Effect of pressure on Raman modes in MBa2Cu3O7-type materials

doi:10.1016/0921-4534(88)90584-9

Physica C: Superconductivity

Volumes 153–155, Part 1, June 1988, Pages 264-265

https://doi.org/10.1016/0921-4534(88)90584-9 Get rights and content

Abstract

The effect of pressure on Raman modes of ceramic superconducting samples of MBa₂Cu₃O_7−x (M = Y, Eu) has been investigated up to 16 GPa at 300 K. Linear pressure coefficients are reported for the strongest modes at around 145, 300–340, 440, and 500 cm⁻¹. All these modes exhibit an increase in frequency, with average mode Grüneisen pameters falling in the range from 1.2 to 2.2. The pressure dependence of the mode frequencies is calculated within the framework of a shell model, which has recently been used to aid the mode assignment. Calculated mode Grüneisen parameters are found to be in satisfactory agreement with experiment if the proper volume dependence of the polarizability is taken into account.

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Cited by (39)

Predictions for structural stability and electronic evolution in pressure-induced overdoped YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7</inf>
2018, Computational Materials Science
Citation Excerpt :
Nonetheless, the span of 40 GPa is well reflected, except for slight deviations from the results at 0 GPa, which is consistent with Syassen et al. [44]. Experimentally, Syassen et al. [44] have revealed that the pressure effect on the frequencies of the three oxygen modes is characterized by positive linear pressure coefficients dω/dP, which are constant over a wide range of pressure up to 12 GPa. In this work, for the O(4) mode, this quantity was found to be 5.5 cm−1/GPa (5.5 cm−1/GPa) at 0–20 GPa, and 4.2 cm−1/GPa at 20–40 GPa.
The electronic evolution in the entire overdoped region of cuprates has never been accessed, though the clarification of this evolution should help to refine the crucial physical arguments in producing the superconductivity. Motivated by uncovering this, we performed first-principles calculations and molecular dynamics simulations for the pressure-induced overdoped YBa₂Cu₃O₇. The mechanical and dynamic stability of orthorhombic YBa₂Cu₃O₇ lays the foundation of exploration for the electronic evolution. We found that no transition of semiconducting state was identified and similar Fermi surfaces still exist in the entire overdoped region. The role of charge density at CuO₂ plane was also discussed. Moreover, based on the analysis of BCS picture, we recommended that the electron-phonon regime is not prominently responsible for the T_c, and the evolution of N(E_F) or the position of Van Hove singularity (VHs), i.e., E_F-E_VHs, may direct an alternative way instead to uncover the superconductivity of YBa₂Cu₃O₇ category if the BCS picture is taken.
Non-linear lattice response of Sm oxypnictides to hydrostatic pressure
2013, Journal of Physics and Chemistry of Solids
Citation Excerpt :
Similar values for the Grüneisen parameters have been obtained for YBa2Cu3Ox cuprates (Ref. [26], which agrees with the average pressure dependence of our data presented in Ref. [22]). Although the original high pressure study of Ref. [26] has not revealed any phonon anomalies, our more recent studies had clearly shown that the strong Ag phonons follow a non-linear pressure dependence [22], similar to the one observed in this work. It therefore appears that in pnictides as in cuprates intrinsic lattice instability may exist related with the variation of the carrier concentration.
Hydrostatic pressure Raman measurements at room temperature have been carried out on the SmFeAsO (Sm1111) series of oxypnictides with various substitutions (F for O and Co for Fe) and transition temperature in order to investigate lattice modifications and their connection to doping and superconductivity. Synchrotron XRD data on some of these compounds indicated that at low doping the lattice constants vary smoothly with pressure, but with further increasing of the carrier concentration there is a deviation from the normal equation of state and these effects are related with modifications in the superconducting FeAs₄ tetrahedra. The hydrostatic pressure Raman measurements indicate that the A_1g mode of the rare earth atom for the superconducting compounds deviates from the linear pressure dependence at the same pressures where the XRD results show pressure-induced lattice anomalies. A similar anomaly is found for the As phonon of the same symmetry. As in cuprates, the effect is diminished in the non-superconducting compounds and it is not related with the F substitution being present in the Sm(Fe_1−xCo_x)AsO as well. The calculated Grüneisen parameters indicate a more anharmonic phonon for the Fe atom compared with the Sm and As atoms.
A Raman view of local lattice distortions and charge transfer in cuprates
2006, Journal of Physics and Chemistry of Solids
Small changes in doping or the application of a hydrostatic pressure can induce non-linear lattice distortions, lattice instabilities, and phase separation in the cuprates. In YBa₂Cu₃O_x, oxygen doping above optimal induces a separation into microphases originating from a modification in the buckling of the CuO₂ planes. In the same compound, the excess nominal doping by Ca creates changes in the CuO₂ buckling at some critical concentrations. These are correlated with the formation of domains where the additional carriers brought by Ca remain isolated surrounded by yttrium atoms. Furthermore, it was observed that hydrostatic pressure induces non-linear modifications in the spectral characteristics of the A_g-symmetry phonons in all cuprates studied (YBa₂Cu₃O_6.5, YBa₂Cu₃O_over, YBa₂Cu₄O₈, and Bi₂Sr₂CaCu₂O₈). A coexistence of phases appears at a critical pressure where changes in the superconducting transition temperature have been detected. We have also observed similar correlations between the transition temperature and spectral modifications by chemical doping in the Raman spectra of La₂₋_xSr_xCuO₄. Finally, soft modes were found in the cuprates studied, with energies scaling with the maximum transition temperature of the compound.
Pressure-induced effects in high-T<inf>c</inf> superconductors: Raman scattering as a probe of charge-lattice dynamics under high pressure
2001, Physica C: Superconductivity and its Applications
The Raman spectra of Bi₂Sr₂CaCu₂O_8+d (Bi2212) and YBa₂Cu₄O₈ (Y124) have been investigated as a function of hydrostatic pressure. In both the overdoped Bi2212 and the underdoped Y124, the 140 cm⁻¹ Cu mode exhibits a pronounced nonlinear pressure dependence which correlates to the dependence of T_c versus pressure. We argue that this behavior is a signature of charge-redistribution effects induced by compression. For Bi2212, we also find that the mode-specific Grüneisen parameters scale inversely with the corresponding phonon frequencies, a behavior which is reminiscent of phonon pressure dependences in molecular solids.
High-pressure Raman study of Bi<inf>2</inf>Sr<inf>2</inf>CaCu<inf>2</inf>O<inf>8+d</inf>: indications of strong bond-strength hierarchy and pressure-induced charge transfer
2000, Physica C: Superconductivity and its Applications
Phonon Raman scattering from slightly overdoped Bi₂Sr₂CaCu₂O_8+d (Bi2212) samples have been investigated under hydrostatic pressure up to 7.2 GPa. The mode-specific Grüneisen parameters scale inversely with the corresponding phonon frequencies, the behavior of which is reminiscent of phonon pressure dependences in molecular solids. We also find that the 140 cm⁻¹Cu mode exhibits a pronounced nonlinear pressure dependence which correlates to the dependence of T_c versus pressure. The data are interpreted in terms of a non-uniform structural compressibility that results in a redistribution of charge carriers within the Bi2212 unit-cell.
Phase separation in Ca substituted YBCO
2000, Physica C: Superconductivity and its Applications
A room temperature micro-Raman spectroscopic study at hydrostatic pressures up to 4GPa has been carried out on Y_1−xCa_xBa₂Cu₃O_7−δ polycrystalline superconducting compounds with x = 0.00–0.20 and δ = 0.045-0.005. Apart from the five strong Raman active phonons (4A_g + 1B_1g-like), additional structures have been observed in the y(cc) $y$ (402 cm⁻¹) and the y(xx) $y$ (300 and 322 cm⁻¹) scattering configurations with increasing intensities with the Ca content. The modes that appear in the out-of-phase B_1g phonon of O_pl are related to the disorder introduced by the Ca substitution for Y and to a local mode induced by the Ca atoms. The variation, with x, of the relative intensities of the constituent peaks of the O_pl in-phase phonon indicates that this phonon behavior depends on the amount of oxygen and not the concentration of the Ca substitution introduced carriers. There seem to exist two oxygen content differentiated phases which are present also in the pure oxygen overdoped YBCO. The insensitivity of the O_pl in-phase mode frequency combined with the behavior of the O_apex phonon, can be attributed to the excess charge distribution away from the CuO₂ planes. A phase separation seems to be induced for hydrostatic pressures above 3GPa possibly related to the Ca atom cluster formation.

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Effect of pressure on Raman modes in MBa2Cu3O7-type materials

Abstract

Solid State Commun.

Effect of pressure on Raman modes in MBa₂Cu₃O₇-type materials