Temperature dependence of nuclear quadrupole resonances in ²³⁵U-depleted Cs₂UO₂Cl₄

In this work, we report zero field ³⁵Cl nuclear quadrupole resonance (NQR) for ²³⁵U-depleted Cs₂UO₂Cl₄. A single peak indicates that all Cl ions are at an equivalent site. A good agreement between electric field gradients obtained from the spectrum and a DFT calculation confirms partial charge transfer between Cl and U. The resonance frequency decreases linearly with temperature at high temperatures and with decreased slope at lower temperatures. The temperature dependence of the spin-lattice relaxation time shows a quadratic decrease at high temperature and accelerated change at low temperature. Calculations using phonon induced charge fluctuation in covalent hybridization show good agreement with experimental observations. By comparing experimental data and theory, we obtained a Debye’s temperature, T_D=100 K. An estimate of the contribution of Cl ions to the U NQR frequency shifts and spin-lattice relaxation can be obtained from this analysis.