Scholarlink

<p>We have synthesized three groups of Tl-based cuprate superconductors. The general composition of first group is (Cu₀.₅Tl₀.₅)(Ba₂₋ₓCaₓ)(Mg<sub>y</sub>Zn<sub>z</sub>)Cu₂O₈₋<sub>δ</sub>, where x = 0 to 2 (Ba/Ca substitution at the A-site) and y, z denote the fractional Mg/Zn occupancy in the reservoir layer, second group has (Cu₀.₅Tl₀.₅)Ba₂MCu₂O₈₋<sub>δ</sub>, where M = Be or Mg, represents substitution Ca with M atoms and third group has (Cu₀.₅Tl₀.₅)(A₂₋ₓBₓ)(Mg<sub>y</sub>Zn<sub>z</sub>)Cu₂O₈₋<sub>δ</sub>, where A = Sr or Ca, B = Ca or Mg, x = 0 to 2, and y, z denote the fractional Mg/Zn occupancy. Their structural and superconducting properties were investigated using X-ray diffraction (XRD), temperature dependent resistivity, Fourier transform infrared (FTIR) absorption. All compounds crystallize in the orthorhombic phase, exhibiting varying degrees of c-axis suppression and reduced unit cell volumes. For the studies of intrinsic mechanism of superconductivity in CuTl-1212 superconductors the thickness of the charge reservoir layer and inter-plane distance is decreased by doping Ca &amp; Sr at the Ba sites and Mg &amp; Be at the Ca sites. For such studies three groups of samples were studied, in which the first group of samples were superconducting, second group were metallic whereas in the third group the samples have shown semiconducting behavior. The Superconducting (Cu<sub>0.5</sub>Tl<sub>0.5</sub>)Ba<sub>2</sub>CaCu<sub>2</sub>O<sub>8−δ,</sub> (Cu<sub>0.5</sub>Tl<sub>0.5</sub>)(BaCa)(Mg<sub>0.5</sub>Ca<sub>0.5</sub>)Cu<sub>2</sub>O<sub>8−δ,</sub> Cu<sub>0.5</sub>Tl<sub>0.5</sub>)(BaCa)(Mg)Cu<sub>2</sub>O<sub>8−δ,</sub> (Cu<sub>0.5</sub>Tl<sub>0.5</sub>)(BaCa)Mg Zn<sub>2</sub>O<sub>8−δ</sub> samples of the first group have shown metallic variations of resistivity from room temperature down to onset of superconductivity the critical temperature of final compound suppresses in doped samples. In such doped samples Cu(1)-O<sub>A</sub>-Cu(2) and CuO<sub>2</sub> planar oxygen modes are hardened that most likely arises from the suppression in c-axes lengths and volumes of the unit cell. Excess conductivity analysis indicated that parameters such as the coherence length along the c-axis (ξc(0)), interlayer coupling (J), Fermi velocity (v<sub>F</sub>), and carrier phase relaxation time (τ<sub>φ</sub>) exhibited negligible variation with doping, suggesting that the carrier Fermi vector (k<sub>F</sub> = [3π²N/V]¹/²) remained nearly unchanged. On the other hand (Cu<sub>0.5</sub>Tl<sub>0.5</sub>)Ba<sub>2</sub>MgCu<sub>2</sub>O<sub>8−δ</sub> and (Cu<sub>0.5</sub>Tl<sub>0.5</sub>)(SrCa)MgCu<sub>2</sub>O<sub>8−δ,</sub> samples have shown metallic variations of resistivity but no sign of superconductivity down to 78&#xa0;K whereas (Cu<sub>0.5</sub>Tl<sub>0.5</sub>)Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>8−δ,</sub> (Cu<sub>0.5</sub>Tl<sub>0.5</sub>)Sr<sub>2</sub>MgCu<sub>2</sub>O<sub>8−δ,</sub> (Cu<sub>0.5</sub>Tl<sub>0.5</sub>)(SrCa)(Mg)Zn<sub>2</sub>O<sub>8−δ,</sub>(Cu<sub>0.5</sub>Tl<sub>0.5</sub>)Ca<sub>2</sub>MgCu<sub>2</sub>O<sub>8−δ</sub>, (Cu<sub>0.5</sub>Tl<sub>0.5</sub>)Ba<sub>2</sub>BeCu<sub>2</sub>O<sub>8−δ</sub> samples have shown all the way Mott variable range hopping (VRH) assisted by thermally hopping conductivity of charge carriers. In the former batch of the oxygen related phonon modes of type Tl-O<sub>A</sub>-Cu(2) and Cu(1)-O<sub>A</sub>-Cu(2) and CuO<sub>2</sub> planar oxygen modes significantly softened in comparison with un-doped (Cu<sub>0.5</sub>Tl<sub>0.5</sub>)Ba<sub>2</sub>CaCu<sub>2</sub>O<sub>8−δ</sub> whereas in (Cu<sub>0.5</sub>Tl<sub>0.5</sub>)Sr<sub>2</sub>MgCu<sub>2</sub>O<sub>8−δ,</sub> (Cu<sub>0.5</sub>Tl<sub>0.5</sub>)(SrCa)(Mg)Zn<sub>2</sub>O<sub>8−δ,</sub> (Cu<sub>0.5</sub>Tl<sub>0.5</sub>)Ca<sub>2</sub>MgCu<sub>2</sub>O<sub>8−δ</sub>, (Cu<sub>0.5</sub>Tl<sub>0.5</sub>)Ba<sub>2</sub>BeCu<sub>2</sub>O<sub>8−δ</sub> samples these phonon modes are hardened (i.e. in comparison with un-doped (Cu<sub>0.5</sub>Tl<sub>0.5</sub>)Ba<sub>2</sub>CaCu<sub>2</sub>O<sub>8−δ</sub>. These findings demonstrate that excessive suppression of the charge reservoir thickness and interlayer distance leads to the complete loss of superconductivity, highlighting the critical role of specific phonon modes and the presence of Cu³⁺ (3d⁹) ions in the CuO₂ planes for the mechanism of high-temperature superconductivity in CuTl-1212 compounds.</p>

错误：搜索内容不能为空，请输入英文关键词
错误：关键词超出字数限制，请精简
高级检索

Influence of Mg, Be, Sr, and Zn Substitution on Structure, Phonon Modes, and Superconductivity in CuTl-1212 Cuprates

  • 期刊论文

  • 发表日期：

    2026年1月30日

查看全文
  • Sadia Firdaus Akhtar,
  • Mishal Maqbool,
  • Nawazish A. Khan,
  • Syed Hamza Safeer

摘要

We have synthesized three groups of Tl-based cuprate superconductors. The general composition of first group is (Cu₀.₅Tl₀.₅)(Ba₂₋ₓCaₓ)(MgyZnz)Cu₂O₈₋δ, where x = 0 to 2 (Ba/Ca substitution at the A-site) and y, z denote the fractional Mg/Zn occupancy in the reservoir layer, second group has (Cu₀.₅Tl₀.₅)Ba₂MCu₂O₈₋δ, where M = Be or Mg, represents substitution Ca with M atoms and third group has (Cu₀.₅Tl₀.₅)(A₂₋ₓBₓ)(MgyZnz)Cu₂O₈₋δ, where A = Sr or Ca, B = Ca or Mg, x = 0 to 2, and y, z denote the fractional Mg/Zn occupancy. Their structural and superconducting properties were investigated using X-ray diffraction (XRD), temperature dependent resistivity, Fourier transform infrared (FTIR) absorption. All compounds crystallize in the orthorhombic phase, exhibiting varying degrees of c-axis suppression and reduced unit cell volumes. For the studies of intrinsic mechanism of superconductivity in CuTl-1212 superconductors the thickness of the charge reservoir layer and inter-plane distance is decreased by doping Ca & Sr at the Ba sites and Mg & Be at the Ca sites. For such studies three groups of samples were studied, in which the first group of samples were superconducting, second group were metallic whereas in the third group the samples have shown semiconducting behavior. The Superconducting (Cu0.5Tl0.5)Ba2CaCu2O8−δ, (Cu0.5Tl0.5)(BaCa)(Mg0.5Ca0.5)Cu2O8−δ, Cu0.5Tl0.5)(BaCa)(Mg)Cu2O8−δ, (Cu0.5Tl0.5)(BaCa)Mg Zn2O8−δ samples of the first group have shown metallic variations of resistivity from room temperature down to onset of superconductivity the critical temperature of final compound suppresses in doped samples. In such doped samples Cu(1)-OA-Cu(2) and CuO2 planar oxygen modes are hardened that most likely arises from the suppression in c-axes lengths and volumes of the unit cell. Excess conductivity analysis indicated that parameters such as the coherence length along the c-axis (ξc(0)), interlayer coupling (J), Fermi velocity (vF), and carrier phase relaxation time (τφ) exhibited negligible variation with doping, suggesting that the carrier Fermi vector (kF = [3π²N/V]¹/²) remained nearly unchanged. On the other hand (Cu0.5Tl0.5)Ba2MgCu2O8−δ and (Cu0.5Tl0.5)(SrCa)MgCu2O8−δ, samples have shown metallic variations of resistivity but no sign of superconductivity down to 78 K whereas (Cu0.5Tl0.5)Sr2CaCu2O8−δ, (Cu0.5Tl0.5)Sr2MgCu2O8−δ, (Cu0.5Tl0.5)(SrCa)(Mg)Zn2O8−δ,(Cu0.5Tl0.5)Ca2MgCu2O8−δ, (Cu0.5Tl0.5)Ba2BeCu2O8−δ samples have shown all the way Mott variable range hopping (VRH) assisted by thermally hopping conductivity of charge carriers. In the former batch of the oxygen related phonon modes of type Tl-OA-Cu(2) and Cu(1)-OA-Cu(2) and CuO2 planar oxygen modes significantly softened in comparison with un-doped (Cu0.5Tl0.5)Ba2CaCu2O8−δ whereas in (Cu0.5Tl0.5)Sr2MgCu2O8−δ, (Cu0.5Tl0.5)(SrCa)(Mg)Zn2O8−δ, (Cu0.5Tl0.5)Ca2MgCu2O8−δ, (Cu0.5Tl0.5)Ba2BeCu2O8−δ samples these phonon modes are hardened (i.e. in comparison with un-doped (Cu0.5Tl0.5)Ba2CaCu2O8−δ. These findings demonstrate that excessive suppression of the charge reservoir thickness and interlayer distance leads to the complete loss of superconductivity, highlighting the critical role of specific phonon modes and the presence of Cu³⁺ (3d⁹) ions in the CuO₂ planes for the mechanism of high-temperature superconductivity in CuTl-1212 compounds.