125Te NMR for structural investigations in phase change materials: Optimization of experimental conditions coupled to NMR shift prediction

Effects of Ga Substitution on the Local Structure of Na2Zn2TeO6

In the work presented here, we prepared Ga-substituted NZTO (Na_2–xZn_2–xGa_xTeO₆, x = 0.00, 0.05, 0.10, 0.15, 0.20) layered materials with a soft chemical, citric acid-based synthesis method and characterized these by means of X-ray diffraction (XRD), ²³Na and ¹²⁵Te NMR, and by density functional theory (DFT) modeling. The influence of randomly distributed Ga cations on the ¹²⁵Te NMR spectra confirms the successful synthesis. With DFT-based linear response computations, we show that the local distribution of Na ions in the two neighboring interlayers influences the ¹²⁵Te chemical shift, consistent with observations. DFT modeling suggests that some of the Na sites are rarely occupied in pure NZTO but become favorable upon Ga substitution. There are clear indications that Ga substitution gives an uneven distribution of Na ions in neighboring interlayers and that the Na structure in one layer affects the adjacent layers.

The influence of randomly distributed Ga cations on the 125Te NMR spectra confirms the successful synthesis.