Nuclear quadrupole resonance

About: Nuclear quadrupole resonance is a research topic. Over the lifetime, 3531 publications have been published within this topic receiving 38801 citations. The topic is also known as: Nuclear quadrupole resonance spectroscopy & NQR.

Nuclear quadrupole spin–lattice relaxation due to molecular reorientations in crystals with orientational disorder

Abstract: p-chloronitrobenzene (PCNB) and p-chlorobromobenzene (PCBB) crystallize in the centrosymmetric space group P21/c with two molecules per unit cell. The space lattice will have an equal number of points with molecules facing in opposite directions. As a consequence, these compounds exhibit an orientational rigid disorder. In this work, we have measured the temperature dependence of the chlorine nuclear quadrupole spin–lattice relaxation time (T1), linewidth, and resonance frequency for both compounds for temperatures higher than 80 K. Both compounds exhibit an inhomogeneously broadened line shape and a “normal” Bayer-type temperature dependence of the resonance frequency. The analysis focuses on the identification of the dominant relaxation process at high temperatures (T>240 K in PCNB and T>260 K in PCBB). It is shown that T1(T) reflects the existence of 180° molecular reorientations through a modulation of the crystalline contribution to the electric field gradient.

Cu NQR Study of Impurity and Host Spin Dynamics in YBa2(Cu1-xNix)4O8

Abstract: We report nuclear quadrupole resonance (NQR) measurements of the 63 Cu nuclear spin-lattice relaxation times in YBa 2 (Cu 1- x Ni x ) 4 O 8 ( x =0, 0.005, 0.010 and 0.020) using a spin-echo techniq...

Electric-field-gradient analysis of high-tc superconductors

Abstract: The qualitative and quantitative features of the electronic charge distribution in cuprate superconductors are reexamined on the basis of a comprehensive set of nuclear quadrupole resonance and NMR measurements. A systematic analysis of measured electric-field gradients is performed within the tight-binding approach, commonly used for electronic models in cuprates. Both in-plane and out-of-plane sites and orbitals are considered. Special attention is given to the generic pd model involving only the σ orbitals in the CuO2 planes. This model is checked against the experimental data. The physical origin of several material-dependent features is clarified. It is shown that in La2-xSrxCuO4 the 3d3z2-r2 orbital of the in-plane copper and the 2pz apex oxygen orbital are occupied by a substantially smaller fraction of holes than the in-plane σ orbitals, at variance with proposals lending importance to copper-apex oxygen hybridization. At the in-plane oxygen site a sizable 2pz admixture is found at the Fermi level of YBa2Cu3O7. The in-plane charge distribution of Tl2Ba2CuO4 is found to be qualitatively similar to that of the high-temperature tetragonal phase of La2-xSrxCuO4. It appears that the additional holes are shared among copper and oxygen sites in similar proportions. This is shown to be compatible with the large Ud Emery model provided that the difference between the p and d atomic energies is comparable to the first neighbor overlap energy.

Nuclear Quadrupole Coupling Constants in Niobium Pentachloride and Related Compounds (I) Halogen Nuclei

Abstract: 35 Cl NQR spectrum in NbCl 5 has been investigated from 42 K to 480 K The lines of about 7 MHz have larger multiplicity and show positive temperature dependence incontrast to the usual negative one for the line of about 13 MHz The former lines are further separated into two groups having different temperature dependences The expressions for the chlorine coupling constant are derived according to Townes-Dailey's method on the basis of the p π -d π bond The NQR data are analysed and the lines are assigned to the axial, equatorial and bridging chlorine atoms in the Nb 2 Cl 10 dimer The theory is applied to other related compounds