The electric field gradient in noncubic metals

The first application of the projector augmented wave method to calculate electric-field gradients is presented. The projector augmented wave method is an all-electron electronic structure method that provides an accurate description of the wave function near the nucleus, and thus is well suited to the prediction of hyperfine parameters. Electric-field gradients have been evaluated for a variety of molecules and crystals containing main-group and transition-metal elements. Our results compare well with experiment and previous calculations based on the linear augmented plane-wave method.

Electric-field-gradient calculations using the projector augmented wave method

The recoilless emission and resonant absorption of low energy γ-rays by solids (Mossbauer effect) are reviewed, with particular reference to the present and future applications to solid state and nuclear physics.

http://iopscience.iop.org/article/10.1088/0034-4885/25/1/311/pdf

The mössbauer effect

The quadrupole hyperfine interaction of111Cd in Cd, In, Sn, and of67Zn,69Ge in Zn was measured with high accuracy using TDPAC and TDPAD methods; in addition the systems117In in Cd and In, and113Sn in Cd were investigated. The temperature dependence of the electric field gradienteq(T) can be reproduced by the simple relationeq(T)/eq(0)=1—B⋅T
3/2 over a range of temperatures from a few K up to the melting point. A comparison with other experiments was carried out to test the universality of this empirical relation. In particular, high precision NQR experiments on Ga, In and Sb strongly support this relation. It is discussed whether lattice vibrations can explain the observed temperature variation or whether the experimental data indicate the need for a new description. Some new ideas suggesting a basically different model are given.

Temperature dependence of the electric field gradient in noncubic metals

The Cu63 and Cl35 pure quadrupole relaxation times have been measured by rf pulse techniques in cuprous oxide, paradichlorobenzene, 2,2‐dichloropropane, t‐butyl chloride, and methylene chloride at temperatures from 77°K to room temperature. The Cu63 T1 data agree with the ionic lattice model. The Cl35 T1 data for paradichlorobenzene agree with a torsional molecular‐oscillator model. For 2,2‐dichloropropane the Cl35 T1 values agree with a model based on field‐gradient fluctuations produced by reorienting CH3 groups. The more complicated T1 temperature dependences observed in t‐butyl chloride and methylene chloride appear to be the result of multiple thermal motions. The same can be said of our limited data on the Cl35 relaxation in 1,2‐dichloroethane. No discernible difference was found for the relaxation times of the two Cl35 resonance lines in methyl chloroform at 77°K.In general, the available proton T1 and linewidth data correlate well with our chlorine results; this agreement is discussed. The chlorine spin phase memory times are governed by the local magnetic fields except when decreased by spin—lattice lifetime broadening. The inverse linewidth parameters exhibit broadening by a distribution of field gradients. The fadeout of the Cl35 quadrupole resonance with increasing temperature in 2,2‐dichloropropane is the result of T1 broadening, while in t‐butyl chloride and methylene chloride it is produced by phase transitions.The Bayer model for spin—lattice relaxation by molecular torsional oscillations is treated in some detail, including a new approach which dispenses with some of his simplifying assumptions. A brief analysis is given of T1 for the case in which field‐gradient fluctuations are produced by random, large‐angle reorientations of groups near to the relaxed nucleus. The theory is presented for a null method of measuring the pure quadrupole T1. The method, which was used in most of our measurements, is similar to the Carr—Purcell 180°—90° pulse method for measuring nuclear magnetic T1's.The Cu63 and Cl35 pure quadrupole relaxation times have been measured by rf pulse techniques in cuprous oxide, paradichlorobenzene, 2,2‐dichloropropane, t‐butyl chloride, and methylene chloride at temperatures from 77°K to room temperature. The Cu63 T1 data agree with the ionic lattice model. The Cl35 T1 data for paradichlorobenzene agree with a torsional molecular‐oscillator model. For 2,2‐dichloropropane the Cl35 T1 values agree with a model based on field‐gradient fluctuations produced by reorienting CH3 groups. The more complicated T1 temperature dependences observed in t‐butyl chloride and methylene chloride appear to be the result of multiple thermal motions. The same can be said of our limited data on the Cl35 relaxation in 1,2‐dichloroethane. No discernible difference was found for the relaxation times of the two Cl35 resonance lines in methyl chloroform at 77°K.In general, the available proton T1 and linewidth data correlate well with our chlorine results; this agreement is discussed. The chlorin...

Nuclear Pure Quadrupole Relaxation and Its Temperature Dependence in Solids

Dependence of the Pure Quadrupole Resonance Frequency on Pressure and Temperature

The pressure dependence of the knight shift in the alkali metals and copper

The properties of a thermometer based upon the temperature variation of the pure quadrupole resonance frequency (ν0) of the Cl35 nucleus in granular KClO3 have been investigated. In the range ∼10°K<T <300°K, the thermometer has a very high sensitivity, being better than ±0.002° at 273°K and ±0.004° at 77°K. The accuracy at 20°K is estimated as at least ±0.02°. The thermometer is exactly reproducible if care is taken that the KClO3 is of high chemical purity. No hysteresis effects were observed. Establishment of the thermometer requires a single precise determination of the ν0 versus temperature curve using the fundamental temperature standards to measure the temperature.

T. Kushida

Papers

Dependence of the Pure Quadrupole Resonance Frequency on Pressure and Temperature

The pressure dependence of the knight shift in the alkali metals and copper

Precise nuclear resonance thermometer

Nuclear magnetic resonance in antiferromagnetic mnf2 under hydrostatic pressure