Line shifts under pressure

The most common pressure sensor for optical studies is ruby (AI2O3 Cr3+, Piermarini et al. (1975)), whose strong Ri and R2 luminescence line shifts under pressure have been calibrated up to 180 GPa at room temperature (Mao et al., 1978 Mao, 1989). At low temperatures the line position has to be corrected by a known temperature-induced shift (Noack and Holzapfel, 1979). Besides ruby also other sensors utilizing rare-earth ions have been proposed and discussed in literature (Shen et al., 1991). In most of these cases the pressure induced shifts of luminescence lines are used to determine the pressure (see sect. 4.5). 

Figure 25 (a) Linear relation between (1/7 1)1/2 and the 13C-NMR frequency in K Qo under pressure leading to the determination of the chemical shift and (b) In Tc versus the reciprocal Knight shift under pressure. The continuous line is the BCS prediction. (After Ref. 94.)... 

Stress in crystalline solids produces small shifts, typically a few wavenumbers, in the Raman lines that sometimes are accompanied by a small amount of line broadening. Measurement of a series of Raman spectra in high-pressure equipment under static or uniaxial pressure allows the line shifts to be calibrated in terms of stress level. This information can be used to characterize built-in stress in thin films, along grain boundaries, and in thermally stressed materials. Microfocus spectra can be obtained from crack tips in ceramic material and by a careful spatial mapping along and across the crack estimates can be obtained of the stress fields around the crack. ... 

Fig. 3. Shift of the excitation line peaks of LaCl3 Pr3+ under pressure at 20 K. The assignment of the lines can be gathered from the level diagram on the right side. CG denotes the center of gravity of the D2 multiplet.

Selected average values for line shifts of different f elements under pressure. In all cases only the average Unear coefficient is given, slight deviations are neglected... 

A wide range of experimental techniques has thus been developed to meet the specific requirements of different isotopes, as illustrated in Fig. 3.44 for absorbers under pressure. The soft 7-rays (6.2 keV) of Ta can pass only through thin beryllium windows, however, due to the very narrow natural line width, changes in the isomer shift can be observed very accurately for this tantalum isotope—even in the 500 MPa region—with conventional hydraulic systems. 

The observed relaxation rate of 4 at 4.2 °K is small compared to that of a metallic system, but quite high for an insulating material at liquid helium temperatures (326). An investigation of spin-lattice relaxation time and nmr line shift of i sPt in K2Pt(CN)4Bro.3o(H20)3 under hydrostatic pressure has been reported in the temperature range between 78 °K and 300 °K and pressures up to 20 kbar (539). At temperatures above 120 °K an increase in pressure decreases the relaxation rate appreciably. In addition, the temperature interval in which the nmr shift changes continuously decreases under pressure. 

If the state point starts from point P, the shift along Rayleigh line has two directions up to point S with pressure increase, and down to point W (it corresponds with the under-pressure detonation) with pressure drop. Under suitable environmental conditions, under-pressure detonation is also possible when the pressure continuously decreases in the detonation wave range. 

Mossbauer measurements on Euo.25Lao.75Rh2 under pressure have been made by Wortmann et al. (1976). They found a strong pressure induced shift of the resonance lines which they explained by an increase in the energy separation between the Eu " and Eu " valence states. We note that Bauminger et al. (1976) have recently reported Mossbauer measurements on the Eu(A, 6)2 (A = Rh, Ir, B = Pt, Al) systems. 

The thermodynamic aspect of the metallization of substances under pressure is considered in [131,132], It is well-known (seeFig. 2.2 in Chap. 2), that the potential curve crosses the zero line of the dissociation energy (Eu) twice at thermal expansion when the induced heat = Eo (thermal dissociation) and at the compression when the repulsion energy of approaching atoms = Eo (pressure dissociation). From the quantum-chemical calculations of Slater [133] it follows that when atoms in a molecule are brought closer to one another, the valence electrons are shifted from the... 

Pressure Zero shift, air leaks in signal lines. Variable energy consumption under temperature control. Unpredictable transmitter output. Permanent zero shift. Excessive vibration from positive displacement equipment. Change in atmospheric pressure. Wet instrument air. Overpressure. Use independent transmitter mtg., flexible process connection lines. Use liquid filled gauge. Use absolute pressure transmitter. Mount local dryer. Use regulator with sump, slope air line away from transmitter. Install pressure snubber for spikes. 

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