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Tetsuya SENDA, Richard C. Bradt
1991 Volume 99 Issue 1153 Pages
727-731
Published: September 01, 1991
Released on J-STAGE: August 06, 2010
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Crystallographic twins which form in sintered ZnO varistor ceramics with Sb
2O
3 additions are considered in terms of established crystallographic twinning mechanisms. Possible twin origins from either phase transformations or a result of deformation are both rejected. It is concluded that the ZnO twins are growth twins which nucleate in the early stages of sintering and grain growth of the ceramic powder compact. Consideration of the oxygen anion stacking layer sequences in the hexagonal ZnO wurtzite structure and the cubic Zn
7Sb
2O
12 spinel structure suggests that the nuclei for the twins may form as embryos consisting of a faulted region of the spinel-oxygen anion layer stacking sequence. The faulted layer sequence is created by the presence of the antimony oxide and its reaction with the ZnO. The fact that the wurtzite structure is polar and the ZnO twins are inversion twins explains why there is only a single twin per grain, as multiple twins would result in the unfavorable tail-to-tail structural configuration.
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Akira KANI, Yoshihiro TEJIMA, Hiroshi HIRABAYASHI, Akira URA
1991 Volume 99 Issue 1153 Pages
732-736
Published: September 01, 1991
Released on J-STAGE: August 06, 2010
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Chemical reaction between SiC ceramics and solid metals has been used for making grooves on the sliding face of SiC ceramics. The grooving process was carried out by the procedure in which a stainless steel foil with exactly the same shape as the groove pattern was placed on the surface of the SiC ceramics, and a fragile product obtained by the chemical interaction at high temperature was removed. To accomplish the grooving process, the grooved face should be free from cracks and smooth. When the cracks were not generated on the SiC face, the cracks appeared on the stainless steel foil by the deterioration of the metal phase, i.e, the formation of fragile materials such as Fe
5Si
3, Cr
23C
6 and graphite during the reaction. The crack generation in SiC tended to initiate at lower reaction temperature with thick foils. The actual grooving process was considered to be accomplished by this interaction method.
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Kouichi YASUDA, Yohtaro MATSUO, Shiushichi KIMURA, Tsutomu MORI
1991 Volume 99 Issue 1153 Pages
737-744
Published: September 01, 1991
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Effects of microstructure on fracture toughness were investigated. Using the equivalent inclusion method, the change in Gibbs' free energy was caluculated for a relatively large body containing a main crack and many spherical micropores (or penny-shaped microcracks). Applying the Griffith's fracture criteria to the model, the effects of micropores (or microcracks) on fracture toughness were formulated. The fracture toughness decreased with the increase in volume fraction of micropores (or microcracks). Furthermore, the fracture toughness of a body with microcracks, depended on the volume fraction more remarkably than that with micropores. The tendencies of the experimental results reported previously, were explained by this theoretical analysis.
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Taketoshi FUJITA, Ken-ichiro SUGIMORI, Hiromoto NAKAZAWA
1991 Volume 99 Issue 1153 Pages
745-750
Published: September 01, 1991
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Exchange of fluorine for hydroxide ions in synthetic fluor-phlogopite (KMg
3AlSi
3O
10F
2) was studied in hydrothermal solutions of various concentrations of NaOH and LiOH. The pressure applied was fixed at 100MPa, temperatures were 300°, 450° and 600°C, and the experimental duration was 7 days. The dependence of the alkali species on the exchange efficiency was studied in comparison with that of KOH, as reported previously. The conversion rate at 600°C in the different alkaline solutions was higher in the order of NaOH>KOH>LiOH. In the case of NaOH, conversion of 90% or more was attained, and the crystallinity of the mica produced was higher than that in other alkaline solutions. Occasionally, euhedral crystals of about 0.5mm were obtained. Several secondary phases were found in some conditions: (1) sodium phlogopite-like phase in NaOH solution at low temperature (<500°C) and low concentration (5M/dm
3<), (2) 1:1 phases, probably halloysite (<500°C) and serpentine (>500°C), in concentrated NaOH solution (=10M), (3) Mg(OH)
2 (<500°C) and an unidentified phase (>500°C) in LiOH solution. The solubility of fluorine in the OH-rich phlogopite decreased with increasing temperature over 500°C in NaOH and LiOH solutions. This substitution behavior is in contrast with that found in KOH solutions, and is explained by the coexistence of the secondary phases described above.
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Noboru HASHIMOTO, Hiroyoshi YODEN, Kazuo NOMURA, Shigehito DEKI
1991 Volume 99 Issue 1153 Pages
751-756
Published: September 01, 1991
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Effect of carbon on the synthesis of AlN powder from aluminum polynuclear complexes was investigated. Aqueous solutions of basic aluminum chloride and glucose were used as starting materials. C/Al molar ratio was varied to investigate the effect on the reactivity of nitridation and particle size of synthesized AlN powder. The structure of the solution was investigated by
27Al and
13C-NMR spectroscopy. It was found that reactivity of nitridation took a maximum value at 1.8-2.0 of C/Al molar ratio and thereafter decreased gradually. This indicates that excess carbon inhibits the transportation of reaction gases at a gap among the particles. In this reaction system, C/Al molar ratio for the maximum reactivity nitridation is much smaller than that in the alumina-carbon black mixture system. Furthermore, this value is closer to the theoretical value for a complete nitridation reaction. These results suggest that carbon in our system is distributed more homogeneously than that in the alumina-carbon black mixture system. The particle size of the synthesized AlN powder decreases with increasing C/Al molar ratio. Obviously, carbon has a strong effect on the particle size of γ-alumina, which is formed as an intermediate in the nitridation process, and prevents the grain growth of the synthesized AlN particles. It was found that aluminum polynuclear complex and glucose formed a precursor in the solution.
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Katsuyoshi SHIMOKAWA, Itsuma SEKIGUCHI, Yoshikazu SUZUKI, Katsumasa YA ...
1991 Volume 99 Issue 1153 Pages
757-762
Published: September 01, 1991
Released on J-STAGE: August 06, 2010
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Ceramic fibers consisted of three elements, Si, O and C, were synthesized from carbide obtained from a natural organic material; rice husk. TEM was used to analyze the synthesized fibers. One fiber synthesized in N
2 consisted of a two-layered structure of laminate covering a center core fiber. Another fiber synthesized in a mixture of N
2 and H
2 consisted of a three-layered structure of two laminates covering a core fiber. The fiber core was found to be crystallized and covered with an amorphous material, which contained concentrated oxygen. The core fiber did not dissolve in strong acid solutions and was very reactive with oxygen. From the results of X-ray diffraction and solubility in acid solution, it was found that the inside laminate from the surface layer to the core of the fiber formed a structure which was crystallized weakly into β-SiC, and Si-O-C. This study clearly shows that fiber synthesized from rice husk formed a continuous structure with varying concentration of oxygen and carbon-bound silicon; that is a new material with gradient structure.
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Toshinori KOKUBU, Tetsuo MATSUYAMA, Masayuki YAMANE
1991 Volume 99 Issue 1153 Pages
763-767
Published: September 01, 1991
Released on J-STAGE: August 06, 2010
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Colored TiO
2-SiO
2 porous glass-ceramics, TPGC, which incorporated transition metals, were prepared and their uranium adsorption capacities from an experimental uranium solution and sea water have been investigated. The glass-ceramics were heat-treated to give a crystalline phase of rutile through phase separation. The surface of micropore of TPGC was covered with hydroxyl groups, Ti-OH or Si-OH. The mean pore diameter of TPGC was about 100Å, the pore volume was about 0.3-0.4cc·g
-1, and the specific surface area was in the range between 100 and 150m
2·g
-1. The uranium adsorption capacity of Co-incorporated TPGC was estimated to be 100mg-U·g-TPGC
-1. The adsorption quantity under 100ml·h
-1 liquid flow resulted in 72.5mg-U·g-TPGC
-1 at 30°C and pH 6. The high uranium adsorption capacity shows the potential applicability of TPGC in the recovery of uranium ion from a waste solution.
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Toshio SHIMOO
1991 Volume 99 Issue 1153 Pages
768-773
Published: September 01, 1991
Released on J-STAGE: August 06, 2010
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Three kinds of SiC powders were synthesized by the carbothermic reduction of SiO
2 at 1973K in an Ar atmosphere from reagent graphite, electrode graphite and carbon black. The oxidation rates of free carbon and SiC component in these powders were measured in an O
2 gas stream at temperatures from 923 to 1573K by the thermogravimetric analysis and the determination of CO
2 evolved. As the powders synthesized from the reagent graphite and carbon black were surrounded continuously by SiC layer, the free carbon could not be removed by oxidation. The free carbon in the powder synthesized from the electrode graphite was partly removed. The activation energy for the oxidation of free carbon was 173kJ/mol. This oxidation was controlled by a chemical process. The oxidation of SiC component in the powder initiated at 1073K. The oxidation rate was significantly dependent on surface state of the powder. Jander's rate equation was applicable to the oxidation rate of SiC. The activation energy varied from 217 to 283kJ/mol. The oxidation of SiC is probably controlled by the diffusion of O
2- ion in the SiO
2 film formed around the SiC particles.
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Yuichi DESHIMARU, Tetsuya OTANI, Youichi SHIMIZU, Norio MIURA, Noboru ...
1991 Volume 99 Issue 1153 Pages
774-779
Published: September 01, 1991
Released on J-STAGE: August 06, 2010
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Oxygen sorption-desorption behavior as well as superconducting properties were examined for four Bi-based oxides (2212 phase, Bi
2-xPb
xSr
2-yCa
1+yCu
2O
8+δ: (
x, y)=(0, 0), (0, 0.8), (0.2, 0), (0.2, 0.8)). Temperature-Programmed-Desorption (TPD) mesurements revealed that reversible sorption and desorption of small amounts of oxygen (ca. 2-3×10
-5mol/g) were observed for all the samples below 600°C. The
Tc and lattice parameters (
c) were found to change reversibly with the oxygen content. The oxygen content dependence of
Tc for the
y=0 sample was quite different from that for
y=0.8, i.e.,
Tc increased with decreasing oxygen content in the former, while in the latter
Tc decreased. On the other hand, the oxygen content dependence for
x=0 was similar to that for
x=0.2. The optimum oxygen content (hole concentration) for the highest
Tc in Bi
2Sr
1.2Ca
1.8Cu
2O
8+δ was confirmed to be δ=0.15.
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Tamotsu YASUE, Yoshihiro SHIOYA, Yasuo ARAI
1991 Volume 99 Issue 1153 Pages
780-787
Published: September 01, 1991
Released on J-STAGE: August 06, 2010
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The preparation of glasses, fibres and ultra-fine powders for fine-ceramic materials by the alkoxide method has recently attracted special interest. Tobermorite is generally synthesized by hydrothermal reaction under saturated steam pressure of 10kgf/cm
2 above 180°C in unhomogeneous suspension of CaO(solid)-SiO
2(solid)-H
2O (liquid) system. A study was made to investigate the synthesis of Al
3+-substituted tobermorite at a low temperature (95°C) under atmospheric pressure by using homogeneous mixed solutions of the CaCl
2-Si(OC
2H
5)
4-AlCl
3-C
2H
5OH-H
2O system. The thermal behavior and cation exchange for the Al
3+-substituted tobermorite were carried out by means of X-ray diffraction, thermal analysis (TG-DTA), infrared spectroscopy and chemical analysis. The procedure for the synthesis of Al
3+-substituted tobermorite consisted of deposition of a CSH gel from homogeneous mixed solutions (Ca/Si atomic ratio: 1.0, Al/(Al+Si) atomic ratio: 0.03-0.20) by adding KOH solution and the crystallization of the gel by aging at 95°C under atmospheric pressure for 5 days. A basal spacing due to (002) plane in tobermorite was affected by the Al/(Al+Si) atomic ratio; 10.7Å below the atomic ratio of 0.03 and 11.3Å in the atomic ratio of 0.05-0.20. The crystallization of Al
3+-substituted tobermorite was much accelerated in the range of the Al/(Al+Si) atomic ratio of 0.05-0.10 but converted to the CSH gel over the atomic ratio of 0.20. A basal spacing expanded with increasing Al
3+ substituted for Si
4+ in silicate ion chains of tobermorite dependent on the substitution of greater Al
3+ than Si
4+ in size and the limitation for this substitution were approximately 18% as Al
3+. Consequently, Al
3+-substituted tobermorite included much K
+ which was supplied to neutralize the electric charge happened by the substitution. The capacity of cation exchange for K
+→←Na
+ of Al
3+-substituted tobermorite increased with increasing amount of substituted Al
3+. The maximum capacity was 80-90meq/100g. Even in the case of the CSH gel, the capacity indicated the same values but in the exchange capacity per unit-surface, the former showed higher value than the latter.
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Naoki WAKIYA, Hiroyasu SUMINO, Kazuo SHINOZAKI, Nobuyasu MIZUTANI
1991 Volume 99 Issue 1153 Pages
788-792
Published: September 01, 1991
Released on J-STAGE: August 06, 2010
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I (current)-
V (voltage) characteristics of single grain boundaries in ZnO varistor were directly measured by D. C. four-point probe method using a constructed instrument. The
I-V characteristics of single grain boundaries were different at each grain boundary and classified into three patterns. The resistance of the grain boundary phase seemed to affect the
I-V characteristics of the grain boundary. Non-linear coefficients of single grain boundaries were in the range of 2 to 100 and their average value was 14.8, in good agreement with that of the sintered body. The breakdown voltage of single grain boundaries also varied widely between 1.5-5V with an average value of 3.3V. The breakdown voltage of a single grain boundary calculated from that of the sintered body was 1.88V. One of the factors affecting the difference between the measured and calculated value of the breakdown voltage was considered to be the difference in the measuring current density.
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Hirohiko MURAKAMI, Osamu OKAMURA, Tamotsu NODA, Yuh SHIOHARA, Shoji TA ...
1991 Volume 99 Issue 1153 Pages
793-797
Published: September 01, 1991
Released on J-STAGE: August 06, 2010
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Superconducting thick films 1mm wide and 1-100μm thick were prepared on Ag substrates by gas deposition using a YBa
2Cu
3O
7-x (123) ultrafine powder. After heat treatment at 850°C for 10h in O
2 atmosphere, a 123 thick film (1μm) with random grain orientation had a
Jc of 2300A/cm
2 at 77K. The effects of Ag substrate and the depression of melting point of 123 ultrafine powder were discussed from a thermodynamic point of view.
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Hiroshi SHIGA, Mohamed G. M. U. ISMAIL, Keiichi KATAYAMA
1991 Volume 99 Issue 1153 Pages
798-802
Published: September 01, 1991
Released on J-STAGE: August 06, 2010
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Mullite/ZrO
2 composite ceramics were fabricated from sol-gel derived powders. The effects of ZrO
2 content and firing temperature on the densification and microstructure development have been investigated by means of SEM, TEM and XRD. It was clarified that the 5 to 25vol% addition of ZrO
2 to mullite improved the sinter-ability. The effect is more striking in the composites containing 10 or 15vol% ZrO
2. The growth of mullite grains was inhibited by dispersing ZrO
2 particles. The effects were, especially, most predominant in the composite containing 15vol% ZrO
2. However, in composites fired at 1650°C and above, remarkable grain growth was observed, and needle-like mullite grains having Al-rich composition appeared. These results may be ascribed to the coalescence of fine ZrO
2 crystals.
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Shigeo HAYASHI, Akira UENO, Kiyoshi OKADA, Nozomu OTSUKA
1991 Volume 99 Issue 1153 Pages
803-808
Published: September 01, 1991
Released on J-STAGE: August 06, 2010
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Powders of SrSiO
3 have been prepared by the sol-gel method using tetraethoxysilane and strontium hydroxide. Sinterability of the powder and microstructure and dielectric property of the sintered bodies have been examined. The powders densified without additives as sintering aid, however, sinterability and microstructure changed largely depending on the SrO/SiO
2 ratio and impurities. A small amount of ZrO
2 as impurity caused remarkable abnormal grain growth, and the formation of SrO-ZrO
2-SiO
2 glass was recognized at tripple point of grain boundaries. When the SrO/SiO
2 ratio exceeded unity, prismatic particles grew and impeded the densification. The starting batch composition containing 5mol% excess SrO gave the highest relative density of 98.2% throughout this study. On the other hand, liquid phase sintering by addition of BaO-Al
2O
3 components lowered the densification temperature. However, large closed pores remained in the microstructure and the range of sintering temperature became narrow. The dielectric constant of all the specimens was about 6.5 and dielectric loss was 1×10
-4-3×10
-4. The dielectric loss decreased with decreasing amount of grain boundary phase in the specimens.
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Toshiya KINOSHITA, Toru WAKABAYASHI, Hiroshi KUBO
1991 Volume 99 Issue 1153 Pages
809-812
Published: September 01, 1991
Released on J-STAGE: August 06, 2010
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The relation between grain morphology and mechanical properties has been extensively studied. Although mechanical properties are related to the real three-dimensional forms of grains, the real three-dimensional form can not be observed. Grains through a cross section can only be observed. The difference between the real three-dimensional and cross sectional form is large especially in rod-like grains. In this report, the aspect ratio of rod-like grains, which have a great influence on the mechanical properties, was studied. A relationship between the real three-dimensional aspect ratio (=
A) and the cross sectional aspect ratio (=
AR) was derived from model calculation;
AR=-ln{cos(tan
-1A)}+
A(π/2-tan
-1A). The model ueed assumed that the grains were rod-like, of uniform length and orientated randomly. The corresponding cross sectional aspect ratios were calculated to be 2.1, 2.6, 3.3, 4.0 for the real three-dimensional aspect ratios of 3, 5, 10 and 20. When the real aspect ratio is large, the difference between the real and cross sectional aspect ratios is also large. The calculated results were compared with the experimental data for a 20wt% SiC whisker-Si
3N
4 pressureless sintered body. Close agreement between calculated and experimental results was obtained.
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Katsunori YAMADA, Nobuo KAMIYA, Shigetaka WADA
1991 Volume 99 Issue 1153 Pages
813-816
Published: September 01, 1991
Released on J-STAGE: August 06, 2010
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Al
2O
3-SiC composites containing 0-40vol% SiC particles were prepared by hot-pressing. With an increase in SiC particle content, the hardness and fracture toughness of Al
2O
3-SiC composites increased from 17.1 to 24.4GPa and from 4.2 to 4.5MPa·m
1/2, respectively. Abrasive wear tests for SiC, Al
2O
3, Si
3N
4, TZP and α+β Sialon as well as Al
2O
3-SiC composites were carried out using SiC and Al
2O
3 abrasive papers. The volume wear rate was inversely proportional to the hardness and the fracture toughness of the materials. Al
2O
3-SiC composites containing more than 20vol% SiC particles showed better abrasion resistance than those of SiC, Al
2O
3, Si
3N
4 and TZP.
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Shigehisa ENDOH, Yoshikazu KUGA, Tomohiro ARAKIDA, Kazuo TAKEUCHI
1991 Volume 99 Issue 1153 Pages
817-818
Published: September 01, 1991
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This paper presents purification and crystallization of inorganic materials by laser zone refining (LZR), i.e., floating zone melting assisted by a high power infrared laser. The LZR heating system was composed of a Nd: YAG laser as a heat source, an optical fiber for laser beam transmission, and a focusing system. To determine LZR purification capabilities, 5mm zinc rods were melted and Pb impurity segregation was observed after refining the zinc rods. For the crystallization test, green bodies of 0.2μm α-Al
2O
3 fine powder were fused, and optically transparent single crystals were obtained. The LZR technique was found to be useful in the refining of inorganic materials.
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Norihiro MURAKAWA, Mutsuo NAKAJIMA
1991 Volume 99 Issue 1153 Pages
819-822
Published: September 01, 1991
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Fine SiC powders were obtained by heating SiO
2-C mixed powders synthesized by spraying a mixture of silicon tetrachloride and heavy oil into air-propane flame. By analyzing the properties of the SiC powders, it was found that agglomeration factor (Stokes diameter/BET diameter) can evaluate the degree of agglomeration, and SiC powders which had a low agglomeration factor exhibit a high green density and high sintered density.
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NOx Sensing
Yoshinobu NAKAMURA, Ryuji KOYAMA, Kunihito KOUMOTO, Hiroaki YANAGIDA
1991 Volume 99 Issue 1153 Pages
823-825
Published: September 01, 1991
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The oxidizing gas (NO
x or Cl
2) gas sensing characteristics of SiC/ZnO heterocontact were investigated. The current through the interface of SiC and ZnO under forward bias (SiC
+, ZnO
-) was decreased by the introduction of NO or NO
2 gas. For the generation of the NO
x gas sensing characteristics, the presence of water vapor is needed but too much water vapor spoiled the NO
x sensing characteristics. That is similar to the chlorine gas sensing characteristics of SiC/ZnO heterocontact reported previously. The present results suggest that the oxidizing power of the molecules is a key point for explaining the gas sensing mechanism of SiC/ZnO heterocontact at room temperature.
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Osamu OHTAKA, Takamitsu YAMANAKA, Shoichi KUME
1991 Volume 99 Issue 1153 Pages
826-827
Published: September 01, 1991
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Monoclinic hafnia (HfO
2) powders were treated from 400° to 1100°C and at a pressure from 3 to 6GPa. The products were identified by powder XRD. The results indicated that an orthorhombic phase was synthesized at pressures above 4GPa in the temperature range from 400° to 1000°C. Although the monoclinic-orthorhombic transition pressure is almost the same as that of ZrO
2, orthorhombic HfO
2 is more stable at high temperatures than ZrO
2. The Rietveld analysis showed that the orthorhombic HfO
2 is isostructural with one of the two orthorhombic ZrO
2 (ortho I).
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