Structural investigation of high-Tc superconductor EuBa2Cu3Oy by microRaman spectroscopy

Structural and spectroscopic evidence for stable chemical bonds and the correlation with highTcsuperconductivity

“…The 390 cm −1 mode and 575 cm −1 modes are quite broad and their intensities increase dramatically with the addition of La, and thus could be attributed to IR modes which become Raman active through the loss of local inversion symmetry associated with the increased doping level [27,28]. The weak 190 cm −1 mode is not usually seen in the Raman spectra of the Y123 system, however, it was reported once by Burns [29] and no assignment has been given so far.…”

Structural and superconducting properties of EuBa2Cu3O7 xthin films grown by off-axis pulsed laser deposition

“…Finally, the frequency shift of the O(4)-A g mode is currently used to estimate the oxygen content x of Y123 material: the Raman frequency spans from 463 cm −1 (x = 1) to 503 cm −1 (x = 0) [26]. For Eu123 films [22] we observe this mode at higher frequency (∼505-510 cm −1 ). The measured frequency values indicate that there was no large oxygen inhomogeneity across the films: only in Eu123-1 are there regions where the oxygen content is slightly lower than the average value (503 cm −1 rather than 507 cm −1 ).…”

“…Additional modes are observed around 223 and 600 cm −1 . The former peak may be due to a particular order of oxygen ions in the basal plane of the structure leading to a higher number of holes in the CuO 2 planes and a higher T c [22]. The 600 cm −1 peak may be associated with a disorder-induced band, related to oxygen vacancies [22] in Cu(1)-O(4) chains along the b axis; such a peak may also be attributed to the Ba 2 Cu 3 O 5.9 cuprate [23].…”

“…The former peak may be due to a particular order of oxygen ions in the basal plane of the structure leading to a higher number of holes in the CuO 2 planes and a higher T c [22]. The 600 cm −1 peak may be associated with a disorder-induced band, related to oxygen vacancies [22] in Cu(1)-O(4) chains along the b axis; such a peak may also be attributed to the Ba 2 Cu 3 O 5.9 cuprate [23]. Comparing peak frequency values of Eu123 films to those obtained for Y123, a hardening of the modes associated with the vibrations along the c-axis is generally observed: the Eu larger ionic radius makes the c-direction bonds shorter and the frequency of the stretching vibrations increases due to anharmonicities [22], thus the O(4)-A g mode is observed at values (505-510 cm −1 ) larger than Y123 ones.…”

“…The 600 cm −1 peak may be associated with a disorder-induced band, related to oxygen vacancies [22] in Cu(1)-O(4) chains along the b axis; such a peak may also be attributed to the Ba 2 Cu 3 O 5.9 cuprate [23]. Comparing peak frequency values of Eu123 films to those obtained for Y123, a hardening of the modes associated with the vibrations along the c-axis is generally observed: the Eu larger ionic radius makes the c-direction bonds shorter and the frequency of the stretching vibrations increases due to anharmonicities [22], thus the O(4)-A g mode is observed at values (505-510 cm −1 ) larger than Y123 ones. By contrast, the expansion of the CuO 2 planes induces larger nearest neighbour distances resulting in the softening of the bending modes (i.e.…”