Softening of the Rotary Lattice Mode inK2PtBr6as Detected by Nuclear Quadrupole Resonance

1972 ◽  
Vol 6 (4) ◽  
pp. 1596-1604 ◽  
Author(s):  
Henry M. Van Driel ◽  
Maria Wiszniewska ◽  
B. Michael Moores ◽  
Robin L. Armstrong
Keyword(s):  
Nuclear Quadrupole Resonance ◽  
Lattice Mode ◽  
Quadrupole Resonance ◽  
Nuclear Quadrupole

Temperature and pressure variation of the 35Cl nuclear quadrupole resonance frequency in K2OsCl6

1970 ◽  
Vol 48 (20) ◽  
pp. 2411-2419 ◽  
Author(s):  
Robin L. Armstrong ◽  
Gregory L. Baker
Keyword(s):  
Resonance Frequency ◽  
Nuclear Quadrupole Resonance ◽  
Coefficient Of Thermal Expansion ◽  
Pressure Variation ◽  
Temperature Phase ◽  
Thermodynamic Relation ◽  
Lattice Mode ◽  
Quadrupole Resonance ◽  
Temperature And Pressure ◽  
Nuclear Quadrupole

Measurements of the temperature and pressure dependence of the 35Cl nuclear quadrupole resonance (NQR) frequency in K2OsCl6 are reported. The resonance frequency is measured at atmospheric pressure for temperatures from 4.2 to 430 °K and for five temperatures between 284 and 410 °K for pressures to 5000 kg cm−2. A second-order phase transition occurs at about 45 °K. In the high temperature phase all of the chlorine atoms are crystallographically equivalent. The analysis carried out deals exclusively with the data obtained in this phase. A thermodynamic relation is used to relate the experimental quantities (∂v/∂T)P and (∂v/∂P)T to the theoretical quantity (∂v/∂T)V. The latter quantity is calculated for a particular model to describe the motional averaging of the electric field gradient at the chlorine sites. The model adopted includes two distinct mechanisms—the usual Bayer–Kushida averaging mechanism and a mechanism resulting from the partial destruction of π bonding by the lattice vibrations. The thermodynamic relation is used in conjunction with the combined data for K2PtCl6, K2IrCl6, and K2OsCl6 to evaluate the validity of the model proposed. It is concluded that the model provides a consistent explanation of both the temperature and pressure variation of the NQR data. In addition, the analysis provides information on the nature of the molecular orbitals of the [MCl6]2− complex ion, gives a rough estimate of the ratio of the coefficient of thermal expansion to the isothermal compressibility, and lastly, yields a value for the average frequency of the rotary lattice mode in the three substances.

Investigation of the Rotary Lattice Mode in R2PtCl6 Compounds. I. From Measurements of the 35Cl Nuclear Quadrupole Resonance Frequency

1971 ◽  
Vol 49 (19) ◽  
pp. 2381-2388 ◽  
Author(s):  
Douglas F. Cooke ◽  
Robin L. Armstrong
Keyword(s):  
Resonance Frequency ◽  
Nuclear Quadrupole Resonance ◽  
Atmospheric Pressure ◽  
Nuclear Quadrupole Resonance Frequency ◽  
Published Data ◽  
Lattice Mode ◽  
Quadrupole Resonance ◽  
Temperature And Pressure ◽  
Nuclear Quadrupole ◽  
Static Lattice

Measurements of the temperature and pressure variation of the 35Cl nuclear quadrupole resonance (NQR) frequency in Rb2PtCl6 and Cs2PtCl6 are reported. The resonance frequency is measured at atmospheric pressure for temperatures from 4 to 500 K and at four temperatures between 290 and 380 K for pressures to 5000 kg cm−2. Previously published data for K2PtCl6 are also included in the analysis. Static lattice NQR frequencies are deduced. The differences between the static lattice frequencies are compared with the calculations of Smith and Stoessiger. Thermal averaging of the electric field gradient at a chlorine site is assumed to be dominated by the Q3, Q4, Q5, and Q6 internal modes of the PtCl6 octahedra and by the rotary lattice mode. The rotary mode frequencies are deduced; they are of similar magnitude and increase in the same sequence as the frequencies deduced from infrared and Raman data. An analysis of the pressure dependence of the NQR frequencies leads to pressure coefficients for the rotary mode frequencies. The influence of the cage of R atoms surrounding a PtCl6 octahedron is shown to increase through the series K2PtCl6, Rb2PtCl6, Cs2PtCl6. Finally, a thermodynamic analysis of the NQR data is presented which shows the importance of taking specific volume effects into account.

Potassium hexachloropalladate and potassium hexachloroplatinate: a comparative study using nuclear quadrupole resonance

1969 ◽  
Vol 47 (20) ◽  
pp. 2165-2169 ◽  
Author(s):  
Robin L. Armstrong ◽  
Douglas F. Cooke
Keyword(s):  
Temperature Dependence ◽  
Nuclear Quadrupole Resonance ◽  
Lattice Relaxation ◽  
Nuclear Quadrupole Resonance Frequency ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Lattice Mode ◽  
Quadrupole Resonance ◽  
Nuclear Quadrupole

Measurements of the temperature dependence of the nuclear quadrupole resonance frequency νQ and spin–lattice relaxation time T1 of the 35Cl nuclei in powdered samples of K2PdCl6 are reported. The data are qualitatively similar to earlier results for K2PtCl6 and are analyzed in the same manner. The temperature dependence of both νQ and T1 are dominated by the F1g rotary lattice mode of frequency ~ 41 cm−1. The data for K2PdCl6 and K2PtCl6 are compared and the parameters characterizing the NQR behavior tabulated. It is suggested that the quantitative explanation of the rather small differences observed might provide a challenging problem for a molecular orbital theorist.

Temperature and pressure variation of the 35Cl nuclear quadrupole resonance frequency in K2IrCl6

1970 ◽  
Vol 48 (14) ◽  
pp. 1649-1656 ◽  
Author(s):  
Gregory L. Baker ◽  
Robin L. Armstrong
Keyword(s):  
Resonance Frequency ◽  
Temperature Dependence ◽  
Nuclear Quadrupole Resonance ◽  
Oscillation Frequency ◽  
Torsional Oscillation ◽  
Nuclear Quadrupole Resonance Frequency ◽  
Lattice Mode ◽  
Quadrupole Resonance ◽  
Temperature And Pressure ◽  
Nuclear Quadrupole

Experiments to study the temperature and pressure variations of the 35Cl nuclear quadrupole resonance (NQR) frequency in K2IrCl6 are described. The resonance frequency at atmospheric pressure is measured from 3.08 °K (the antiferromagnetic transition temperature) to 470 °K. Measurements of the pressure dependence of the resonance frequency for pressures to 5000 kg cm−2 have been carried out at five temperatures between 281 and 393 °K. A multiple-mode method is adapted to include the effect of the destruction of π bonding by the lattice vibrations and is then applied to the analysis of the temperature variation of the resonance frequency. The temperature dependence of the oscillation frequency of the rotary lattice mode is deduced. The behavior of the torsional oscillation frequency is nearly identical with that observed in K2PtCl6. An analysis of the combined results of the temperature and pressure studies in K2IrCl6 and similar results in K2PtCl6 suggest that volume effects as well as the destruction of π bonding may be important for the explanation of the experimental temperature dependence of the NQR frequency.

Remote nuclear quadrupole resonance in solids

1993 ◽  
Vol 163 (10) ◽  
pp. 95 ◽  
Author(s):  
Vadim S. Grechishkin ◽  
Nikolai Ya. Sinyavskii
Keyword(s):  
Nuclear Quadrupole Resonance ◽  
Quadrupole Resonance ◽  
Nuclear Quadrupole
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