NMR studies of CuInS₂ and CuInSe₂ crystals grown by the Bridgman method

Bridgman-grown polycrystalline CuInS₂ and CuInSe₂ containing 2 at.% excess S and Se, respectively, were investigated by ⁶³Cu and ¹¹⁵In NMR. ⁶³Cu lineshapes were obtained at 79.83 MHz within the temperature range of 123<T<473 K. Line-shapes from both samples are similar and are typically broadened by first-order electric quadrupolar interactions with average coupling constant magnitudes of 0.54 MHz; whereas, the central transition reveals broadening due to chemical shift anisotropy. Temperature dependent motional narrowing of the copper line is observed with CuInSe₂; the associated diffusion coefficient is 3×10^-13 cm²/s at 473 K. The dependence of the paramagnetic shift with temperature suggests a complex form of magnetic ordering between unpaired spins.