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Reversible thermally stimulated phase transition in amorphous–nanocrystalline β-V2O5 thin films for temperature-sensitive electronics
(2026-01-01)
Tipawan Khlayboonme, S.
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Fungfuang, Natasia
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Kitiwan, Mettaya
V<inf>2</inf>O<inf>5</inf> thin films are significant for next-generation temperature-sensitive electronic devices owing to notable phase stability and reversibility. Optimizing phase characteristics toward reversible low-temperature transitions enhances device performance. In this study, thin films of amorphous–nanocrystalline β-V<inf>2</inf>O<inf>5</inf> were deposited on glass substrates using the inclined magnetron head in radio-frequency magnetron sputtering under an O<inf>2</inf> reactive gas. The effects of thermal stimulation (heating to 400 °C, followed by cooling) were investigated for an as-deposited film prepared at 7.5 % O<inf>2</inf> and for two annealed films deposited at 7.5 % and 10 % O<inf>2.</inf> The annealed films were annealed at 300 °C before thermal stimulation. The films were characterized by X-ray diffractometry (XRD), Auger-electron spectroscopy, field-emission electron microscopy, Van der Pauw and Hall effect measurements, and ultraviolet–visible spectroscopy. The as-deposited film exhibited insulating behavior, whereas the annealed films at 7.5 % and 10 % O<inf>2</inf> demonstrated n-type and p-type conductivities, respectively, accompanied by decreased intensity of the V LMM Auger peak. Before thermal stimulation, the as-deposited film was highly amorphous, whereas the annealed films comprised the β-monoclinic phase. Thermal stimulation caused mixed β-monoclinic and β-tetragonal symmetries for all films and induced significant changes in surface morphology, except for the annealed film at 7.5 % O<inf>2</inf>. Variations in carrier density and bandgap energy indicated that thermal energy promoted oxygen vacancies but reduced vanadium vacancies in the film structure. In situ XRD analysis demonstrated the phase stability and reversible formation of the nanocrystalline β-monoclinic phase, revealing potential for thermally responsive applications requiring repeatable phase behavior.
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Effects of substrate rotational speed and phase transition on β-V2O5 for temperature-sensitive thin films
(2025-12-01)
Fungfuang, Natasia
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Khlayboonme, S. Tipawan
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Kitiwan, Mettaya
The phase stability and reversibility of V<inf>2</inf>O<inf>5</inf> are crucial for smart, contactless optical thermal sensors. Controlling phase characteristics optimizes device performance, particularly by achieving lower phase-transition temperatures with reversible properties. This study examines the effects of substrate rotational speed on the phase content and homogeneity of V<inf>2</inf>O<inf>5</inf> thin films deposited via radiofrequency magnetron sputtering using an inclined magnetron head and an O<inf>2</inf>-reactive process. Characterized using X-ray diffraction, electron microscopy, Hall effect measurements, and ultraviolet–visible spectroscopy, the films exhibited a mixture of β-monoclinic and β-tetragonal phases. Increasing the substrate rotational speed from 0 to 40 rpm increased the film thickness from 125 to 220 nm but reduced the crystallite size from 16.8 to 7.9 nm for the β-monoclinic phase. The direct bandgap energy decreased from 3.582 to 2.56 eV, and the electron density decreased from 2.92 × 1018 to 5.2 × 1017 cm−3, suggesting suppressed depletion of vanadyl oxygen in the film structure. Optical analysis revealed that the dispersive energy for the β-monoclinic phase increased from 24.7 to 30.3 eV as the rotational speed increased—attributed to stronger polarization due to lattice vibrations. The responses of the annealed and as-deposited films to thermally induced stimuli were investigated. During cooling to 100 °C, the β-tetragonal phase content continued to increase, whereas the β-monoclinic phase content decreased and appeared to revert to levels observed before heating. This result revealed a reversible β-monoclinic phase transformation during cooling, indicating the potential of amorphous β-monoclinic V<inf>2</inf>O<inf>5</inf> films for chromic and temperature-sensitive sensors with repeatable performance.
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Thermally induced phase transition and dielectric relaxation in lead-free BaTi0.94Sn0.06O3 Ceramics: Insights from in-situ XRD and XAS
(2025-11-01)
Sukkha, Usa
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Chanlek, Narong
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Kidkhunthod, Pinit
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Kolodiazhnyi, Taras
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Vittayakorn, Wanwilai
Lead-free BaTi<inf>0.94</inf>Sn<inf>0.06</inf>O<inf>3</inf> (BTS) ceramics were synthesized using the conventional solid-state reaction method to investigate thermally induced phase transitions and dielectric relaxation phenomena. A combination of in-situ X-ray Diffraction (XRD) and in-situ Synchrotron X-ray Absorption Spectroscopy (XAS) was employed to examine phase transitions across the temperature range of 200–400 K. The results reveal sequential phase transitions: rhombohedral-orthorhombic (R + O) at 200 K, orthorhombic (O) at 250–300 K, tetragonal (T) at 325–359 K, and tetragonal-cubic (T + C) at 373–400 K. Dielectric measurements highlight an anomalous relaxation behavior at 70–160 K, attributed to domain wall freezing. This phenomenon follows Vogel-Fulcher behavior, with an activation energy of 14 meV, a freezing temperature of 82 K, and an attempt frequency of 4.7 × 106 Hz. X-ray Photoelectron Spectroscopy (XPS) analysis reveals oxygen deficiency on the surface of the BTS ceramic, resulting in the coexistence of Ti3+/Ti4+ and Sn2+/Sn4+ oxidation states. These defects significantly influence the dielectric and phase transition properties. This study provides comprehensive insights into the interplay between local structural changes and phase transition mechanisms in BTS ceramics. By employing a multi-technique approach, it advances the understanding of dielectric and ferroelectric behaviors, positioning BTS ceramics as promising candidates for lead-free dielectric and ferroelectric device applications.
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Pressure-induced phase transition and indirect band gap semiconductor in ZnSnN2: First Principles Calculation
(2025-01-01)
Sailuam, Wutthigrai
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Fongkaew, Ittipon
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Kongnok, Thanundon
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Kotmool, Komsilp
In this study, we investigate the phase transition of ZnSnN<inf>2</inf> from Pna2<inf>1</inf> to Pmnb using Density Functional Theory (DFT) across a pressure range of 0–70 GPa. Our results show the enthalpy intersection of the Pna2<inf>1</inf> and Pmnb phases at 19.28 GPa, indicating a phase transition from Pna2<inf>1</inf> to Pmnb ZnSnN<inf>2</inf>. The decrease in H<inf>v</inf> of the Pna2<inf>1</inf> phase under pressure before the phase transition is attributed to the reduction of the G and weakening covalent bond of Sn–N pair. The new Pmnb phase exhibits an increased Vickers hardness, Debye temperatures, and brittleness. Moreover, the band gap is an indirect band gap of 1.41 eV due to a rearrangement of lower energy levels for Sn s and p states in conduction band minimum (CMB) and N s and p states in valence band maximum (VBM) at Γ-point. These characteristics make The Pmnb phase promising candidates for applications were longer carrier lifetimes are needed. The mechanical properties, dynamical behavior, and electron localization functions (ELFs) have been investigated and discussed.
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Investigating the phase transition and properties of CaSiN2 under pressure based on first-principles calculations
(2023-12-01)
Meethan, Weerachon
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Kongnok, Thanundon
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Fongkaew, Ittipon
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Bootchanont, Atipong
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Saisopa, Thanit
In this study, we apply first-principles calculations to examine the pressure-induced phase transformation of CaSiN<inf>2</inf> in a range of pressure of 0–100 GPa. Its pressure-induced transitions at 1.3 GPa, 15.3 GPa, and 55.8 GPa followed the order of α- CaSiN<inf>2</inf> → β- CaSiN<inf>2</inf> → α- CaSiN<inf>2</inf> → γ- CaSiN<inf>2</inf>, for α- CaSiN<inf>2</inf> → β- CaSiN<inf>2</inf>, β- CaSiN<inf>2</inf> → α- CaSiN<inf>2</inf>, and α- CaSiN<inf>2</inf> → γ- CaSiN<inf>2</inf>, respectively. The stability of the phases of CaSiN<inf>2</inf> was confirmed based on calculations of the Born criterion of elastic stability. Its behavior transitioned in the sequence of brittle (0–1.3 GPa) → ductile (1.3–55.8 GPa) → brittle (55.8–100 GPa). The structure of its projected orbital band reflected insulating behavior by CaSiN<inf>2</inf> under a range of pressure of 0–55.8 GPa with a direct band gap, which transformed into metallic behavior by the γ- CaSiN<inf>2</inf> phase under pressures higher than 55.8 GPa, due to a shift in energy to higher levels around the Γ point of the N p orbitals and Si p orbitals. The Si-N bonds in CaSiN<inf>2</inf> were found to be covalent, while ionic bonding dominated the Ca-Si and Ca-N bonds in the range of pressure of 0–100 GPa. We also investigate and discuss its mechanical properties, Vickers hardness (H<inf>v</inf>), average sound velocity v<inf>m,</inf> and Debye temperature (θ<inf>D</inf>).
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Preparation of BST Powders and Ceramics via a Hybrid Method
(2023-01-01)
Klaytae, Thanawat
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Vittayakorn, Naratip
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Sumang, Rattiphorn
Barium strontium titanate (Ba<inf>0.8</inf>Sr<inf>0.2</inf>TiO<inf>3</inf>; BST) ceramics, were prepared by the hybrid method between Solid-state reaction (SSR) and Sol-gel methods (SG) in a ratio of 1:0.1–1:0.5. The BST powder was successfully calcined at 850 °C for 2 h. This temperature is much lower than the calcination temperatures of the SSR method. The BST ceramics were sintered between 1150 and 1450 °C. All samples showed the pure perovskite structure corresponding to JCPDS no. 34-0411. The optimum sintering temperature was observed from the samples sintered at 1450 °C for 4 h, indicating a density of 5.26 g/cm3, dielectric constant of 7018, and ferroelectric properties: (P <inf>max</inf> = 13.8 μC/cm2, P <inf>r</inf> = 2.5 μC/cm2 and E <inf>c</inf> = 2.3 kV/cm at 30 kV/cm).
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Transition between monoclinic and tetragonal β phases induced by reactive oxygen gas in RF-sputtered V2O5 thin films
(2022-11-01)
Khlayboonme, S. Tipawan
Thin films of V<inf>2</inf>O<inf>5</inf> are promising materials for applications in chromogenic devices, such as gas sensors and contactless optical thermal sensors. Therefore, controlling the formation of the various phases of V<inf>2</inf>O<inf>5</inf> is important. The device performance, in relation to satisfactory coloration efficiency and fast response, strongly depends on the characteristics of the phase incorporated in the film structure. To better understand the phase formation in these films, thin films of V<inf>2</inf>O<inf>5</inf> were deposited by RF magnetron sputtering using an O<inf>2</inf>-reaction technique from a metallic V target, and the influence of RF power and O<inf>2</inf> levels on the transition between the β-monoclinic and β-tetragonal phase structures was investigated by X-ray diffractometer. The films were also evaluated using Auger-electron, Raman-, and UV-vis spectrometers to determine their composition, chemical, and electronic properties to assess the effects of the two sputtering parameters. The mechanism underlying the development of film properties is related to the plasma characteristics and species observed by optical emission spectroscopy. Increasing the RF power resulted in a higher phase content of the β-monoclinic and α-orthorhombic phase, whereas an increasing the oxygen levels induced a phase transition towards the β-tetragonal phase of V<inf>2</inf>O<inf>5</inf>. Films with different phase contents exhibited different optical energy bandgaps. Plasma diagnostics showed that increasing the RF power increased the thickness of plasma sheaths on the target surface. The thinner sheath on the target surface further increased the β-tetragonal phase content. The variation between β-monoclinic and β-tetragonal phase content was expected because of the bombardment of energetic O− ions that were accelerated from the plasma sheath toward the growth surface. A deeper understanding of the transition between β phases in V<inf>2</inf>O<inf>5</inf> films can enable better phase control, which can improve film application towards various sensing devices, particularly chromic- or temperature-sensors.
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Effect of pressure on structural and elastic properties of SnSe: First-principles calculations
(2022-02-01)
Phacheerak, Kanoknan
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Thanomngam, Pitiporn
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Limpijumnong, Sukit
Selected structural and elastic properties of an orthorhombic SnSe at an ambient pressure and under high pressures were investigated using first-principles calculations. At ambient pressure, the calculated structural parameters and elastic constants show a good agreement with previously reported values. Effects of pressure on structural and elastic properties were presented and discussed in detail. Moreover, the pressure dependence of selected structural and elastic properties, which relate to phase transition from an orthorhombic phase to the high-pressure phase, was analyzed. We suggested that the phase transition is related to the compression along the c- and b-axis which correspond to C<inf>33</inf> and C<inf>22,</inf> respectively.
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Fe-doped effects on phase transition and electronic structure of CeO2 under compressed conditions from ab initio calculations
(2021-10-01)
Sathupun, Karnchana
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Kotmool, Komsilp
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Tsuppayakorn-aek, Prutthipong
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Pluengphon, Prayoonsak
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Majumdar, Arnab
Ab initio study of high-pressure phase transition and electronic structure of Fe-doped CeO<inf>2</inf> with Fe concentrations of 3.125, 6.25, and 12.5 at% has been reported. At a constant-pressure consideration, the lattice constants and the volume of the supercell were decreased with an increasing concentration of Fe. The average bond length of Fe–O is lower than that of Ce–O. As a result, Fe doping induces the reduced volume of the cell, which is in good agreement with previous experiments. At high pressure (~ 30 GPa), it was found that the transition pressure from the fluorite to the cotunnite orthorhombic phase decreases at a higher concentration of Fe, indicating that the formation energy of the compound is induced by Fe-doping. Furthermore, compression leads to interesting electronic properties too. Under higher pressures, the bandgap increases in the cubic structure under compression and then suddenly plummets after the transition to the orthorhombic phase. The 3d states of Fe mainly induced the impurity states in the bandgap. In both the undoped and Fe-doped systems, the bandgap increased in the cubic phase at high pressure, while the gap and p-d hybridization decrease in the orthorhombic phase.
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High piezoelectric response in the new coexistent phase boundary of 0.87BaTiO3-(0.13-x)BaZrO3-xCaTiO3
(2015-12-05)
Sutapun, Manoon
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Vittayakorn, Wanwilai
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Muanghlua, Rangson
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Vittayakorn, Naratip
An investigation of the coexistent ferroelectric phase was carried out on the ternary system of 0.87BaTiO<inf>3</inf>-(0.13-x)BaZrO<inf>3</inf>-xCaTiO<inf>3</inf> [abbreviated as BT-BZ-xCT (where 0.00≤x≤0.13)]. Temperature-, frequency-dependent dielectric data, electric field-dependent strain and polarization as a function of composition are presented in order to understand the relationships of structure-properties and find the high piezoelectric response in this system. Results showed that ceramics in the composition range of 0.00≤x<0.04 were of a rhombohedral structure and transformed into a tetragonal structure at x>0.06. The multiphase coexistence of the rhombohedral and tetragonal phase in this system was identified at x=0.06. A large, virtually hysteresis-free electric field induced strain of 0.23% was achieved with the composition, x=0.06, at 40kV/cm on the boundary between rhombohedral and tetragonal phase. This relates to an extraordinarily high and normalized piezoelectric coefficient (S<inf>max</inf>/E<inf>max</inf>) of 1280pm/V, which was reached at a low electric field applied at 10kV/mm. These results indicated that a high piezoelectric response may stem primarily from the rhombohedral-tetragonal phase boundary, due to greater lattice softening and reduced energy barriers for polarized rotation.

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