An experimental technique using powders is described which permits the rapid classification of materials according to(a) magnitude of nonlinear optical coefficients relative to a crystalline quartz standard and(b) existence or absence of phase matching direction(s) for second‐harmonic generation.Results are presented for a large number of inorganic and organic substances including single‐crystal data on phase‐matched second‐harmonic generation in HIO3, KNbO3, PbTiO3, LiClO4·3H2O, and CO(NH2)2. Iodic acid (HIO3) has a nonlinear coefficient d14∼1.5×d31 LiNbO3. Since it is readily grown from water solution and does not exhibit optical damage effects, this material should be useful for nonlinear device applications.

A Powder Technique for the Evaluation of Nonlinear Optical Materials

Relationships between the carbon-oxygen stretching frequencies of carboxylato complexes and the type of carboxylate coordination

This review summarizes recent developments in the theory of spin glasses, as well as pertinent experimental data. The most characteristic properties of spin glass systems are described, and related phenomena in other glassy systems (dielectric and orientational glasses) are mentioned. The Edwards-Anderson model of spin glasses and its treatment within the replica method and mean-field theory are outlined, and concepts such as "frustration," "broken replica symmetry," "broken ergodicity," etc., are discussed. The dynamic approach to describing the spin glass transition is emphasized. Monte Carlo simulations of spin glasses and the insight gained by them are described. Other topics discussed include site-disorder models, phenomenological theories for the frozen phase and its excitations, phase diagrams in which spin glass order and ferromagnetism or antiferromagnetism compete, the Ne\'el model of superparamagnetism and related approaches, and possible connections between spin glasses and other topics in the theory of disordered condensed-matter systems.

Spin glasses: Experimental facts, theoretical concepts, and open questions

Phase-change materials are some of the most promising materials for data-storage applications. They are already used in rewriteable optical data storage and offer great potential as an emerging non-volatile electronic memory. This review looks at the unique property combination that characterizes phase-change materials. The crystalline state often shows an octahedral-like atomic arrangement, frequently accompanied by pronounced lattice distortions and huge vacancy concentrations. This can be attributed to the chemical bonding in phase-change alloys, which is promoted by p-orbitals. From this insight, phase-change alloys with desired properties can be designed. This is demonstrated for the optical properties of phase-change alloys, in particular the contrast between the amorphous and crystalline states. The origin of the fast crystallization kinetics is also discussed.

Phase-change materials for rewriteable data storage

A new set of covalent atomic radii has been deduced from crystallographic data for most of the elements with atomic numbers up to 96. The proposed radii show a well behaved periodic dependence that allows us to interpolate a few radii for elements for which structural data is lacking, notably the noble gases. The proposed set of radii therefore fills most of the gaps and solves some inconsistencies in currently used covalent radii. The transition metal and lanthanide contractions as well as the differences in covalent atomic radii between low spin and high spin configurations in transition metals are illustrated by the proposed radii set.

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Covalent radii revisited

The atomic arrangement in glass

A classie work, so thoroughly revised as to be essentially a new book. The changes include: a new mineral classification; a new elastic series of classification numbers for species; new data derived from x-ray crystallography, and a new form of presentation of crystallographic data; revision of specific gravities, based on new observations; introduction of the optical characters of the opaque minerals; a new chemical treatment of species; a new method of treating a series of minerals as if it were a single-species description; expansion of the annotation and reference section. Ready in June. Seventh Edition, Volume I: Approx. 803 pages; 6 by 9; Probable price, $8.50

Theory of X-Ray Diffraction in Crystals

(1) To point out what I believe to be an error in his paper concerning the physics of diffraction in perfect crystals, and (2) to call to the attention of X-ray crystallographers certain aspects of two papers (Werner & Arrott, 1965; Werner, Arrott, King & Kendrick, 1966) a thesis (Werner, 1965) and a laboratory report (Werner & Arrott, 1964) on neutron diffraction which have a direct bearing on the extinction problem.

A general theory of X‐ray diffraction in crystals

The paper gives brief descriptions of new structure types observed for simple compounds of the 5f-series of elements and of related elements.

Crystal chemical studies of the 5f-series of elements. I. New structure types

It is shown that Darwin's formula for the secondary extinction correction, which has been universally accepted and extensively used, contains an appreciable error in the x-ray diffraction case. The correct formula is derived. As a first order correction for secondary extinction, Darwin showed that one should use an effective absorption coefficient mu + gQ where an unpolarized incident beam is presumed. The new derivation shows that the effective absorption coefficient is mu + 2gQ(1 + cos/sup 4/2 theta )/(1 plus or minus cos/sup 2/2 theta )/s up 2/, which gives mu + gQ at theta =0 deg and theta = 90 deg , but mu + 2gQ at theta = 45 deg . Darwin's theory remains valid when applied to neutron diffraction. (auth)

W. H. Zachariasen

Papers

The atomic arrangement in glass

Theory of X-Ray Diffraction in Crystals

A general theory of X‐ray diffraction in crystals

Crystal chemical studies of the 5f-series of elements. I. New structure types

The secondary extinction correction