Thermal Properties Of Crystals Research Articles

On the Self‐Consistent Statistical Theory of Anharmonic Effects in Imperfect Crystals

AbstractThe improved unsymmetrized self‐consistent field method developed in preceding papers is used to study anharmonic effects in imperfect crystals. Various one‐dimensional models of anharmonic crystals with defects are considered: vacancy, free surface, adsorption with taking into account the influence of adatoms on the adsorbent, and substitutional impurities. The formulae for the lattice relaxation near defects, for the effective amplitudes of the anharmonic vibrations of atoms, and for the Helmholtz free energy are obtained. They are expressed in terms of the nearest‐neighbour interaction potentials and their derivatives of several orders at the equilibrium points. A comparison with known results for some harmonic models is made. The decisive role of the anharmonicity in such effects as the temperature dependence of the lattice relaxation and the influence of the imperfections on thermal properties of crystals is emphasized. The possibility of application of the method to three‐dimensional imperfect crystals, as well as of taking into consideration the interactions with next neighbours is noted.

Application of the thermodynamic theory of perturbations to the calculation of the thermal properties of crystals

Expressions are obtained in the quasiharmonic approximation with the help of the thermodynamic theory of perturbations for the derivatives of the free energy of a lattice with respect to the components of the strain tensor in terms of the Green temperature functions and the corresponding derivatives of the potential energy and the second-order coupling parameters. A modified version of the quasiharmonic approximation is proposed for the calculation of the temperature dependence of the thermal properties of crystals.

Magnetoelastic interaction in rare-earth systems. II. Specific heat, thermal expansion and elastic constants

For pt.I see ibid., vol.14, p.4311 (1981). The authors compute the corrections to the thermal properties of crystals which contain rare-earth ions. These corrections arise fom magnetoelastic interaction. It is shown that different thermal properties contain the same free parameters and hence fitting must be done simultaneously.

Influence of Lattice Constant Fluctuations on the Thermal Properties of Crystals

physica status solidi (b)Volume 93, Issue 1 p. K5-K8 Short Note Influence of Lattice Constant Fluctuations on the Thermal Properties of Crystals C. Malinowska-Adamska, C. Malinowska-Adamska Institute of Physics, Technical University of ŁódźSearch for more papers by this authorL. Wojtczak, L. Wojtczak Institute of Physics, University of ŁódźSearch for more papers by this author C. Malinowska-Adamska, C. Malinowska-Adamska Institute of Physics, Technical University of ŁódźSearch for more papers by this authorL. Wojtczak, L. Wojtczak Institute of Physics, University of ŁódźSearch for more papers by this author First published: 1 May 1979 https://doi.org/10.1002/pssb.2220930154AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Volume93, Issue11 May 1979Pages K5-K8 RelatedInformation

X-ray camera for study of crystals at low temperatures

The design of a compact constant temperature chamber which can be used for X-ray studies of thermal properties of crystals at any steady temperature between — 185°C. and +200°C. is described. The adaptation of this thermostat for taking Laue, oscillation and back reflection photographs is also described. The advantages and disadvantages of the present design are discussed in detail.

Structure and thermal properties of crystals, VI. The role of hydrogen bonds in Rochelle salt

X-ray measurements have been made of changes in the lattice spacings of Rochelle salt between —90 and +40° C. Rough visual estimates have also been made of changes in the intensities of X-ray reflexions with temperature. The thermal properties of Rochelle salt have been correlated with its crystal structure. As with other crystals containing hydrogen bonds, thermal expansion is largest in the direction of these bonds, but above the upper Curie point this predominance largely disappears. Between the two Curie points the thermal expansion shows anomalies and is subject to hysteresis. Two main theoretical problems are discussed in the light of the observations. In the first place, the thermodynamic changes at the lower and upper Curie points have hitherto appeared to be transitions ‘of the second kind’, occurring within single crystals without change of phase. Fresh X-ray evidence shows that over the transition range of temperatures measurable differences can be detected between subcrystalline domains within a ‘single’ crystal. These differences reach a maximum value in certain directions in the crystal, but appear to be insufficient to cause it to break up into powder, with change of phase, at the two Curie points, so that most of the properties of a single crystal are retained over the whole range of temperatures. The experimental conclusions throw light on the general theory of phase transitions of the second kind. Secondly, the onset of anomalous dielectric properties at the lower Curie point is ascribed to the stretching of short hydrogen bonds owing to the thermal expansion of the crystal. This changes the bonds from a non-polar to a polar character and is correlated with thermal effects in other crystals containing hydrogen bonds. In extension of apparatus previously described a new controlled temperature chamber has been devised, which has been used with various X-ray cameras for single crystal work at temperatures down to — 90° C.

Structure and thermal properties of crystals. V. Thermal expansion of phthalocyanines and porphins

Measurements have been made on the changes in lattice spacing of various phthalocyanines, over a range of temperatures from 90 to 600° K. Rough visual estimates have also been obtained of changes in the intensities of reflexions with rise in temperature. The molecular movements in the crystals have been calculated from the experimental data. Attention is drawn to the difference in behaviour of hydrogen and platinum phthalocyanines, which is probably due to the increased space required by the platinum atoms as the temperature rises, compared with the hydrogen in hydrogen phthalocyanine. Apparatus described includes a new design of furnace, suitable for use with various X-ray cameras for single crystal work, and a moving film oscillation camera, which uses the multiple exposure principle to determine small changes in lattice spacing with high relative accuracy.