observation of Anomalous Hall Effect in Bulk Single Crystals of n-type Cr-doped Sb$_{2}$Te$_{3}$ Magnetic Topological Insulator

The exploration of topological Dirac surface states is significant in the realms of condensed matter physics and future technological innovations. Among the materials garnering attention is Sb$_{2}$Te$_{3}$, a compound that theoretically exhibits topological insulating properties. However, its inherent p-type nature prevents the direct experimental verification of its Dirac surface state due to the Fermi level alignment with the valence band. In this study, by doping Cr atoms into Sb$_{2}$Te$_{3}$, n-type behavior is observed in the Hall resistance measurements. Remarkably, the Cr-doped Sb$_{2}$Te$_{3}$ not only shows ferromagnetism with a high transition temperature of approximately 170 K but also exhibits an anomalous Hall effect (AHE). The Cr doping also allows for a controlled method for Fermi level tuning into the band gap. These properties spotlight its potential as an n-type magnetic topological insulator (MTI) as well as a material candidate for the quantum anomalous Hall effect (QAHE), opening new avenues for applications in spintronics and quantum devices.

cond-mat.mtrl-sci↗

arXiv2024

Emergent Spin Fluctuation and Structural Metastability in Self-Intercalated Cr$_{1+x}$Te$_2$ Compounds

Intercalated van der Waals (vdW) magnetic materials host unique magnetic properties due to the interplay of competing interlayer and intralayer exchange couplings, which depend on the intercalant concentration within the van der Waals gaps. Magnetic vdW compound chromium telluride, Cr$_{1+x}$Te$_2$, has demonstrated rich magnetic phases at various Cr concentrations, such as the coexistence of ferromagnetic and antiferromagnetic phases in Cr$_{1.25}$Te$_2$ (equivalently, Cr$_{5}$Te$_8$). The compound is induced by intercalating 0.25 Cr atom per unit cell within the van der Waals gaps of CrTe$_2$. In this work, we report a notably increased Curie Temperature and an emergent in-plane spin fluctuation by slightly reducing the concentration of Cr intercalants in Cr$_{1.25}$Te$_2$. Moreover, the intercalated Cr atoms form a metastable 2$\times$2 supercell structure that can be manipulated by electron beam irradiation. This work offers a promising approach to tuning magnetic and structural properties by adjusting the concentration of intercalated magnetic atoms.

cond-mat.mtrl-sci↗