A first principles embedded cluster approach is used to calculate O chemical shielding tensors, σ, in prototypical transition metal oxide ABO3 perovskite crystals. Our principal findings are 1) a large anisotropy ofσ between deshielded σx ≃ σy and shielded σz components (z along the Ti-O bond); 2) a nearly linear variation, across all the systems studied, of the isotropic σiso and uniaxial σax components, as a function of the B-O-B bond asymmetry. We show that the anisotropy and linear variation arise from large paramagnetic contributions to σx and σy due to virtual transitions between O(2p) and unoccupied B(nd) states. The calculated isotropic δiso and uniaxial δax chemical shifts are in good agreement with recent BaTiO3 and SrTiO3 single crystal 17 O NMR measurements. In PbTiO3 and PbZrO3, calculated δiso are also in good agreement with NMR powder spectrum measurements. In PbZrO3, δiso calculations of the five chemically distinct sites indicate a correction of the experimental assignments. The strong dependence ofσ on covalent O(2p)-B(nd) interactions seen in our calculations indicates that 17 O NMR spectroscopy, coupled with first principles calculations, can be an especially useful tool to study the local structure in complex perovskite alloys.

First-principles density functional theory oxygen chemical shift tensors were calculated for A(B,B')O(3) perovskite alloys Pb(Zr(1/2)Ti(1/2))O(3) (PZT) and Pb(Mg(1/3)Nb(2/3))O(3) (PMN). Quantum chemistry methods for embedded clusters and the gauge including projector augmented waves (GIPAW) method [C. J. Pickard and F. Mauri, Phys. Rev. B 63, 245101 (2001)] for periodic boundary conditions were used. Results from both methods are in good agreement for PZT and prototypical perovskites. PMN results were obtained using only GIPAW. Both isotropic δ(iso) and axial δ(ax) chemical shifts were found to vary approximately linearly as a function of the nearest-distance transition-metal/oxygen bond length, r(s). Using these results, we argue against Ti clustering in PZT, as conjectured from recent (17)O NMR magic-angle-spinning measurements. Our findings indicate that (17)O NMR measurements, coupled with first-principles calculations, can be an important probe of local structure in complex perovskite solid solutions.

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