ISSN:0232-1300    

DOI:10.1002/crat.2170250118

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractMicroscopic study of a number of commercial and laboratory quartz crystals grown from Na‐alkaline solutions at about 350 °C show that they always contain fluid and solid inclusions. More than 99% of the inclusions in normally grown crystals occur at the seed plate or very close to it, not further than 0.2–0.5 mm. The solid inclusions occur as single particles, in small groups or in clusters and aggregates containing hundreds of various inclusions. Dimensions of single particles vary from 1 ton· 10 μm but separate inclusions and especially aggregates can measuren· 100 μm. Normally, the number of solid inclusions is of the order ofn· 100 per cm2but in separate “patches” measuring up to several cm2the density reaches ton· 1000 per cm2. Regardless of the origin of the host crystal, the solid inclusions are always of three kinds: 1. Quartz microcrystals — husks, whiskers, needles, and elongated plates which comprise up to 30% of all inclusions; 2. Several still unidentified non‐quartz phases, tentatively designated as “silicates” — euhedral and anhedral crystals with its refractive index greater than the index of quartz, and fine or submicroscopic elongated crystals of low index, which amount to 70%; 3. Technogene impurities consisting of small irregular opaque particles of metal oxides and presumably graphite which occur only sporadically. The formation of solid inclusions depends probably much more on the surface tension th

ISSN:0232-1300    

DOI:10.1002/crat.2170250119

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe positions of 13 non‐hydrogen atoms in the structure of kaolinite from Keokuk, Iowa, were refined in the space group C1 using the constrained X‐ray Rietveld refinement. The precision and accuracy of the atomic positions are better than those previously reported. The most frequent e.s.d.'s of the positional parameters range from 0.003 to 0.005; the SiO bond distances are from the interval 1.56(4)–1.68(3) Å, and the AlO from 1.80 (5) to 2.07 (5) Å. The ditrigonalization angle α characteristic for tetrahedral sheet was found to be 9°, this value is in good agreement with the 11° reported from single crystal data. The correction for preferred orientation was in the form of exp (Gcos (2α)), the final factors of agreement wereRwp= 23.1%,RF=

ISSN:0232-1300    

DOI:10.1002/crat.2170250120

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractAn analytical theory for flexo‐electric domains in planar nematic films with positive dielectric anisotropy is proposed. It can be decided by a simple criterion, whether flexoelectric domains or the ordinary Fredericksz transition will occu

ISSN:0232-1300    

DOI:10.1002/crat.2170250121

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

ISSN:0232-1300    

DOI:10.1002/crat.2170250101

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY