ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb15924.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Extensive solid solution was observed in the system Pb(Sc1/2/,Nb1/2,)1‐x,Tix,O3. In the range 0 ≤ x ≤ 0.425 a rhombohedral ferroelectric phase was stable at 25° C. In the range 0.45 ≤ x ≤ 1.00 a tetragonal ferroelectric phase was stable at this temperature. The phase diagram of the system below 500° C strongly resembles that of PbZrO3−PbTiO3. The compound Pb(Sc1/2Nb1/2)O3exhibited rhombohedral perovskite cell symmetry below the ferroelectric ↔ paraelectric transition temperature, and the angle a was acute. The radial coupling coefficient was 0.46 for the composition Sc1/2Nb1/2)0.575Ti0.4250O3. At 25°C this composition consisted primarily of the rhombohedral phase with a small amount of the tetragonal phase present. The ferroelectric ↔ paraelectric transition occurred over a temperature range in the rhombohedral phase field. The spontaneous polarization was finite at temperatures considerably above the temperature of the permittivity maximum for a given rhombohed

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb15925.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The only intermediate phase stable in air in the system ZrO2−TeO2is ZrTe3O8with a cubic, distorted, fluorite‐type structure. The compound melts congruently at 1014°± 5°C to an unstable liquid. Vaporization occurs, with loss of TeO2, at high temperatures with an activation energy of 64 kcal per mole of ZrTe3O8. No glass formation was observed in the

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb15926.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Thermally crystallized glasses of compositions (Li2,O2, MgO).Al2O3.nSiO2were studied by X‐ray powder diffraction methods. High‐quartz solid solution phases developed at relatively low temperatures and, forn3.5, transformed at higher temperatures to keatite solid solution phases. Associated phases, if present, were Mg spinel and/or cordierite, or a few other trace phases. Theacrystallographic axis (a0) of high‐quartz solid solutions decreased with increase of MgO and/or SiO2. Theccrystallographic axis (c0) decreased with increasing MgO; it also decreased with increasing SiO2, but only when MgO content was low. X‐ray diffraction photographs of single crystals of high‐quartz solid solutions of compositions LiaO.Al2O3.nSiO3demonstrated that the maintenance of a basic high‐quartz structure is the basis of the solid solution relation. Three modifications of the high‐quartz structure were recognized in the Li2O‐Al2O3−SiO3system. These modifications were based on the occurrence and positions of superlattice reflections. The high‐quartz solid solution from Li2O Al2O3−2SiO2, showing streaky reflections in its precession photographs, suggested a defective structure. The term “high‐quartz solid solution,” with or without additional prefixes specifying the compositional series and modification, was considered the preferred nomenclature for

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb15927.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The high‐field losses of adulterated lead zirconate‐titanate ceramics were compared on the basis of rates of temperature rise of standard‐size samples in the same transducer configuration. Systematic chemical modification in light of the ionic model of the perovskite structure was used to produce ceramics with widely varying high‐field behavior. High‐field losses could be greatly reduced by adulteration of either cation site with ions of lower than normal valency. At 1 at.% concentration, lowest losses were found with adulterants whose valence was one unit less than normal. The results are explained as stoichiometric effects. Normal air‐fired lead zirconate‐titanate ceramics are considered to be deficient in metal tons. Adulteration with subvalent cations reduces the iotal oxygen content of the ceramic and brings it toward true ABO3stoichiometry. Lowest losses are postulated for truly stoichio

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb15928.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The relative grain boundary energy and surface diffusion coefficient of aluminum oxide were determined by observing the thermal grooving behavior of a series of bi‐crystals containing symmetric tilt boundaries. The relative energy for high tilt angles (30° to 150°) was roughly constant and equal to 0.54. The variation of relative energy with tilt angle was consistent with a dislocation core model for grain boundaries. The surface diffusion coefficient was:The agreement of this value for a vacuum etch with previous data for etches in air ruled out the oxygen ion as a possible rate‐controlling diffusion sp

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb15929.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Phase equilibria were determined for the systems NiO‐Cr2O3−O2, MgO‐Cr2O3,‐O2, and CdO‐Cr2O3−O2from 450° to above 850° C and at oxygen pressures of from 2 to 3500 atm. Only two intermediate phases were found in the nickel system: NiCrO., (CrVO4structure) and the spinel NiCr2O4. The magnesium and cadmium systems are similar in that they have three analogous phases: the low‐temperature α‐MgCrO4and α‐CdCrO4(both with the CrVO4structure), the high‐temperature β‐MgCrO4and β‐CdCrO4(both with the α‐MnMoO4structure), and the spinels MgCr2O4and CdCr2O4. The cadmium system contains an additional phase, Cd2CrO

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb15930.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Previous data by other writers who infer the existence of aluminum suboxides in the solid state are critically discussed and alternatively interpreted. High‐temperature X‐ray diffraction patterns previously attributed to crystalline Al2O and AlO are identified as those of Al4C3and AlTaO2, respectively. The melting curve observed by Baur and Brunner, suggesting the existence of a compound of the approximate composition Al2O9, corresponds to the pseudobinary system Al2O3−Al4C3. TheT‐xmelting curve of the system Al2O3−Al was determined. There is no indication of the existence of crystalline aluminum suboxide, the only condensed phases being α‐Al2O3and Al. The liquidus indicates demixing of liquid Al and molten Al2O3. There is very limited intersolubility, and the addition of Al does not lower the melting point of Al2O3measurably. With these facts and some additional information from the literature about the gaseous species, theP‐T‐xdiagram of the system Al

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb15931.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Values given in the literature for the heat of formation of plutonium mononitride range from — 70 to — 76 kcal/mole. This paper shows that if estimated entropy and high‐temperature heat capacity data are used to derive a reasonable set of high‐temperature thermal functions for the mononitride, ΔH0f,298(PuN) values obtained by both second‐and third‐law methods from equilibrium data agree. The equilibrium data are from measurements reported in the literature and cover a range from 700° to about 3040°K. A calorimetric value of —70.2 kcal/mole reported for the PuN heat of formation appears to be in disagreement with the derived equilibrium value of — 76.0 kcal/mole, but this difference can be explained by a compo

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb15932.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Total vapor pressures of PuO2‐x, compositions were measured gravimetrically with tungsten Knudsen cells from 2070° to 2380°K. The vapor pressure equation for the composition approximating the congruent one, PuO1.82, iswhere Pc, is the pressure if the vapor is assumed to be entirely PuO2(g). The evaporation of PuO1.562was univari‐ant, indicating the presence of two condensed phases, and that of PuO1.62was bivariant from 2240° to 2380°K; this result confirms that the phase boundary of the PuO2‐x, phase remains at Pu1.61at temperatures close to the

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb15933.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY