To relate continuum theories of elastic phenomena to typical atomic or molecular theories, one needs some way of correlating changes in positions of the entities in the latter with descriptions of deformation used in the former. For crystals, the most commonly used bridge used for this is the Cauchy—Born rule. In recent years, there has been a flurry of activity aimed at better understanding it and in trying to generalize it. I will describe and comment on important ideas that have been generated, point out some successes and failures of the rule and indicate kinds of applications that have motivated such work.

On the Cauchy—Born Rule:

This article reviews at an introductory level the main concepts used in the description of ferroelasticity and other related properties of crystals, viz. ferrobielasticity, ferroelastoelectricity, ferromagnetoelasticity, ferrotrielasticity, and ferrogyrotropy. The symmetry and phase-transition aspects of these properties are emphasized; these aspects also form the basis for understanding the domain structure of these crystals. The relationship between ferroelastic transitions and martensitic transitions is explored. A brief discussion of the existing and potential applications of ferroelastic and related materials is also included.

Ferroelasticity and related properties of crystals

A method for the examination of crystal sections using penetrating characteristic X radiation

Band structure of transition metal oxides plays a critical role in many applications such as photo-catalysis, photovoltaics and electroluminescent devices. In this work we report findings that the band structure of MoO3 can be significantly altered by a distortion in the octahedral coordination structure. We discovered that, in addition to epitaxial type of structural strain, chemical force such as hydrogen inclusion can also cause extended lattice distortion. The lattice distortion in hydrogenated MoO3 led to a significant reduction of the energy gap, overshadowing the Moss-Burstein effect of band filling. Charge doping simulations revealed that filling of conduction band drives the lattice distortion. This suggests that any charge transfer or n-type electron doping could lead to lattice distortion and consequentially a reduction in energy gap.

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Impact of lattice distortion and electron doping on α-MoO3 electronic structure

Investigations under hydrothermal conditions

THE extensive use of quartz in piezoelectric oscillators has stimulated the production of synthetic quartz crystals Spezia1 in 1906 grew quartz at a temperature somewhat below 300° C from an aqueous solution containing sodium metasilicate and sodium chloride His method was to dissolve quartz in the hotter part of the container and deposit it in the cooler part We have repeated Spezia's experiments so far as to confirm his results, but the period of months which is required for appreciable growth to occur makes the method unsuitable for industrial production

Preparation of Synthetic Quartz

IN the Dauphine twins of quartz, the polarity of the electric axes is reversed on either side of a twin boundary. Structurally the change is slight. It has been known for some time that electrical twinning could be induced either by heating1 or by pressure2; but up to the present its elimination has not, so far as we are aware, been reported.

Control of Electrical Twinning in Quartz

DURING recent years there has been considerable interest both in Europe and the United States in the synthesis of quartz crystals large enough for use as piezo-electric oscillators in telecommunication equipment. An isothermal process for growing such crystals was described by Nora and W. A. Wooster1 in 1946 and a similar method was developed independently in Germany during the Second World War by Nacken2. The isothermal process depends on the high solubility of silica glass relative to that of α-quartz under hydrothermal conditions. In our most successful experiments we were able to deposit a total of nearly 1 mm. of good-quality quartz on to a seed crystal, cut parallel to a rhombohedral face, in an 18-hr, growth-cycle. However, difficulties were incurred in attempting to prolong the growth-cycle beyond a day, due to the devitrification of the silica glass3. We therefore re-examined alternative methods employing a temperature gradient, such as Spezia4 used in his pioneer experiments.

Growth of large quartz crystals.

CRYSTALS of molybdenum trioxide, prepared by subliming MoO3 powder, obtained from the pure ammonium compound, have been examined with X-rays. The crystals were small, thin, lustrous plates, parallel to b (010).

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Crystal Structure of Molybdenum Trioxide

WHERE a sizable crystal is to be used for investigations of structure-sensitive properties, for example, X-ray intensity measurements, photo-electric effect, etc., it is advisable to test its homogeneity. This may be simply done in the following way.

Nora Wooster

Papers

Preparation of Synthetic Quartz

Control of Electrical Twinning in Quartz

Growth of large quartz crystals.

Crystal Structure of Molybdenum Trioxide

X-Ray Topographs