There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

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A comprehensive review of zno materials and devices

Recent developments of phosphate glasses for a variety of technological applications, from rare-earth ion hosts for solid state lasers to low temperature sealing glasses, have led to renewed interest in understanding the structures of these unusual materials. In this review, spectroscopic and diffraction studies of simple phosphate glasses, including v-P2O5 and binary phosphate compositions, are described. Special attention is given to the structures of anhydrous ultraphosphate glasses, which have received close attention from the glass community only in the past six years.

Review: the structure of simple phosphate glasses

Recent progress in processing and properties of ZnO

ZnO: growth, doping & processing

The present work illustrates the different contributions to the structure of phosphate glasses which are made by diffraction studies. The resolution in real space of the neutron diffraction experiments resolves two P–O distances. The lengths of the P–O bonds to the terminal and to the bridging oxygen atoms change as a function of the P2O5 content and of the species of the modifier cation. The model about the role of the properties of the modifier atoms, Me, in the structure of phosphate glasses predicts three different types of structural incorporation of these atoms. The experimental findings of a network change at ≈20 mol% modifier oxide content in range I are explained by a change of the interaction between the Me sites and the twofold-linked PO4 groups. For the intermediate cations a change of the Me–O coordination number, NMeO, is obtained which indicates a stabilization of Me–O–P bridges in range II. With increasing modifier content a situation commonly described as a modified random network ensues (range III) where clusters of MeOn polyhedra are formed. The corresponding consequences for the Me–Me distances from the relation between NMeO and the available number of terminal oxygen atoms per modifier cation are simulated by the reverse Monte Carlo method. This approach which makes use of the scattering information about the medium-range order is applied to the structures of binary metaphosphate glasses with Me=Zn, Ca, Sr, Ba, Na and K.

Structural specifics of phosphate glasses probed by diffraction methods: a review

A combination of results from x-ray and neutron diffraction is used to obtain structural information about the metal-oxygen coordination shell in oxide glasses. Two ways to extract structural parameters of the Me-O coordination are presented. The first variant is a direct combination of both distance correlation functions which are considered simultanously in a least-squares fit procedure. On the other hand a suitable difference of the two structure factors is introduced, which do not contain any O-O correlation. The corresponding distance correlation function directly shows the Me-O peak. The samples are metaphosphate glasses with Me = Al, Zn, Mg, Ca, Ba and Na and two sodium silicate glasses (76.5 and 67 mol% silicon dioxide). Four oxygens are found in contact to the Mg ion. But two additional, more distant positions are detected. Thus, the sum of all oxygen atoms in the coordination sphere is 6 rather than 4. The Zn cation is located in a real ZnO4-tetrahedron. The number of oxygens in the environment of the Na ion is of about five both in the metaphosphate glass and in the silicate glasses. But a surprising result is a splitting observed for the Na-O distance peak in case of silicate glasses.

https://iopscience.iop.org/article/10.1088/0031-8949/1995/T57/021/pdf

The oxygen coordination of metal ions in phosphate and silicate glasses studied by a combination of x-ray and neutron diffraction

31P NMR CW and FT MAS measurements have been used to investigate the structural composition of x(MeO)·(1−x)(P2O5) glasses (Me = Ca, Sr, Ba, x = 0.25−0.50). The influence of the structural composition on components of the chemical shift tensors is determined and discussed by means of a correlation between isotropic chemical shifts in crystalline phosphates and molecular structure published recently by Sternberg et al. [Z. Phys. Chem. Neue Folge 168 (1990) 115].

31P NMR investigations of binary alkaline earth phosphate glasses of ultra phosphate composition

X-ray diffraction measurements were performed on four (MeO)x(P2O5)(1 - x) glass series, with Me = Zn, Mg, Ca, Ba, and x ranging from about 0.05 to 0.6. The parameters for the MeO coordination sphere are determined. Abrupt changes in the ionic volume fraction are found for the glasses, with different Me ions, at certain compositions which correlate with the behaviour of the MeO coordination sphere. These phenomena can be explained in terms of a model based on the chemical characteristics of P2O5 and on the interplay between the number of non-bridging oxygen atoms per Me cation and changes in the type of the MeOm polyhedron.

The dependence of structural peculiarities in binary phosphate glasses on their network modifier content

Neutron diffraction has been used to determine the two P-O bond lengths which occur in the threefold-linked tetrahedral structural units of vitreous . The large maximum momentum transfer which is available on the LAD instrument at the ISIS spallation neutron source gives high real-space resolution which enables a clear separation to be made between P-O bond lengths involving terminal oxygens and those involving bridging oxygens . The two P-O distances in vitreous were found to have narrower distributions than have previously been observed, using the same experimental conditions, for any other modified phosphate glass.

https://iopscience.iop.org/article/10.1088/0953-8984/10/2/004/pdf

Dörte Stachel

Papers

Structural specifics of phosphate glasses probed by diffraction methods: a review

The oxygen coordination of metal ions in phosphate and silicate glasses studied by a combination of x-ray and neutron diffraction

31P NMR investigations of binary alkaline earth phosphate glasses of ultra phosphate composition

The dependence of structural peculiarities in binary phosphate glasses on their network modifier content

The P-O bond lengths in vitreous probed by neutron diffraction with high real-space resolution