Temperature-dependent nuclear magnetic resonance inCuInX2 (X=S,Se,Te)chalcopyrite-structure compounds

Abstract

The NMR spectra of $^{63}\mathrm{Cu}$ and $^{115}\mathrm{In}$ in CuIn${\mathrm{S}}_{2}$, CuIn${\mathrm{Se}}_{2}$, and CuIn${\mathrm{Te}}_{2}$ have been measured between room temperature and 550\ifmmode^\circ\else\textdegree\fi{}C. The effects of motional narrowing and of phase transitions on the shape and width of the absorption spectra were evaluated. In all three compounds, the absorption signal of $^{63}\mathrm{Cu}$ shows motional narrowing. For ${\mathrm{Cu}}_{1.00}$${\mathrm{In}}_{1.00}$${\mathrm{S}}_{2.00}$ the mean jump frequency of the ${\mathrm{Cu}}^{+}$ ions, $\ensuremath{\nu}({\mathrm{Cu}}^{+})$, is $2\ifmmode\times\else\texttimes\fi{}{10}^{13}\mathrm{exp}[\ensuremath{-}\frac{(1.25\ifmmode\pm\else\textpm\fi{}0.10 \mathrm{eV})}{\mathrm{kT}}]$ ${\mathrm{s}}^{\ensuremath{-}1}$. For both CuIn${\mathrm{Se}}_{2}$ and CuIn${\mathrm{Te}}_{2}$, $\ensuremath{\nu}({\mathrm{Cu}}^{+})$ is about 3\ifmmode\times\else\texttimes\fi{}${10}^{3}$ ${\mathrm{s}}^{\ensuremath{-}1}$ at 350\ifmmode^\circ\else\textdegree\fi{}C. In copper-deficient ${\mathrm{Cu}}_{0.96}$${\mathrm{In}}_{1.02}$${\mathrm{S}}_{2.00}$ no motional narrowing of the $^{63}\mathrm{Cu}$ absorption was observed up to 550\ifmmode^\circ\else\textdegree\fi{}C. However, the $^{63}\mathrm{Cu}$ line shape in CuIn${\mathrm{S}}_{2}$ depends on the copper-to-indium ratio. A line-shape analysis as a function of composition shows that, at 450\ifmmode^\circ\else\textdegree\fi{}C, CuIn${\mathrm{S}}_{2}$ exists in the composition range between ${\mathrm{Cu}}_{1.00}$${\mathrm{In}}_{1.00}$${\mathrm{S}}_{2}$ and ${\mathrm{Cu}}_{0.85}$${\mathrm{In}}_{1.05}$${\mathrm{S}}_{2}$. For specimens with [Cu]/[In]>1, ${\mathrm{Cu}}_{2}$S contributes to the absorption signal. In a separate study of the $^{63}\mathrm{Cu}$ absorption in ${\mathrm{Cu}}_{2}$S, the hexagonal-to-cubic transformation was observed at 440\ifmmode^\circ\else\textdegree\fi{}C. The activation energy for $\ensuremath{\nu}({\mathrm{Cu}}^{+})$ in cubic ${\mathrm{Cu}}_{2}$S is 0.15 eV. The phase-transformation temperatures for the three $\mathrm{CuIn}{X}_{2}$ compounds (where $X$ is a group-VI element) were determined by differential thermal analysis. A previously unnoticed transformation was found in CuIn${\mathrm{Se}}_{2}$ at 665\ifmmode^\circ\else\textdegree\fi{}C. Finally, the quadrupole coupling constant ${\ensuremath{\chi}}_{q}$ ($^{63}\mathrm{Cu}$) of a number of $\mathrm{Cu}Z{X}_{2}$ compounds (where $Z$ is a group-III element) is shown to be a linear function of the tetragonal distortion parameter $\ensuremath{\delta}=2\ensuremath{-}\frac{c}{a}$ with $|{\ensuremath{\chi}}_{q}|=1.50+90\ensuremath{\delta}$ MHz. The value for $\ensuremath{\delta}=0$ is of the same order of magnitude as the result of a simple model of a point charge on a cubic lattice.