We present a manometer designed to measure pressures of 1–20 kbar in temperatures between 4–300 K in cylinder‐piston type chambers, with an accuracy of ∼100 bar. The manometer is based on pressure‐dependent zero‐field 63Cu nuclear quadrupole resonance frequency corresponding to ‖±3/2〉↔‖±1/2〉 transition in Cu2O. The nuclear quadrupole resonance frequency νQ varies linearly with pressure and its temperature dependence is adequately explained by a model of lattice vibrational modes in O—Cu—O bonds. This manometer is particularly convenient for zero or high‐field magnetic resonance experiments.

Cuprous oxide manometer for high-pressure magnetic resonance experiments

We have developed a new type of opposed-anvil high pressure cell with substantially improved space efficiency. The clamp cell and the gasket are made of non-magnetic Ni–Cr–Al alloy. Non-magnetic tungsten carbide (NMWC) is used for the anvils. The assembled cell with the dimension φ29 mm ×41 mm is capable of generating pressure up to 9 GPa over a relatively large volume of 7 mm 3 . Our cell is particularly suitable for those experiments which require large sample space to achieve good signal-to-noise ratio, such as the nuclear magnetic resonance (NMR) experiment. Argon is used as the pressure transmitting medium to obtain good hydrostaticity. The pressure was calibrated in situ by measuring the fluorescence from ruby through a transparent moissanite (6H-SiC) window. We have measured the pressure and temperature dependences of the 63 Cu nuclear-quadrupole-resonance (NQR) frequency of Cu 2 O, the in-plane Knight shift of metallic tin, and the Knight shift of platinum. These quantities can be used as reliable...

Space Efficient Opposed-Anvil High-Pressure Cell and Its Application to Optical and NMR Measurements up to 9 GPa

We report C63u nuclear quadrupole resonance (NQR) measurement of Cu2O under pressure up to about 10 GPa at low temperatures. Because the lattice parameter of Cu2O changes with increasing pressure, the electric field gradient at the Cu site also changes correspondingly with pressure. This enables us to use the Cu2O as an in situ manometer for high pressure nuclear magnetic resonance/NQR up to about 9 GPa.

Manometer extension for high pressure measurement: nuclear quadrupole resonance study of Cu2O with a modified Bridgman anvil cell up to 10 GPa.

The electric field gradient (EFG) at the 63Cu nucleus of Cu2O and CuO has been measured as a function of pressure using the nuclear quadrupole resonance frequency (vQ). The value of ( delta ln vQ/ delta P)T was 1.40+or-0.02(1.33+or-0.05) Mbar-1 for Cu2O at 295 (77) K and 5.4+or-0.1 Mbar-1 for CuO at 295 K. The value of ( delta ln vQ/ delta ln V) for Cu2O is -1.5, showing that Cu2O is not a purely ionic compound, as is often assumed in the analysis of the EFG of high Tc superconductors. The magnitude of ( delta ln vQ/ delta P) tau for 63Cu in CuO suggests that meaningful measurements of the pressure dependence of vQ in the high Tc superconductors can be made at easily accessible pressures.

Pressure dependence of the electric field gradient at the 63Cu nucleus of Cu2O and CuO; implications for the analysis of NQR measurements on high Tc superconductors

High pressure technique up to about 3GPa is now widely used in studies of condensed matter physics. This is due to the development of hybrid cylinder clamp cells, especially CuBe/NiCrAl and CuBe/MP35N. Further high pressures can be achieved by Bridgman anvil cell (up to about 10GPa), cubic anvil cell (up to about 20GPa) and diamond anvil cell (up to about 400GPa), and so on. Optical measurements and electric resistivity measurement with the use of the diamond anvil cell are now conventional methods for high pressure measurements beyond about 100GPa. However, other major measurements such as neutron diffraction, nuclear magnetic resonance (NMR), nuclear quadrupole resonance (NQR), and muon spin relaxation ( SR) have technical difficulty since large sample space is essentially needed for these methods. Of these methods, NMR/NQR under high pressure is relatively accessible. We indeed reported Cu-NQR measurements of Cu2O up to about 10GPa by using a modified Bridgman anvil cell which is designed for general-purpose pressure cell. In our previous NQR measurements of Cu2O, the spectral broadening was observed and was nearly proportional to pressure P. This was ascribable to the existence of inhomogeneous pressure distribution inside the cell and/or local shear of the crystalline lattice, induced by the uniaxial stress of the inhomogeneous pressure. A reason of the pressure inhomogeneity except for the problem, originating from the Bridgman anvil cell itself, is that the pressure transmitting medium is already solid at high pressures. Generally, the solid pressure transmitting media make the pressure distribution inside the cell inhomogeneous. However, it is difficult to avoid solidification of the pressure media at high pressures. Hence, it is vital to choose the most appreciate medium for high pressure measurements. The NMR/NQR technique has an advantage to investigate the suitability of the pressure media because the pressure inhomogeneity inside pressure cell is strongly related to the broadening of NMR/NQR spectra. In this paper, we report Cu-NQR measurement of Cu2O with the currently representative liquid pressure-transmitting media. As the first step of the investigation, we demonstrated the NQR experiments under pressure up to about 3GPa at low temperature and room temperature. There are some reports on the liquid pressure-transmitting media, but few appeared in refereed journals. Moreover, to the best of our knowledge, there is no report of the evaluation and the comparison of the pressure media from the viewpoint of NMR/NQR technique. Therefore, we evaluated the pressure quality of the representative pressure-transmitting media by NQR. The Cu-NQR measurements of Cu2O were performed using a phase-coherent pulsed NQR spectrometer in the resonance frequency range 26–28MHz. We used commercial Cu2O powder (99.9%). We performed the NQR measurements at 4.2K and room temperature (about 300K). The obtained spin echo data were Fourier transformed to NQR spectra. In most cases, the line shape at a pressure was obtained at an excitation resonance frequency. We used conventional Cu-Be/NiCrAl hybrid piston cylinder cell. Single-layer coil wound about 20 turns was used in our measurements ( 1⁄4 3mm, l 1⁄4 5mm). The diameter of the initial sample space was 4.5mm and its length was 18mm. We used the following four representative liquid pressure-transmitting media: a 1 : 1 mixture of Fluorinert 70 and 77 (Fluorinert), Daphne 7373 oil (Daphne), a 1 : 1 mixture of n-pentane and isopentane (Pentane), and glycerin (Glycerin). We did not try a mixture of methanol and ethanol since this mixture sometimes dissolves the epoxy which is used for the pressure seal of the piston cylinder cell. Note that the configuration of the sample and the sample coil except for the pressure media was always the same inside the cell in order to compare the contribution of only the pressure media to the NQR spectra. The frequency f dependence of Cu-NQR resonance frequency of Cu2O up to about 9GPa can be used for a pressure manometer. In our previous NQR measurements of Cu2O, we revealed that the calibration formula reported by Reyes et al. is basically consistent with our extended calibration formula. Because our calibration formula was obtained only at low temperature, we used the calibration formula reported by Reyes et al. in this study, which covers the temperature range between 4.2 and 350K and the pressure range up to about 2GPa. We determined the pressure beyond 2GPa by the extrapolation of this formula. We clarified its appropriateness in our previous study. The calibration formulae are f ðP; 4:2KÞ 1⁄4 26:82þ 0:402P 1:496 10 P and f ðP; 300KÞ 1⁄4 25:99þ 0:355P 6:738 10 P. Here, f and P are in MHz and in GPa, respectively. With these formulae and the spectral center f of NQR of Cu2O, we derived pressure inside the cell. In Fig. 1, we show the P dependence of the full width at half maximum (FWHM) of Cu-NQR spectra of Cu2O with the various pressure transmitting media, Fluorinert, Daphne, Pentane, and Glycerin. The data are obtained at room temperature [about 300K, Fig. 1(a)] and 4.2K [Fig. 1(b)]. The accuracy of the data is within 5%. In the inset of Fig. 1(b), we show the Cu-NQR spectra of Cu2O obtained at room temperature under the pressures of 2.15GPa (Fluorinert) and 2.29GPa (Pentane). The most obvious feature of the results is the P dependence of the FWHM of the Fluorinert. The FWHM of the Fluorinert linearly increases with increasing P. This is clear in the inset of Fig. 1(b), which shows that the line shape of the Fluorinert is much broader than that of the E-mail: hideto@nmr.s.chiba-u.ac.jp Journal of the Physical Society of Japan Vol. 76, No. 12, December, 2007, 125001 #2007 The Physical Society of Japan

Evaluation of Pressure Transmitting Media by 63Cu-NQR of Cu2O

Temperature Dependence of Nuclear Quadrupole Resonance in Cuprous Oxide

A simple transistorized Zeeman modulator for nuclear quadrupole resonance spectroscopy is described. The instrument produces an antisymmetrical square-wave current into a Helmholtz coil. The maximum current is 1.3 A, sufficient to excite modulation fields of up to 100 G.

J. L. de Wildt

Papers

Temperature Dependence of Nuclear Quadrupole Resonance in Cuprous Oxide

Zeeman modulator for nuclear quadrupole resonance spectroscopy