Electron Spin Resonance of Defects Related to Thermal Conductivity in AlN Ceramics

Kai, Ayako; Tomohiro, Daisuke; Kanechika, Yukihiro; Miki, Toshikatsu

doi:10.1143/jjap.47.6394

Cited by 7 publications

(3 citation statements)

References 20 publications

(41 reference statements)

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“…On the other hand, the ESR intensity decreases after O 2 ‐annealed treatment. This result is perfectly consistent with that reported by Kai Ayako et al in AlN ceramics . Therein, the ESR intensity at g = 2.006 decreases with increasing O concentration.…”

Section: Resultssupporting

confidence: 93%

Aluminum‐vacancy‐related dielectric relaxations in AlN ceramics

Wang

2017

J Am Ceram Soc

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The dielectric properties of AlN ceramics were investigated comprehensively in the temperature range from room-temperature to 950 K and frequency range of 10 2 to 5 9 10 6 Hz. The sample exhibits intrinsic dielectric behavior when T < 500 K, showing a flat dielectric permittivity about 10 and an extremely low dielectric loss factor (tand < 2 9 10 À3 ). In the temperature above 500 K, two thermally activated dielectric relaxations related to bulk and interfacial effects were observed. Both relaxations strongly depend on the concentration of oxygen atoms. Our results indicate that the bulk relaxation, occurring in lower temperature range, is caused by aluminum vacancy hopping motion inside grains. The interfacial relaxation, occurring in higher temperature range, is caused by surfacelayer effect due to aluminum vacancies being blocked by sample-electrode contact.

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Section: Resultssupporting

confidence: 93%

Aluminum‐vacancy‐related dielectric relaxations in AlN ceramics

Wang

2017

J Am Ceram Soc

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“…However, C 60 + is unacceptable for the model of Signal A because C 60 + is extremely unstable . A few ESR signals related to O and vacancies in AlN have been reported, but their g ‐values and line widths are different from those of Signal A, e.g., g = 2.004–2.006 and Δ H = 9.0–11.5 mT for an oxygen at a nitrogen site with an adjacent aluminum vacancy . Therefore, Signal A is most likely attributable to dangling bonds with an unpaired electron in amorphous carbon.…”

Section: Resultsmentioning

confidence: 99%

Formation Process of AlN Through Precursors and Its Application to Joining AlN Ceramics

2012

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Formation process of AlN from urea and aluminum chloride hexa-hydrate (N/Al = 60) under nitrogen is investigated. An aluminum hexa-urea complex crystallizes on mixing the two raw materials at room temperature. The complexes react with excess urea and/or its decomposed products, such as biuret above 160°C, and form an amorphous phase containing Al, N, C, and O around 400°C after releasing volatile products. The resultant amorphous phase undergoes changes as the temperature increases, and then crystalline carbon with a fullerene-like XRD pattern forms at 850°C. AlN crystallization follows the decomposition of the fullerene-like crystals. At the AlN precursor stage, a large number of radicals (g = 2.0029 and S = 1/2) are detected by ESR. The radicals are assumed to be due to dangling bonds with an unpaired electron in amorphous carbon. Joining AlN ceramics is conducted using the 850°C product at the AlN precursor stage as the filler material, and is successfully achieved at temperatures above 1000°C. The shear strengths of the joints formed at 1500°C are 88 ± 29 MPa.

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“…SPS is therefore suitable for fabricating transparent ceramics . However, this process introduces defects during sintering in vacuums, and the materials may be contaminated by carbon that is released by the graphite materials used in the sintering chamber …”

Section: Introductionmentioning

confidence: 99%

Electron spin resonance of transparent alumina ceramics fabricated by spark plasma sintering

Kai

Matsuo

2018

J Am Ceram Soc

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Transparent α‐alumina ceramics are fabricated using spark plasma sintering. Paramagnetic defects related to the optical properties of the ceramics have been investigated using electron spin resonance (ESR) analyses. An isotropic ESR signal at g = 2.003 (S = 1/2) with a linewidth of 0.5 mT is formed during sintering. The g = 2.003 signal intensity has a weak correlation with the absorbance in the visible region but does not correlate with the real in‐line transmission (RIT) at 650 nm. An ESR signal with a fine structure attributed to Fe3+ was detected in both the α‐Al2O3 starting powder and the sintered ceramic samples. The degree of c‐axis orientation of the grains has been determined using the Fe3+ signal intensity, which depends on the angle between the directions of the c‐axis and the applied magnetic field. The ESR analysis indicated that the c‐axis tends to be oriented in the direction of the sintering pressure. The degree of c‐axis orientation was found to correlate with the RIT in highly densified ceramics.

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Electron Spin Resonance of Defects Related to Thermal Conductivity in AlN Ceramics

Cited by 7 publications

References 20 publications

Aluminum‐vacancy‐related dielectric relaxations in AlN ceramics

Aluminum‐vacancy‐related dielectric relaxations in AlN ceramics

Formation Process of AlN Through Precursors and Its Application to Joining AlN Ceramics

Electron spin resonance of transparent alumina ceramics fabricated by spark plasma sintering

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