摘要:

High‐purity single crystals of PbZrO3suitable for electrical measurements were grown from solutions in the PbO‐ZrO2‐PbF2‐B2O3system. Dielectric, hysteresis‐loop, and optical measurements confirmed the existence of an intermediate ferroelectric (FE) form, previously observed only in ceramics, just below the transition temperature (Tc#232°C). The temperature stability range of the FE phase, which cooling curve measurements show to vary from 12° to 26°C, appears to be related to crystal stoichiometry. The maximum value of spontaneous polarization isP8(max)#24 μC/cm2, assuming that the FE phase possesses rhombohe

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb11303.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

The abraded surface of polycrystalline BaTiO3was examined by X‐ray diffraction methods. The distorted layer produced by abrasion on 320‐grade SiC consists of (1) a region extending to the bottom of the deepest scratches in which the domains tend to be oriented with their c axes perpendicular to the surface and (2) a transition layer below this in which the orientation varies with depth. The orientation changes little on annealing until recrystallization begins at #900°C; however, annealing at 1100° to 1400°C produces an α‐domain reorientation. Possible explanations for these effects are discussed in terms of dislocations introduced by deformation during abrasion and grain size in the recrystallized surf

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb11304.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

A model is proposed to explain the phenomenon of electrode “polarization” in glasses containing alkali oxides. The application of a dc potential to Pt electrodes on an alkali‐containing glass causes a large electric field to develop in the immediate vicinity of the anode. This high‐field region is formed by local dissociation of the alkali oxides and displacement of the dissociated ions from the region. A major hypothesis of the model is that the nonbridging oxygen ions in this region can move and can determine the electrical characteristics of the sample. Large electric fields can also develop at a partially blocking cathode as a result of the pileup of alkali ions beneath the cathode surface. Permanent compositional changes occur near both electrodes under such conditions. The model was confirmed by dc electrical measurements, electron‐microprobe data, and oxygen‐evolution data. Important physical parameters of the model were calculated fr

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb11305.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

The high‐temperature thermal expansion of monoclinic Nb2O5was studied with X‐ray and dilatometric techniques. The X‐ray axial thermal expansion was anisotropic; the mean coefficients in thea, b, andcdirections, respectively, were 5.3, 0, and 5.9×10−6°C‐1from room temperature to 1000°C. It is proposed that this anisotropy causes microcrack formation in sintered polycrystalline samples. The bulk linear thermal expansion of both sintered and hot‐pressed samples was determined with a dilatometer from room temperature to 1200°C. A hysteresis effect between heating and cooling data observed for sintered samples was attributed to the occurrence and recombination of inter

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb11306.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Room‐temperature strengths are reported for titania and aluminum silicate in various biaxial stress states. Results are compared with failure criteria based on either energy or internal‐friction concepts. In general, more complete and reliable data for ceramic materials are needed before specific failure criteria can be designa

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb11307.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

High‐purity polycrystalline MgO and Al2O3were thermally grooved at 1500° and 1600°C. Accurate techniques were developed for following the growth of a single groove. For high‐purity samples growth kinetics were essentially similar to those reported in the literature but were determined to be controlled by volume diffusion. Specimens for thermal grooving were prepared from Al2O3to which transition metal oxides (Fe2O39, MnO, and TiO2), which are known to accelerate shrinkage and sintering of Al2O3powder compacts, had been added; the rate of groove growth was increased remarkably by minor amounts of these additives. Control of partial pressure indicated that Fe2+and Ti4+are the species active in promoting groove growth. Substantial evidence was found for volume diffusion as the mechanism controlling groove form

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb11308.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Morphological stages in the internal crystallization of a 3BaO‐ 5SiO2glass were investigated. Spherulitic crystallization occurred between 800° and 950°C. After long times at the crystallization temperatures, the spherulites changed, apparently by secondary crystallization. Above 950°C, lath‐like crystals are formed by recrystallization of the spherulites. The effects of nucleation‐and‐growth heat treatments on the rate and morphology of crystallization were studied. The peak nucleation temperature was between 700° and 725°C, and all the crystalline forms wer

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb11309.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Ultrasonic interferometry was used to measure elastic‐wave velocities and moduli in six Na2O‐TiO2‐SiO2glasses; three glasses contained 20 mol% TiO2and three 25 mol% TiO2. The elastic moduli and their pressure derivatives varied systematically with the SiO2/Na2O molar ratio of the glasses. In the group of glasses which contained 20 mol% TiO2,dK/dP(K=bulk modulus) decreased linearly from 4.85 to 2.59 as the SiO2/Na2O ratio increased; in the other group,dK/dPdecreased from 4.00 to 3.05. Similarly,dμ/dP(μ=shear modulus) decreased with the SiO2/Na2O ratio, but somewhat non‐linearly. The extrinsic and intrinsic contributions to the temperature dependencies of the elastic moduli are evaluated in light of the measured pressure dependencies of the

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb11310.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

The glass‐forming regions were investigated for pseudobinary systems of the compositionXMmSen‐(1–X)Ge1.5As0.5Se3(MmSen=PbSe, CdSe, BaSe, ZnSe, or La2Se3). Systems containing PbSe, CdSe, and BaSe contain substantial regions of glass formation, and differential scanning calorimetry, electron microscopy, and water corrosion tests were used to characterize these glasses. The glasses were generally phase‐separated, and the available data suggest that for PbSe melts the region of liquid‐liquid immiscibility spans almost the entire pseudobinary composition range. A few studies of glass formation were conducted for CdSe‐MmSen‐Ge1.5As0.5Se3pseudoternary and MmSen‐Ge

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb11311.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Proportionalities were developed which are felt to express melt oxygen activity and free‐oxygen‐ion activity in amber glass melts. These expressions indicate that increased modifier levels generally increase melt oxygen activity. The field strength of the modifier cations is also involved in determining the melt oxygen activity. Glasses with higher field strengths resulted in lower melt oxygen activities. Compositional changes also affected the level of dissolved water retained by the glasses. Direct and indirect polarization influences on bridging‐oxygen sites were felt to play a dominant role in determining water concentration. Alkalis with higher field strengths and high SiO2levels favored higher water‐retention

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1972.tb11312.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY