Structural characterization of noncrystalline solids and glasses using solid state NMR

Correlation between the real part of the dielectric constant and the structure of glasses in the system AsxSe1−x and GexSe1−x is reported. The mole polarization is calculated using the Sellmeyer approximation neglecting the Lorentz field. The vibrationally caused part of the permittivity which is obtained by subtraction of the mole refraction reflects ordered states in the investigated series. Besides the known crystalline compounds As2Se3 and As4Se4 the formation of the vitreous AsSe3 and As3Se2 from the liquid state has to be supposed. In the system GexSe1−x the formation of the compounds GeSe2 and Ge2Se3 is completed by GeSe4 which as Ge2Se3 obviously only exists in the non-crystalline state. GeTe4 has been reported as a metastable crystalline phase. The temperature dependence of ϵr of vitreous As2Se3 is tentatively interpreted in terms of the dipole orientation caused by conversion of the charge in valence alternation pairs.

Glass formation and properties of chalcogenide systems XXVI: Permittivity and the structure of glasses AsxSe1−x and GexSe1−x

The structures of phosphorus-selenium glasses PxPe1−x with x=0 (pure selenium), 0.05, 0.15, 0.25, 0.40 and 0.50 have been investigated with neutron diffraction, extented, X-ray absorption fine structure measurements, and Raman and infrared spectroscopy. The behavior of the near-neighbor coordination at r∼2.3 A as a function of x suggests a picture in which P4Sen molecular units are linked together by Se atoms or chains. The diffraction patterns exhibit anomalous peaks at Q ∼ 1.2A which rise dramatically as P is added to the Se glass; these peaks can also be understood on a molecular picture. The Raman spectra at the larger P concentrations are characterized by series of relatively sharp peaks which also suggest molecular units and for x = 0.5 bear a close correspondence to the spectrum of crystalline P4Se3.

The structure of phosphorus-selenium glasses I. Concentration dependence of the short- and intermediate-range order☆

Studies on the structure of the bulk glasses GeS2 with the aid of X-ray diffraction measurements and RDF calculations are reported which are supported by pair function calculations based on a wire model constructed by hand which has been approximated in three steps in order to guarantee the isotropy criteria and the experimental density preferentially taking into consideration the bond parameters of the high temperature modification of crystalline GeS2. Because of the comparatively sufficient accordance between the model RDF and the experimental RDF up to the third peak and with respect to the peak positions even up to the fifth maximum the glass structure can be approached by a three-dimensional connected network of GeS 4 2 units, about one fourth of which are edge shared with a GeSGe angle distribution of 85–145° and a maximum at about 115°. The RDF of vitreous GeSe2 is discussed in comparison with GeS2.

Glass formation and properties of chalcogenide systems XXXII. RDF studies on the structure of vitreous Ge2S3 and Ge2Se3

The detailed quantitative speciation of phosphorus and selenium microstructures in phosphorus-selenium glasses is derived from combined $^{31}\mathrm{P}$ spin-echo and magic-angle-spinning NMR experiments. The results illustrate that the structure of these glasses differs from the chemically ordered or clustered structures previously proposed, but are also at variance with a completely random distribution. There is a distinct preference for the formation of P-Se versus P-P and Se-Se bonds, which can be quantified from the present experiments. The site speciation shows no dramatic changes near the composition (40 at.% P) corresponding to the rigidity percolation threshold.

Quantitative determination of the structural units in phosphorus-selenium glasses by 31P dipolar and magic-angle-spinning NMR spectroscopy.

The properties of chalcogenide glasses that are most important for applications as infrared transmitting materials are reported and their mutual relationships are given. The requirements for the intrinsic transmission of the materials and the reasons for their limitation are discussed. Based on structural interpretations of the optical parameters, combinations of glasses for the apochromatic correction of objectives are proposed. The relations between thermal properties, mechanical strength and stress-induced birefringence are shown and suitable compromises for proper applications are deduced.

Optical glasses for ir transmittance

Zur Glasbildung in den Systemen Phosphor‐Selen und Phosphor‐Schwefel

Chalkogenidgläser als infrarotdurchlässige optische Medien

Zur glasbildung in den systemen phosphor-selen und phosphor-schwefel

Review: Ubersicht uber glasbildende Chalkogenidsysteme, ihre Struktur und Stabilitat, die Darstellung optischer Chalkogenidglaser, die Transparenz der Glaser, Brechzahl und Dispersion sowie Spannungsdoppelbrechung.

Dietmar Linke

Papers

Optical glasses for ir transmittance

Zur Glasbildung in den Systemen Phosphor‐Selen und Phosphor‐Schwefel

Chalkogenidgläser als infrarotdurchlässige optische Medien

Zur glasbildung in den systemen phosphor-selen und phosphor-schwefel

Chalcogenide glasses as infrared‐transparent optical media