Uniaxial pressure

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. ... 

Hot pressing requires a refractory die, pressure and heat sources and temperature- and pressure-indicating devices. For many applications the die containing the sample to be hot pressed is heated either by a separate furnace (for < 1000°C) or by inductive or resistance heating of the die body itself. Uniaxial pressure is applied through the ram of a hydraulic or pneumatic press. 

Yano, T, Inouye, Y. and Kawata, S. (2006) Nanoscale uniaxial pressure effect of a carbon nanotube bundle on tip-enhanced near-field Raman spectra. Nano Lett., 6, 1269-1273. 

An initial attempt was made to correlate the structural properties of the kl-(BEDT-TTF)2M(CF3)4(TCE) salts with their superconducting transition temperature [31]. The relationship between Tc and any single unit cell parameter failed to show any discemable trend. The best correlation was obtained by plotting Tc as a function of the b/c ratio, where b is the interlayer and c is an intralayer direction. A similar conclusion was reached through the determination of uniaxial pressure coefficients of p -(BEDT-TTF)2SF5CH2CF2S03 and k-(BEDT-TTF)2Cu(NCS)2 through the measurement of thermal expansion [32]. These results also indicated that expansion of the interlayer direction and compression of an intralayer direction... 

Fig. 19. Shift and splitting of the hydrogen vibrational energy in passivated Si caused by uniaxial pressure along [100] and [112] lattice directions. [Reprinted with permission from the American Physical Society, Herrero, C.P., and Stutzmann, M. (1988). Phys. Rev. B 38, 12668.]...

Fig. 20 Diagram of the possible motions of the B—H complex in Si. Possible displacements of the H atoms with (a) increasing temperature and (b) under strong uniaxial pressure are shown. [From Stutzmann and Herrero (1988).]...

Fig. 3 Variation of Tc with the average mass of oxygen for STO18-100x closed circles) and -containing samples open circles). The broken line shows fitted results. Comparisons with the results of Ca substitution (a) and uniaxial pressure experiment (b) are shown...

One of the consequences of the suppression of the phase transition is the presence of a special critical point, Tc = 0 K. This point, called the quantum displacive limit, is characterized by special critical exponents. Its presence gives rise to classical quantum crossover phenomena. Quantum suppression and the response at and near this limit, Tc = 0 K, have been extensively studied on the basis of lattice dynamic models solved within the framework of both classical and quantum statistical mechanics. Figure 8 is a log-log plot of the 6 T) results for ST018 [15]. The expectation from theory is that in the quantum regime, y = 2 at 0.7 kbar, after which y should decrease. The results in Fig. 8 quantitatively show the expected behavior however, y is < 2 at 0.70 kbar. Despite the difference in the methods to suppress Tc in ST018, the results in Fig. 4a and Fig. 8 are quite similar. As shown in the results in Fig. 3b, uniaxial pressure also can be a critical parameter S for the evolution of ferroelectricity in STO. 

Haefner, K., and H. Dachs Domain rearrangement in NiF with magnetic fields and uniaxial pressure. J. Chem. Phys. 43, 2910 (1965). 

Fig. 18 Temperature-uniaxial pressure phase diagram in the low temperature region of k-(ET)2Cu2(CN)3 [361], The strain along the c-axis corresponds to decrease ijt left side), while the stress along the h-axis increases tljt right side)...

Fig. 20. Effect of an uniaxial pressure on the relative magnetic Bragg peak intensities associated with the three equivalent k-vectors for UN, UAs and USb single crystals. The uniaxial pressure is applied along the (001) direction. Full circles correspond to magnetic peaks Ii, associated with a wave vector perpendicular to the stress and open circles to magnetic peaks I, associated to a wave vector parallel to the stress. (Rossat-Mignod et al. )...

In hot pressing, powder mixtures of Si3N4 with additives are heated to high temperatures under an applied uniaxial pressure. Traditional hot pressing uses 20-30 MPa pressure which enhances both rearrangement of particles and grain boundary diffusion. The hot pressing offers the ability to fabricate dense products, but also limits the products to simple shapes.25... 

It should be observed, that the comparison of the "fatigue strength" reduction is different for the probes stress amplitudes for the uniaxial, pressure amplitudes for the pipe specimen. 

For these experiments, some of which were also conducted on the ILL D17 small-angle diffractometer, crystals of n-butylammonium vermiculite exhibiting the fewest obvious structural defects were selected and trimmed to a rectangular cross section with a razor blade. This enabled the surface area, and therefore the applied pressure, to be measured accurately. The samples were then immersed in a dilute solution of n-butylammonium chloride of the desired concentration and allowed to swell freely. After equilibration for at least two days at 7°C, the swollen (or colloidal) gel phase samples were placed into the uniaxial pressure cell shown in Figure 3.1. 

FIGURE 3.1 The uniaxial pressure cell apparatus used in the neutron-scattering experiments. The whole apparatus is 10 cm high. 

We now wish to examine how the structure of the dressed macroion, as determined by our diffuse neutron scattering experiments, varies with applied uniaxial stress. The best data was obtained at c = 0.03 M, with r < 0.01, when the uniaxial pressure p was varied between 0 and 0.2 atm a single experiment conducted over two days on D16 gave clear ripples at different applied stresses, as described below. As in the experiments at c = 0.1 and 0.01 M described above, T and P were held constant at 10°C and 1 atm, respectively. The details of the experiment and the small-angle patterns observed are given in reference [4], Here we concentrate on how applied uniaxial pressure affects the higher g-rangc of the structure factors. 

Given the volume fraction of the polymer inside the gel, we are now able to propose a quantitative model of bridging flocculation. Because Crawford et al. [4] studied the contraction of the interlayer spacing as a function of uniaxial stress for the same system without any added polymer, we are able to convert the observed d-values to effective uniaxial pressures caused by the bridging polymers. If we assume that we have one polymer bridge when the end-to-end polymer distance l (calculated according to Equation 12.1) exactly matches the d-value with the... 

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