Elastic behaviour under pressure of high-T _c superconductors RBa₂Cu₃O_7-x (R = Y, Gd and Eu)

Pressure, Temperature and Concentration Dependences of Phonon Frequency with Variable Gr�neisen Parameter: Fits to the Raman-Active Eg Mode in TiO2 and Ti1?xZrxO2 (x ? 0.1)

“…It is remarkable that all the data are within these limits and the nonlinear change is assured. While the Gru È neisen parameter of YBa 2 Cu 3 O x is controversial with respect to its size [30,31], the value of g 0 2X7 at 300 K for YBa 2 Cu 3 O x [32] was appointed for the A g mode at %500 cm À1 . It should be recalled that e 0 ensures linearity between the frequency and x, but the x dependent Gru È neisen parameter is invoked to reproduce the data that could change nonlinearly.…”

Ultrasonic determination of the elastic moduli and their pressure dependences in very dense YBa{sub 2}Cu{sub 3}O{sub 7{minus}x}

“…The saml_le \-density, determined by Archimedes' principle using acetone as the floatation liquid, was 6_70kgm 3 which is 95.8% of the X-ray densit_so its mean porosity n is 0.042. This material is su_.stantially denser than any YBa2Cu307._ ceramic whose ultrasonic velocities have been determined as a function of temperature and \ pressure; the densest sample previously examined had a porosity of 0.056 [ 1,2] less than about 30itm.…”

“…x [1][2][3] (and other related cuprates, including GdBa2Cu_OT.xin both its orthorhombic and tetragonal forms [4,5], Bi2Sr_Ca_tCu, O4+2,(with n=2 and 3) [6] and Lal.xSr0.2CuO4 [3]) is much smaller than that B r(p) determined [7][8][9][10][11][12] at very high pressures from x-ray measurements of lattice parameters in a diamond cell. This difference has been ascribed [1][2][3][4][5][6] to the large magnitude of (OB/OP)e--o determined from the effects of hydrostatic pressure on ultrasonic wave velocity.…”

“…x [1][2][3] (and other related cuprates, including GdBa2Cu_OT.xin both its orthorhombic and tetragonal forms [4,5], Bi2Sr_Ca_tCu, O4+2,(with n=2 and 3) [6] and Lal.xSr0.2CuO4 [3]) is much smaller than that B r(p) determined [7][8][9][10][11][12] at very high pressures from x-ray measurements of lattice parameters in a diamond cell. This difference has been ascribed [1][2][3][4][5][6] to the large magnitude of (OB/OP)e--o determined from the effects of hydrostatic pressure on ultrasonic wave velocity. A recent reanalysis [ 13] of the high pressure x-ray [7][8][9][10][11][12] and neutron [14][15][16] diffraction data has led to a substantial reduction of Br(p) and a large increase in the value of its pressure derivative (igB/OP): both trending towards the ultrasonic values and conf'm'rfing the earlier observation [1,2] of the highly pressure dependent nature of the bulk modulus at moderate pressures.…”

“…This difference has been ascribed [1][2][3][4][5][6] to the large magnitude of (OB/OP)e--o determined from the effects of hydrostatic pressure on ultrasonic wave velocity. A recent reanalysis [ 13] of the high pressure x-ray [7][8][9][10][11][12] and neutron [14][15][16] diffraction data has led to a substantial reduction of Br(p) and a large increase in the value of its pressure derivative (igB/OP): both trending towards the ultrasonic values and conf'm'rfing the earlier observation [1,2] of the highly pressure dependent nature of the bulk modulus at moderate pressures. Hence the question as to whether the true bulk modulus of YBa2Cu3OT._is the smaller ultrasonic value at atmospheric pressure or the much larger one obtained from high pressure lattice parameter data has to some extent been resolved in favour of the former.…”