Raman spectroscopy is an excellent analytical tool for investigating phonon vibrational modes in the family of cuprate compounds known as RBa₂Cu₃O₇−δ, where R represents a rare earth element. Within this family, two particularly notable members are the high-temperature superconductor YBa₂Cu₃O₇−δ (YBCO) and the cuprate insulator PrBa₂Cu₃O₇−δ (PBCO). In this study, we conducted Raman spectroscopy measurement on (110)-oriented PBCO thin film and on Ga, Al, Fe, Co, Ni, and Zn ions-doped (110)-oriented PBCO thin films to compare their phonon vibrational modes and assess the impact of ion doping. The Raman spectrum of the (110)-oriented PBCO sample displayed four prominent Ag-type modes at approximately 130 cm⁻¹, 150 cm⁻¹, 440 cm⁻¹, and 520 cm⁻¹. These modes correspond to the vibrations of Ba, Cu (2), in-phase O (2) – O (3), and the apical oxygen O (4), respectively. We observed that the Raman mode of undoped PBCO at around 520 cm⁻¹ softened in the Ga, Al, Fe, and Co-doped PBCO thin films, while it remained unaffected in the Zn and Ni-doped thin films. We attributed these results to changes in the Cu (1) – O (4) and Cu (2) – O (4) bond lengths after the partial substitution of Cu. Additionally, a new Raman mode appeared near 610 cm⁻¹ in the spectra of Ga, Al, Fe, and Co-doped PBCO thin films. This mode, which is infrared (IR) active, became Raman-active when the symmetry of the unit cell was broken at the Cu-O chain site due to the partial substitution of Cu (1) ions by the dopants. Furthermore, the "O (2) – O (3) in-phase Raman mode" near 440 cm⁻¹ remained unaffected in the Fe, Co, Ga, and Al-doped PBCO thin films but softened in the Zn and Ni-doped PBCO thin films. Our findings suggest that these metal ions selectively replace Cu (2) and Cu (1) ions within the PBCO unit cell, leading to changes in some Raman and infrared-active modes. Divalent ions, such as Ni and Zn, replace Cu (2) ions from the CuO₂ planes, while trivalent ions like Ga, Al, Fe, and Co replace Cu (1) ions from the Cu-O chains. This latter replacement disrupts the symmetry of the PBCO unit cell and introduces local disorder at the Cu-O chain site. Moreover, these results are consistent with our electrical transport measurements, enhancing the understanding of the structural and electrical transport properties of the metal-ion-doped PBCO compounds.
Author (s) Details
Hom Kandel
Applied Physics Laboratory, University of Wisconsin-Parkside, Kenosha, WI
53144, USA and Department of Materials Science and Engineering, University of
Wisconsin-Madison, WI 53706, USA.
Milko Iliev
Texas Center for Superconductivity, University of Houston, Houston, TX,
77204, USA.
Please see the book here:- https://doi.org/10.9734/bpi/crpps/v7/2568
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