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Journal ArticleDOI

ESR study of Ag2+ ions in KNO3

02 Mar 1995-Physica B-condensed Matter (North-Holland)-Vol. 205, pp 349-352
TL;DR: In this article, the presence of Ag 2+ centres was detected in γ-irradiated silver-doped potassium nitrate at LNT and principal values of g - and A -tensors were obtained.
Abstract: ESR studies on γ-irradiated silver-doped potassium nitrate at LNT indicated the presence of Ag 2+ centres. Principal values of g - and A -tensors are obtained. Admixture coefficients of d-orbitals have been calculated. On warming the sample the signals due to Ag 2+ centres disappeared at 140 K.
Citations
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Journal ArticleDOI
TL;DR: The crystal structures and magnetic properties of the roughly one hundred binary, ternary, and quaternary AgII and AgIII fluorides in the solid state are examined to suggest that properly hole- or electron-doped AgII fluorides might be good BCS-type superconductors.
Abstract: With the aim of gauging their potential as conducting or superconducting materials, we examine the crystal structures and magnetic properties of the roughly one hundred binary, ternary, and quaternary Ag(II) and Ag(III) fluorides in the solid state reported up to date. The Ag(II) cation appears in these species usually in a distorted octahedral environment, either in an [AgF](+) infinite chain or as [AgF(2)] sheets. Sometimes one finds discrete square-planar [AgF(4)](2-) ions. The Ag(III) cation occurs usually in the form of isolated square-planar [AgF(4)](-) ions. Systems containing Ag(III) (d(8)) centers are typically diamagnetic. On the other hand, the rich spectrum of Ag(II) (d(9)) environments in binary and ternary fluorides leads to most diverse magnetic properties, ranging from paramagnetism, through temperature-independent paramagnetism (characteristic for half-filled band and metallic behavior) and antiferromagnetism, to weak ferromagnetism. Ag(II) and Ag(III) have the same d-electron count as Cu(II) (d(9)) and Cu(III) (d(8)), respectively. F(-) and O(2-) ions are isoelectronic, closed-shell (s(2)p(6)) species; both are weak-field ligands. Led by these similarities, and by some experimental evidence, we examine analogies between the superconducting cuprates (Cu(II)/Cu(III)-O(2-) and Cu(II)/Cu(I)-O(2-) systems) and the formally mixed-valence Ag(II)/Ag(III)-F(-) and Ag(II)/Ag(I)-F(-) phases. For this purpose we perform electronic-structure computations for a number of structurally characterized binary and ternary Ag(I), Ag(II), and Ag(III) fluorides and compare the results with similar calculations for oxocuprate superconductors. Electronic levels in the vicinity of the Fermi level (x(2)-y(2) or z(2)) have usually strongly mixed Ag(d)/F(p) character and are Ag-F antibonding, thus providing the potential of efficient vibronic coupling (typical for d(9) systems with substantially covalent bonds). According to our computations this is the result not only of a coincidence in orbital energies; surprisingly the Ag-F bonding is substantially covalent in Ag(II) and Ag(III) fluorides. The electron density of state at the Fermi level (DOS(F)) for silver fluoride materials and frequencies of the metal-ligand stretching modes have values close to those for copper oxides. The above features suggest that properly hole- or electron-doped Ag(II) fluorides might be good BCS-type superconductors. We analyze a comproportionation/disproportionation equilibrium in the hole-doped Ag(II) fluorides, and the possible appearance of holes in the F(p) band. It seems that there is a chance of generating an Ag(III)-F(-)/Ag(II)-F(0) "ionic/covalent" curve crossing in the hole-doped Ag(II)-F(-) fluorides, significantly increasing vibronic coupling.

133 citations

Journal ArticleDOI
TL;DR: In this article, two silver-cerium oxide samples (Ag 10 ¼wt.%) were prepared by two different methods: impregnation and deposition-precipitation.

64 citations

Journal ArticleDOI
TL;DR: In this paper, electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR), and thermoluminescence (TL) were used to characterize the primary electron and hole trapping centers in a lithium tetraborate (Li2B4O7) crystal doped with Ag.
Abstract: Electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR), and thermoluminescence (TL) are used to characterize the primary electron and hole trapping centers in a lithium tetraborate (Li2B4O7) crystal doped with Ag. Three defects, two holelike and one electronlike, are observed after exposure at room temperature to 60 kV x-rays. The as-grown crystal contains both interstitial Ag+ ions and Ag+ ions substituting for Li+ ions. During the irradiation, substitutional Ag+ ions (4d10) trap holes and two distinct Ag2+ centers (4d9) are formed. These Ag2+ EPR spectra consist of doublets (i.e., the individual 107Ag and 109Ag hyperfine lines are not resolved). One of these hole centers is an isolated unperturbed Ag2+ ion and the other is a Ag2+ ion with a nearby perturbing defect. EPR and ENDOR angular-dependence data provide the g matrix and the 107Ag and 109Ag hyperfine matrices for the more intense isolated hole center. In contrast, the electronlike EPR spectrum produced during the irradia...

39 citations

Journal ArticleDOI
TL;DR: In this article, the effects of ionizing radiation on Ag-doped lithium tetraborate (Li2B4O7) crystals were investigated using EPR angular dependences.

11 citations

References
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Journal ArticleDOI
TL;DR: In this article, the EPR spectrum of copper doped in zinc fluoride has been analyzed and the observed g values led by a new method to a determination of the coefficients of the Kramer's doublet.
Abstract: With the aid of computer techniques, including a laboratory automation system, accurate computer simulation, and an accurate calculation method, the EPR spectrum of copper doped in zinc fluoride has been analyzed. The observed g values led by a new method to a determination of the coefficients of the Kramer's doublet. Copper hyperfine structure verified these values and fluorine transferred hyperfine structure gave a measure of covalency. The fractional orbital occupation showed predominantly σ bonding which is similar to other reported transition metal ions in ionic insulating crystals. Orbital reduction, though no doubt present, makes only an insignificant and undetectable contribution.

65 citations

Journal ArticleDOI
TL;DR: In this article, a paramagnetic resonance was studied for Ag in the 4d 9 configuration substituting for alkali ions in alkali chlorides, and two spectra were observed corresponding to the low and high temperature modifications of the same spectrum under a "dynamical" Jahn-Teller distortion.

57 citations

Journal ArticleDOI
TL;DR: In this paper, four paramagnetic species have been detected by ESR in single crystals of AgNO3 x irradiated at 77°K and the principal values and corresponding principal axes of the g tensors and hyperfine tensors have been determined.
Abstract: Four paramagnetic species have been detected by ESR in single crystals of AgNO3 x irradiated at 77°K The principal values and corresponding principal axes of the g tensors and hyperfine tensors have been determined An eight‐line spectrum, four doublets, is due to Ag++ A 24‐line spectrum, four sextets, has been assigned to a species believed to be AgNO3− A spectrum of four triplets characteristic of stationary NO2 molecules was observed in previously irradiated crystals and crystals doped with AgNO2 A spectrum consisting of two weak singlets is due to an unidentified species This is the only species stable at room temperature Discussions of the orientations, configurations, mechanisms for production, and annealing characteristics of the several species are given

30 citations