NMR Studies of Mixed Y3?xYbxAl5O12 Crystals

Abstract

27Al NMR studies of the Y3—xYbxAl5O12 mixed garnets were performed. The magnetic moment of Yb3+ ions in the garnets was determined. The quadrupole coupling constants were calculated for Al in a‐ and d‐positions. It was shown that the mixed garnets with x = 0.75 and 1.00 should be treated as partially ordered solid solutions. A model of substitutional ordering for these mixed garnets was suggested.

Anomalous resonances in 29Si and 27Al NMR spectra of pyrope ([Mg,Fe]3Al2Si3O12) garnets: effects of paramagnetic cations

“…Only the mean magnetic moment of the paramagnetic Yb 3+ cations was considered in the analysis, but again useful information about cation distributions were obtained. 40 An early single-crystal 27 Al NMR study of a very iron-rich natural garnet reported a similar phenomenon. 39 In a high-resolution NMR study of powders of Tb 3+ -containing Y 3 Al 5 O 12 , additional 89 Y MAS NMR peaks appeared at higher dopant concentrations and were attributed to pseudo-contact interactions, while resonances for both this nuclide and 27 Al were severely broadened at high Tb contents.…”

“…For single crystals of mixed Y 3Àx Yb x Al 5 O 12 (''YAG'') garnet, large electron-nuclear dipolar shifts in 27 Al resonances were observed as a function of crystal orientation in the external field. 40 Most or all of such shifts would be averaged by MAS or by tumbling in a liquid, leaving only a residual contribution or pseudocontact effect if the magnetic susceptibility at the paramagnetic site is anisotropic. Only the mean magnetic moment of the paramagnetic Yb 3+ cations was considered in the analysis, but again useful information about cation distributions were obtained.…”

“…38 A number of single crystal (primarily 27 Al) NMR studied have been made on garnets, some of which have described large line splittings due to unpaired electron-nuclear dipolar interactions, which are strongly orientation-dependent, but which are expected to be averaged to zero by rapid magic-angle spinning. 39,40 Most silicate garnets have cubic symmetry and a simple structure that can make them especially interesting as case studies in spectroscopy. In this report, we describe an example that appears to be quite unusual among high-resolution, solid state NMR investigations of silicates: pyrope garnets ([Mg,Fe] 3 Al 2 Si 3 O 12 ), which contain up to 3.5 wt% FeO and yet retain well-enough resolved 29 Si and 27 Al spectra to show discrete, shifted resonances for sites that are probably within the second cation shell of the paramagnetic centers.…”

27Al nuclear magnetic resonance studies of the Y3-xLuxAl5O12mixed garnets

“…Since nuclear magnetic resonance (NMR) characteristics such as chemical shift, line shape, and relaxation times are very sensitive to the local structure in crystals, NMR investigation should be quite fruitful for revealing the substitutional order in mixed crystals, especially in the case of weak ordering. In fact, NMR has been used to study the partial substitutional order in the Y 3−x Yb x Al 5 O 12 mixed garnets [9], in mixed yttrium-erbium aluminates [10], and in binary and ternary semiconductor solid solutions (see [5,11,12] and references therein). In [9,10], the 27 Al absorption line shape was analysed; various numbers of paramagnetic Yb and Er ions in the Al surroundings were detected due to large shifts induced by interaction with electron moments.…”

Solid-state NMR and short-range order in crystalline oxides and silicates: a new tool in paramagnetic resonances

“…For static (nonspinning) single crystals (or powders), the effects of paramagnetic cations are most likely dominated by large through-space dipolar couplings, which have long been measured to provide information on site occupancies. For example, in the 1 H and 19 F spectra of micas, the intensities of small dipolar-shifted resonances provided unique constraints on nonrandom association of Fe 2+ with OH À versus F À anions (Sanz & Stone, 1979); numerous 27 Al NMR studies of single crystals of yttrium aluminum garnet (YAG) laser materials with various paramagnetic (and optically active) rare earth dopants have indicated that random dodecahedral site mixing prevails (Charnaya et al, 1999;Vorob'ev et al, 1998), following an early report on an FeO-rich natural silicate garnet (Ghose, 1964). More modern approaches to high-resolution paramagnetic NMR, particularly in biomolecular solids, have been recently reviewed (Pintacuda & Kervern, 2013).…”