A high temperature ${\mathrm{Cu}}_{0.5}{\mathrm{Tl}}_{0.5}{\mathrm{Ba}}_{2}{\mathrm{Ca}}_{3}{\mathrm{Cu}}_{4\ensuremath{-}y}{\mathrm{Zn}}_{y}{\mathrm{O}}_{12\ensuremath{-}\ensuremath{\delta}}$ ($y=0$, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5) superconductor with four $\mathrm{Zn}{\mathrm{O}}_{2}$ planes is synthesized, in which the zero resistivity critical temperature $[{T}_{c}(R=0)]$, the quantity of diamagnetism, and critical current density $({J}_{c})$ are found to increase with enhanced Zn doping. From the x-ray diffraction studies, the $c$-axis lengths are found to decrease with increased Zn doping in ${\mathrm{Cu}}_{0.5}{\mathrm{Tl}}_{0.5}{\mathrm{Ba}}_{2}{\mathrm{Ca}}_{3}({\mathrm{Cu}}_{4\ensuremath{-}y}{\mathrm{Zn}}_{y}){\mathrm{O}}_{12\ensuremath{-}\ensuremath{\delta}}$. The softening of apical oxygen modes observed in Fourier transform infrared absorption measurements has shown that the decreased $c$-axis length is among $\mathrm{Cu}{\mathrm{O}}_{2}∕\mathrm{Zn}{\mathrm{O}}_{2}$ planes. The decreased $c$-axis length increases the Fermi vector ${k}_{F}$, the coherence length ${\ensuremath{\xi}}_{c}$, and the superconductivity order parameter, which result into enhanced superconducting properties. The superconducting properties in these compounds were further enhanced by optimizing the carriers in $\mathrm{Cu}{\mathrm{O}}_{2}∕\mathrm{Zn}{\mathrm{O}}_{2}$ planes. The optimum numbers of carriers in these compounds were achieved by postannealing the samples in oxygen atmosphere.

Absence of a pair-breaking mechanism in Cu 0.5 Tl 0.5 Ba 2 Ca 3 Cu 4 − y Zn y O 12 − δ

We have synthesized Cu 0.5 Tl 0.5 Ba 2 Ca 2 Cu 3− y Ni y O 10− δ ( y  = 0, 0.5, 1.0, 1.5) superconductors at normal pressure and studied the enhanced correlation among CuO 2 /NiO 2 planes of Cu 0.5 Tl 0.5 Ba 2 Ca 2− y Mg y Cu 1.5 Ni 1.5 O 10− δ ( y  = 0.5, 1.0, 1.5) superconductors by doping Mg at the Ca sites. Surprisingly, we have not observed any substantial depression of critical temperature with Ni doping in Cu 0.5 Tl 0.5 Ba 2 Ca 2 Cu 3− y Ni y O 10− δ ( y  = 0, 0.5, 1.0, 1.5) superconductors. The main objective of Mg substitution is to enhance the inter-plane coupling which may increase the interactions of the spins of Ni atoms in different planes. The increased inter-plane coupling may enhance interactions of the atomic spins with the free carriers and might be a key to understanding the effects of spin scattering and their role in the mechanism of high temperature superconductivity. We have observed a decrease of c -axis length with increased Mg concentration in Cu 0.5 Tl 0.5 Ba 2 Ca 2− y Mg y Cu 1.5 Ni 1.5 O 10− δ ( y  = 0.5, 1.0, 1.5) superconductors, showing an enhanced inter-plane coupling. The room temperature resistivity of the samples is decreased and the zero resistivity critical temperature [ T c ( R  = 0)] and the magnitude of diamagnetism are increased with higher Mg doping in Cu 0.5 Tl 0.5 Ba 2 Ca 2− y Mg y Cu 1.5 Ni 1.5 O 10− δ superconductors. A maximum diamagnetism is observed in the samples when Mg atoms replace 75% of the Ca atoms, which shows that a higher Mg doping concentration enhances the inter-plane coupling which possibly promotes the de-localization of the carriers to the Ni 2+ sites and results in enhanced superconducting properties.

Magnetic ion doped Cu1- xTlxBa2Ca2- yMgyCu1.5Ni1.5O10- δ (y = 0, 0.5, 1.0, 1.5) superconductors and their improved inter-plane coupling

Suppression of anti-ferromagnetism by enhanced solubility of Ni in Cu1−xTlxBa2Ca2Cu3−yNiyO10−δ (y = 0, 0.5, 1.0, 1.5) superconductor

The phonon modes and superconducting properties of Cu0.5Tl0.5Ba2Ca2Cu3?yZnyO10?? (y = 0, 1.5, 2.5) have been investigated. To optimize the carriers in the unit cell, annealing experiments were performed at different temperatures and for different annealing times. The resistivity and ac-susceptibility measurements revealed that the samples become optimally doped when they were annealed at 500??C for 6?h. The optimum concentration of carriers in the conducting ZnO2/CuO2 planes gives the desired Fermi velocity VF that is necessary for enhanced superconductivity. The volume of the unit cell observed through x-ray diffraction scans is found to decrease with the increase of Zn doping, promoting an increase in the Fermi vector KF and effective density of states which results in enhanced superconductivity parameters. These annealing experiments manifested the importance of the apical oxygen modes of type Cu(1)?OA?M(2) and Tl?OA?M(2) and the CuO2 planar mode M(2)?Op?M(2) (where M = Zn/Cu) for superconductivity. The Fourier transform infrared (FTIR) absorption studies are consistent with the resistivity and ac-susceptibility measurements.

Studies of the phonon modes and superconducting properties of Cu0.5Tl0.5Ba2Ca2Cu3−yZnyO10−δ (y = 0, 1.5, 2.5)

Synthesis structure and superconductivity in all-perovskite-layered titanium cuprates

The effect of substitution at the Cu site by the transition elements Fe, Co, Ni, and Zn on the structure and superconducting properties of ${\mathrm{NdBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ has been investigated. Compared to the ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3\mathrm{\ensuremath{-}}\mathit{x}}$${\mathit{M}}_{\mathit{x}}$${\mathrm{O}}_{7+\mathrm{\ensuremath{\delta}}}$ (M=Fe, Co, Ni, Zn) system, considerably high solid solubility and drastic ${\mathit{T}}_{\mathit{c}}$ suppression is achieved in the Nd 1:2:3 system. The maximum solid solubilities achieved for the dopants are x=1.0 for M=Fe and Co and x=0.8 for M=Ni and Zn. An orthorhombic-to-tetragonal (O\ensuremath{\rightarrow}T) transition is observed at x=0.08 for M=Fe, Co similar to the case of the M-doped Y 1:2:3 system. However, a second T\ensuremath{\rightarrow}O transition is observed in Nd 1:2:3 at x=0.5 for M=Co and x=0.8 for M=Fe. For the Ni- and Zn-doped phases, an O\ensuremath{\rightarrow}T transition is observed at x=0.4 for M=Ni and x=0.5 for M=Zn. The doped phases are superconducting up to x=0.2 (M=Fe, Co, Ni) and x=0.08 (M=Zn). The initial rate of ${\mathit{T}}_{\mathit{c}}$ suppression (up to 3.33 at. %) is \ensuremath{\sim}14 K/at. % for M=Fe, Co, and Ni and \ensuremath{\sim}28 K/at. % for M=Zn and is much higher than that reported for the Y 1:2:3 system. The Fe- and Zn-doped phases, heated in flowing ${\mathrm{N}}_{2}$ gas at 800 \ifmmode^\circ\else\textdegree\fi{}C followed by reoxygenation at 450 \ifmmode^\circ\else\textdegree\fi{}C show higher ${\mathit{T}}_{\mathit{c}}$ and sharper superconducting transition. Hole doping by Ca substitution (y) at the Nd site in the Zn-doped (x=0.1) semimetallic-semiconducting Nd 1:2:3 phase induces metallicity and superconductivity for y\ensuremath{\ge}0.1 and a ${\mathit{T}}_{\mathit{c}}$ of 32 K is obtained for y=0.2.

Influence of Cu-site substitution on the structure and superconducting properties of the NdBa2Cu3-xMxO7+ delta (M=Fe,Co) and NdBa2Cu3-xMxO7- delta (M=Ni,Zn) systems.

Structure and physical properties of the LnBa2Cu2MO7+δ system (Ln = rare earth and Y;M = Ga, Co)

We investigated the structural, thermodynamic, and optoelectronic properties of InxAl1−xN, InxGa1−xN, and GaxAl1−xN alloys for x = 0.25, 0.50 and 0.75. The optimized lattice constants showed nearly a small deviation trend from Vegard’s law with composition x. The impact of mutual alloying is evaluated in terms of enthalpy and interaction parameters. The calculated electronic band structures and density of states lie in the bandgap ranges from 1.09 eV to 2.72 eV for composition x 0.25 to 0.75. These electronic properties suggested that alloys are suitable bandgap semiconductors with large variations in their bandgap energies for optoelectronic applications. The optical properties are calculated using the dielectric constant and correlated with the calculated electronic band structures. The main reflectivity peak and absorption coefficient showed a significant shift with increasing x. These monolayers’ suitable bandgap and optoelectronic properties make them attractive for optoelectronic applications, including photovoltaics and photodetectors.

N. R. S. Kumar

Papers

Influence of Cu-site substitution on the structure and superconducting properties of the NdBa2Cu3-xMxO7+ delta (M=Fe,Co) and NdBa2Cu3-xMxO7- delta (M=Ni,Zn) systems.

Structure and physical properties of the LnBa2Cu2MO7+δ system (Ln = rare earth and Y;M = Ga, Co)

Bandgap engineering and modulation of thermodynamic, and optical properties of III-N monolayers XN (X = In, Ga & Al) by mutual alloying