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.

81Br Nuclear Quadrupole Resonance of Cs2ZnBr4 and Crystal Stability of Compounds of A2MX4 Type

Abstract: The temperature dependences of 81Br nuclear quadrupole resonance frequencies and quadrupolar relaxation times of Cs2ZnBr4 were measured. The librational motion of [ZnBr4]2− about the Zn–Br axis parallel to the a axis in the crystal is more active than those about the other axes. The reason why this compound shows no phase transition can be accounted for by the molecular packing, especially the packing of [ZnBr4]2− along the a axis. General examination of the relative size of cation/anion in the class of compounds of A2MX4 type led to a criterion which may be used to rationalize existence and absence of a phase transition.

Valence Crossover of Ce Ions in CeCu2Si2 under High Pressure - Pressure Dependence of the Unit Cell Volume and the NQR Frequency

Abstract: The pressure dependence of the valence of Ce ions in CeCu2Si2 has been investigated by means of X-ray powder diffraction (XRPD) and nuclear quadrupole resonance (NQR) measurements. The high-pressure XRPD measurements were carried out at 12 K for CeCu2Si2 and CeCu2Ge2. Precise measurements under smoothly-applied pressure were achieved through the selection of the gasket material of a diamond anvil cell. The jump of the unit cell volume, which was reported previously in CeCu2Ge2, was not observed within the experimental accuracy, indicating the absence of a first-order valance transition. The pressure dependence of 63Cu-NQR frequency νQ measured in CeCu2Si2 was compared with that calculated from the measured lattice parameters. The νQ's were calculated for the two cases of LaCu2Si2 and CeCu2Si2, corresponding to localized and itinerant cases for \(4f\) electrons, respectively. The measured and calculated slopes dνQ/dP show good agreement. A small but significant deviation from the pressure-linear dependence...

Phase transition and anionic motion in solid [(CH3)2NH2]2SnCl6 as studied by the temperature dependence of 35Cl NQR frequencies and chlorine nuclear relaxation times determined with a pulsed NQR spectrometer

Abstract: The temperature dependence of 35Cl NQR frequencies of [(CH3)2NH2]2SnCl6 was precisely determined between 78 and ca. 250 K. by means of an FT NQR spectrometer. The high-frequency line of the two 35Cl NQR signals having the intensity ratio of 2:1 already reported was observed to be split below 102 K. into sharp and broad lines with approximately equal integrated intensify. This clearly indicates the occurrence of a structural phase transition of a second-order nature at this temperature. The presence of phase transition around this temperature has been anticipated from the IR and NQR studies previously done. The temperature dependence of chlorine nuclear spin-lattice relaxation time, T1Q shows a dip with a clear depression at 102 K. The mechanism of the phase transition is discussed from the T1Q results and the fact that the frequency separation of the doublet increases with decreasing temperature. Above 180 K, T1Q of both lines decreased rapidly and the log T1Q vs. T−1 curves were almost linear. This decrease of T1Q was explained through the onset of the C4 reorientation of the anions with the activation energy of ca. 35 kJ mol−1. The fade-out phenomenon of the two NQR lines occurring far below room temperature can be well explained by the onset of the above motion with the very low activation energy.

Superconductivity and magnetism of Bi2Sr2CaCu2Ox : effect of quenching and pulverization

Abstract: The effect of quenching on Bi 2 Sr 2 CaCu 2 O x (BSCCO) has been investigated. Quenching enhances the critical temperature T c . The hole concentration n h (∼ 5 × 10 21 cm −3 ) decreases as the quenching temperature T q increases. The normal-state static susceptibility χ DC (∼ 5 × 10 −7 emu/g) of the BSCCO pellet is almost independent of temperature but its magnitude decreases with the increase of T q . Thermogravimetry (TG) analysis shows that the change in the oxygen content is very small when the sample is heated. The Cu nuclear quadrupole resonance (NQR) spectra are very broad. In addition, we have observed a large Curie-Weiss term in χ DC and χ ESR of powdered samples. From the Curie constant, the number of localized Cu 2+ spins is estimated to reach 30% of total Cu atoms. This component almost disappears by re-annealing. In all cases, χ ESR has almost the same magnitude as χ DC , in marked contrast with YBa 2 Cu 3 O 7−δ . The origin of the normal-state susceptibility is discussed.