The structure of aluminophosphate glasses revisited: Application of modern solid state NMR strategies to determine structural motifs on intermediate length scales

Structure and properties of high Li2O-containing aluminophosphate glasses

“…7), most of aluminium atoms appear in a sixfold coordination environment and the rest as four-and five-fold coordinated. Previous studies of 27 Al NMR in potassium aluminophosphate glasses by Wegner et al 16 have shown the same behaviour of aluminium polyhedra for low contents of Al 2 O 3 as in the lithium aluminophosphate glasses. The proportion of AlO 4 tetrahedra progressively increases with the alumina content in the glasses until being practically the major aluminium species present.…”

“…The two smaller ones are assigned to five and fourfold coordinated aluminium at 10 ppm and 37 ppm, respectively. 16 The relative proportions have been estimated by using dmfit 17 with an average error of ±5%, being around 12% for AlO 4 and AlO 5 and 76% for AlO 6 , remaining approximately constant within the error limits for all glass compositions. Fig.…”

“…Finally, the resonance band at −11 ppm is attributed to new structural units formed through P-O-Al linkages. 16 The spectra have been fitted to Gaussian functions with dmfit software 17 and the results of the proportions of phosphate groups and their chemical shifts are given in Table 3. The proportion of the Q 2 -type phosphate groups increases with the alumina content.…”

Structure of Ternary Aluminum Metaphosphate Glasses

“…A previous NMR study on KÀAl phosphates considered only the compositions 0.5K 2 O 3 xAl 2 O 3 3 (0.5 À x)P 2 O 5 with 0.025 e x e 0.2, starting with an O/P ratio above the metaphosphate line. 21 Previous NMR studies of the structure of NaÀAl and PbÀAl metaphosphates 17,19 are extended in this work with the use of double-resonance techniques and, in the case of the NaÀAl system, by analyzing samples with higher Al concentrations and using faster magic angle spinning (MAS) in Al nuclear spin species, such as rotational echo double resonance (REDOR) and rotational echo adiabatic passage double resonance (REAPDOR), has been quite fruitful in the study of local and medium-range order in aluminumÀphosphate glasses. 21À24 The analysis of the 31 PÀ 27 Al coupling in the ternary glasses is a helpful tool to identify the presence of Q 2 1 and Q 2 2 units and to determine the environment of P atoms around Al, in order to probe two fundamental properties: the existence of a corner-sharing regime between Al and P polyhedra and the presence of AlÀOÀAl bonds.…”

Caracterização estrutural de vidros fluorofosfatos utilizando metodologias de RMN

“…Al MQMAS spectrum of the sample with x = 30 and Table 5 summarizes the results obtained for all the samples. 24,26,74 In Figure 18 the results for a fluoride free glass and a glass having the maximum F content are compared. The dipolar second moments (M 2 ) were obtained from the parabolic fitting in Equation 47 and the results are summarized in Table 6.…”