Direct solid state NMR observation of titanium opens up new possibilities for characterization of many chemical problems. Here, solid state 47,49 Ti NMR spectra are reported for a large variety of crystalline ternary and quaternary titanates. A wide range of values for the NMR interaction parameters is observed, with chemical shifts covering ∼300 ppm and quadrupole interactions (C Q ) up to 24 MHz. The isotropic chemical shift (δ iso ) ranges for TiO 6 , TiO 5 , and TiO 4 deduced from these samples suggest that NMR can help to determine coordinations in materials where it is unknown, although the strong overlap of these ranges may not allow unequivocal identification in all cases. For TiO 6 units, there is a good correlation of the shear strain of the local TiO 6 unit to C Q . Similar correlations are found for the much rarer TiO 4 coordination. The correlation of C Q is generalized through the concept of a distortion index of the local structural unit, which applies to all TiO x units, including TiO 5 . Static NMR data from several samples (e.g., PbTiO 3 , Sr 2 TiO 4 ) show unequivocally that for some compounds titanium has a significant chemical shift anisotropy, which needs to be included for accurate simulations of static titanium NMR spectra. The electric field gradient determined by NMR does not agree with values previously obtained by perturbed angular correlation. Calculations of the quadrupole parameters using the WIEN97 code, based on the linearized augmented plane wave method, have been carried out for some perovskite-and ilmenite-structured titanates and agree well with the values determined from NMR (i.e., within a few percent), except for the ilmenite form of CdTiO 3 where the current structure appears unreliable. The 43 Ca NMR spectrum is reported for CaTiO 3 showing that C Q ) 2.15 ( 0.03 MHz, η ) 0.70 ( 0.07, and δ iso ) 17.2 ( 1.0 ppm.

No abstract

ECM Nancy s145 conference abstracts o.m1.o5 Computational simulations of novel a-site substituted perovskites. V.