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Post-annealing effects on (00l) texture, Cl/Se ratio, and electrical and glass-like thermal transport in Bi₄O₄SeCl₂
(2026-04-25)
Somdock, Nuttakrit
;
Theekhasuk, Nattharika
;
Voraud, Athorn
;
Limsuwan, Pichet
;
Naemchanthara, Kittisakchai
Bi₄O₄SeCl₂ is a heteroanionic layered material with intrinsically low lattice thermal conductivity and anisotropic charge transport. In this work, the effects of post-annealing temperature on the crystallographic texture, anion chemistry, defect evolution, and transport properties of Bi₄O₄SeCl₂ were systematically investigated. Polycrystalline Bi₄O₄SeCl₂, synthesized by solid-state reaction combined with high-energy ball milling, was post-annealed at 400–700 °C. X-ray diffraction and electron microscopy revealed that post-annealing eliminated the residual BiOCl precursor phase, enhanced the (00 l) preferred orientation, and promoted grain growth up to 600 °C, followed by partial texture degradation at 700 °C due to recrystallization. Energy-dispersive spectroscopy showed progressive Se and Cl volatilization during annealing, leading to an increased Cl/Se ratio. The carrier mobility and electrical conductivity reached maximum values at 600 °C, consistent with improved texture and layered-domain connectivity. Thermal transport remained lattice-dominated and only weakly temperature-dependent. The phonon mean free path, estimated using kinetic theory, was in the sub-nanometer range (∼0.25–0.57 nm), comparable to the interatomic spacing, indicating glass-like phonon transport. Representative HRTEM observations also revealed dislocation-related lattice defects and locally distorted regions, suggesting that vacancy disorder and local strain fields may provide additional phonon scattering. These results demonstrate that post-annealing optimizes electrical transport through phase purification, texture development, and defect-mediated carrier regulation, while the lattice thermal conductivity remains fundamentally limited by intrinsic glass-like phonon transport in Bi₄O₄SeCl₂.
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Improvement of structural, morphological and mechanical properties of CrNx sputtered thin films by vacuum annealing process
(2017-01-01)
Nualkham, Intira
;
Sakdanuphab, Rachsak
;
Sakulkalavek, Aparporn
In this study, CrNx thin films were prepared on 304 stainless steel substrate by DC reactive magnetron sputtering technique. Different N2 gas partial pressure from 10 to 30% was employed in the sputtering process while sputtering power, sputtering pressure and total film thickness were kept constant. In order to improve structural, morphological, and mechanical properties, vacuum annealing process was adopted on the CrNx thin films at the temperature of 400 °C. The standard characterization techniques such as X-ray diffraction, scanning electron microscope, atomic force microscope and hardness (load force of HV0.1) were used to reveal the properties of as-deposited and annealing films. The as-deposited films show two-phase crystal structure of Cr2N and CrN depending on N2 gas partial pressure. After the annealing process, the films effectively enhance the crystal structure and found the phases change from Cr2N to CrN for the film deposited at low N2 partial pressure. The surface roughness of the films was between 5 - 20 nm, and as expected the annealing films shows smoother surface than the as-deposited films. Hardness of the CrNx films is in the range of 7 to 10 GPa. The mechanism of improvement in structural and mechanical properties of annealing films is introduced based on strain relaxation.

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