Study of (DNPs)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/CuTl-1223 Nanoparticle-Superconductor Composites

Sol-gel and solid-state reaction methods were used to synthesize diamond nanoparticles (DNPs) and (DNPs) _x /CuTl-1223 (x = 0, 0.25, 0.50, and 1.00 wt.%) nanoparticle-superconductor composites, respectively. Effects of these DNPs on structural, morphological, compositional, and transport properties of CuTl-1223 superconducting phase were investigated by different experimental techniques such as X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, scanning electron microscopy (SEM), and resistivity versus temperature (R-T) measurements. The unchanged crystal structure and stoichiometry of host CuTl-1223 superconducting matrix with addition of DNPs gave evidence about the dispersion of nanoparticles at the grain boundaries of the host matrix, which may heal up the inter-granular voids and pores resulting in enhanced inter-grain connectivity. Critical transition temperature T _c (0) and hole concentration of CuTl-1223 superconductor were observed to be increased with addition of DNPs up to a certain optimum value (i.e. x = 0.5 wt.%).     

Magneto-transport properties of (Cu)x/CuTl-1223 nanoparticles-superconductor composites

Copper (Cu) nanoparticles and Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10−δ (CuTl-1223) superconducting phase were synthesized by sol-gel and solid-state reaction, respectively. These metallic Cu nanoparticles were added in CuTl-1223 superconducting matrix to get (Cu)_x/CuTl-1223; x = 0–4.0 wt% nanoparticles-superconductor composites and their temperature dependent magneto-transport properties were studied. The zero-field-cooled (ZFC) and field-cooled (FC) temperature dependent magnetization (M-T) measurements of (Cu)_x/CuTl-1223 samples showed an increase in transition temperature and in amplitude of diamagnetic signal after the inclusion of Cu nanoparticles in the host CuTl-1223 matrix. The improvement in these magneto-transport properties can be attributed to the increase in number of efficient pinning centres in CuTl-1223 matrix after addition of Cu nanoparticles. Magnetization hysteresis (M-H) loops were obtained at various operating temperatures from which the magnetization critical current density (J_c) was estimated using Bean's critical state model. M-H loops indicated the combined superconducting and ferromagnetic behaviour up to 90 K in all (Cu)_x/CuTl-1223 samples. Improvement in J_c could also be due to increase in number of pinning centres with addition of Cu nanoparticles in CuTl-1223 matrix. Maximum improvement in magneto-transport properties of (Cu)_x/CuTl-1223 samples was observed for x = 1.0 wt%, which had specified the optimum content level of Cu nanoparticles in CuTl-1223 phase.     

Flux Pinning with Addition of Gold Nanoparticles in CuTl-1223 Superconductor

We investigated the effects of gold (Au) nanoparticles on flux pinning in Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10?δ (CuTl-1223) superconductor by infield temperature-dependent dc-resistivity measurements. The values of \(\phantom {\dot {i}\!}T_{\mathrm {c}}^{\text {onset}}\) (K) remained almost unaffected by applying external magnetic field on (Au) _x /CuTl-1223; (x = 0～1.5 wt.%) composites samples. But a decreasing trend in T _c(0) and increasing trend in resistive broadening (ΔT) by increasing external applied magnetic field were reduced after addition of Au nanoparticles in CuTl-1223 superconducting matrix. The activation energy (U _o) was calculated according to thermally activated flux flow (TAFF) model by using the Arrhenius Law. The increase in T _c(0), U _o, and upper critical field (H _c2) indicates a strong flux pinning after the inclusion of Au nanoparticles and found optimum for x = 1.0 wt.%.     

Tuning of Dielectric Parameters of (NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/CuTl-1223 Nano-superconductor Composites by Temperature and Frequency

Nickel ferrite (NiFe₂O₄) nanoparticles and Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10?δ (CuTl-1223) superconductor were prepared separately and then mixed in an appropriate ratios at the final stage to obtain (NiFe₂O₄) _x /CuTl-1223 (x = 0, 0.5, and 1.0 wt%) nano-superconductor composites. There was no significant change observed in crystal structure of the host CuTl-1223 superconducting matrix after the addition of NiFe₂O₄ nanoparticles. The value of zero-resistivity critical temperature { T _{c(R = 0)} (K)} was decreased with increasing content of these nanoparticles in these composites. Maximum values of dielectric loss tangent (tanδ) at lowest possible frequency of 40 Hz were increased with the increase of operating temperature, while its values were decreased and become almost zero at higher frequencies for all these samples at all operating temperatures. A peak in dielectric loss tangent was shifted towards lower frequency values with the addition of these nanoparticles in CuTl-1223 superconducting matrix. The dielectric loss tangent peak was also shifted towards lower frequency values in all these samples with increasing operating temperature, which shows the relaxator-like behavior in these samples. The dielectric parameters of these composites can be tuned by frequency, operating temperatures, and nature and content of these nanoparticles.     

Enhanced Inter-grain Connectivity in Nano-particles Doped (Cu0.5Tl0.5)Ba2Ca2Cu3O10?δ Superconductors

Polycrystalline (Cu_0.5Tl_0.5)Ba₂Ca₂Cu₃O_10??? superconductors show strong composition variations at the termination ends of the crystals which compromise over-all superconducting properties of the final compound. These composition variations are one of the root causes of void formation which produces a poor quality material. The better inter-grain coupling suppresses the Josephson losses required for higher transport critical current density (J _c ). The lower losses across the inter-grain Josephson junctions are essential for wire and microelectronic applications. We have fixed such inadvertent composition variation in (Cu_0.5Tl_0.5)Ba₂Ca₂Cu₃O_10??? superconductors by doping them with nano-particles of CuO, BaO and CaO₂. Nano-particles doped (Cu_0.5Tl_0.5)Ba₂Ca₂Cu₃O_10??? superconductors were synthesized at 860?°C and characterized using X-ray diffraction (XRD), resistivity (??), ac-susceptibility (??), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) measurements. The magnitude of superconductivity is significantly enhanced with the doping of nano-particles. The samples with 15?wt.?% addition of CuO nano-particles have even shown textured elongated crystalline with extremely low population of voids.     

Complex Electric Modulus Spectroscopy of (MnFe<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/CuTl-1223 Nanoparticles-Superconductor Composites

Manganese ferrite (MnFe₂O₄) nanoparticles and Cu_0.5Tl₀.₅Ba₂Ca₂Cu₃O_10?δ(CuTl-1223) superconducting phase were synthesized by sol-gel and solid-state reaction methods, respectively. Different contents of MnFe₂O₄ nanoparticles were added in CuTl-1223 superconducting matrix to get (MnFe₂O₄)_x/CuTl-1223; x =? 0～2.0 wt% nanoparticles-superconductor composites. Complex electric modulus spectroscopy measurements of (MnFe₂O₄)_x/CuTl-1223 composites were carried out at different test frequencies from 20 Hz to 10 MHz and at different operating temperatures from 78 to 253 K to analyze and interpret the dynamical aspects of electrical transport phenomena (i.e., such as carrier hopping rate, conductivity, and blocking factor). The complex electric modulus spectra showed the effects of both grains and grain-boundaries on electrical properties. The capacitance of grain-boundaries was found higher than that of grains. The capacitive behavior of grains was increased and that of grain-boundaries was decreased with increasing operating temperature for all these samples. Blocking factor of these composites was increased with increasing contents of MnFe₂O₄ nanoparticles. Shifting of peaks in imaginary part of modulus spectra towards lower frequency with increasing contents of these nanoparticles showed non-Debye type relaxation phenomenon in the material.     

Fluctuation Induced Conductivity in Hg-Doped (Cu0.5Tl0.5?x Hg x )Ba2Ca3 Cu 4O12?δ Superconductor

The fluctuation induced conductivity (FIC) analysis on resistivity data of the Hg-doped (Cu_0.5Tl_0.5−x Hg _x )Ba₂Ca₃Cu₄O_12−δ (x=0, 0.15, 0.25, 0.35) superconductor has been carried out in the light of the Aslamazov–Larken (AL) theory. The superconducting properties have been improved with Hg-doping (up to x=0.25) at Tl sites in the Cu_0.5Tl_0.5Ba₂O_4−y charge reservoir layer. These samples are also post-annealed in oxygen to improve intergrain connectivity and to optimize the carriers’ density in CuO₂ planes. The results of FIC analysis have shown three-dimensional (3D) and two-dimensional (2D) fluctuations in the order parameters. It has been observed that there is an increase in the cross-over temperature (T _o) as well as in zero resistivity critical temperature {T _c(0)} with Hg-doping. These properties have been further improved after post-annealing in oxygen, which may be due to improved inter-grain coupling and optimization of mobile carriers in CuO₂ planes. A direct correlation between T _o, T _c(0) as well as zero temperature coherence length ξ _c(0) has been observed.     

Magneto-conductivity Analysis for GdBa2Cu3O7−δ Added with Nanosized Ferrite CoFe2O4

Superconducting samples of type (CoFe₂O₄) _x GdBa₂Cu₃O_7?δ , 0.0≤x≤0.1 wt.%, have been prepared by the conventional solid-state reaction technique and characterized using X-ray powder diffraction (XRD) and the scanning electron microscope (SEM). XRD analysis indicates that the orthorhombic structure of Gd-123 is not affected by the nanosized ferrite CoFe₂O₄ addition, whereas the volume fraction of Gd-123 increases with x up to 0.01 wt.%. Nanosized ferrite CoFe₂O₄ has been prepared by Co-precipitation method with grain size about 8 nm. The temperature dependence of electrical resistivity has been measured in zero and 0.44 T magnetic fields. Magneto-conductivity data has been analyzed in terms of Aslamazov–Larkin (AL) and Maki–Thompson (MT) models for layered superconductors, considering the orbital contribution. The superconducting parameters such as the coherence lengths along ab plane ξ _ab (0) and along c-direction ξ _c (0) at 0 K, anisotropic parameter Γ and phase breaking time τ _φ at 100 K have been determined as a function of nanosized ferrite CoFe₂O₄ contents. It is found that the low nanosized CoFe₂O₄ addition contents up to x=0.01 wt.% improves the physical properties of Gd-123, while for x>0.01 wt.% these properties are deteriorated.     

The Study of Purity Improvement on Tl-1223 Thin Films by DC Sputtering and Post-annealing Method

Un-substituted TlBa₂Ca₂Cu₃O _x (Tl-1223)-superconducting thin films have been fabricated on a LaAlO₃ (001) substrate in oxygen by using a two-step method, which includes direct current (DC) magnetron sputtering and post-annealing process. Thallium (Tl) content in amorphous precursor films is found to be important to the crystallization of Tl-superconducting phase. Using the nominal composition of Tl_1+δ Ba₂Ca₂Cu₃ O ₈ (δ = 0.1～0.2) precursor films, the formation is promoted to Tl-1223 and Tl-2223 phase rather than Tl-1212 and Tl-1223 phase with accompanying Tl-rich source pellets. When the annealing process continues, Tl-2223 phase will be converted to Tl-1223 phase at a suitable annealing time and temperature. From the X-ray diffraction pattern, only Tl-1223 (00l) peaks are observed, which shows that the purity of Tl-1223 film is improved significantly by this method. The critical temperature T _c of Tl-1223 film is characterized at 110 K, and the critical current density J _c (77 K, T = 0) is up to 1.5 MA/cm².     

Mechanical and Electrical Properties of (Cu0.5Tl0.5)-1223 Phase Added with Nano-Fe2O3

Superconducting samples of type (Cu_0.5Tl_0.5)-1223 added with nano-Fe₂O₃ (x=0.0, 0.1, 0.2, 0.4, 0.6 and 1.0 wt.%) were prepared by solid-state reaction technique. The prepared samples were characterized using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) for phase analysis and microstructure examination. The elemental content of the prepared samples was determined using particle induced X-ray emission (PIXE), whereas the Oxygen-content of these samples was obtained using non Rutherford backscattering spectroscopy at 3 MeV proton beam. It was found that the Oxygen-content of (Cu_0.5Tl_0.5)-1223 phase was not affected with the addition of nano-Fe₂O₃. The electrical resistivity measurements showed that the superconducting transition temperature (T _c ) increases up to x=0.2 wt.%, followed by a systematic decrease for x>0.2 wt.%. In addition, room temperature Vickers microhardness (H _v ) measurements were carried out at different applied loads (0.49–2.94 N) to study the performance of the mechanical properties of samples. The experimental results of H _v were analyzed using different models such as elastic, energy dissipation, energy balance and modified energy balance models. It has been found that the energy dissipation model is in a good agreement with the microhardness data.     

Effect of Charge Reservoir Layer on the Structural and Transport Properties of CuTlBa<Subscript>2−Y</Subscript>Sr<Subscript><Emphasis Type="Italic">Y</Emphasis></Subscript>-1223 (<Emphasis Type="Italic">Y</Emphasis> = 0 − 0.25) Superconductor

The bulk superconducting composites Cu_0.5Tl_0.5 Ba_2?YSr _Y Ca₂Cu₃O₁0?δ (Y = 0, 0.15, and 0.25) have been synthesized at an ambient pressure. The techniques used to characterize the samples were X-ray scans, Fourier transform infrared spectroscopy (FTIR), and dc resistivity (ρ) measurements. In CuTl-1223 system, we replaced Sr atom at Ba site and studied the superconducting properties of squeezed charge reservoir layer (CRL). From the XRD analysis, it is confirmed that the samples have orthorhombic structure and the dimensional parameters of the unit cell suppressed with the dopant atom which is most probably due to small in size of Sr atom as compared with Ba. The normal-state resistivity and critical temperatures, i.e., T _c (R = 0) and \(T_{\mathrm {c}}^{\text {onset}}\) are observed to be suppressed. The lower values of critical temperature T _c (R = 0) and activation energy U _o (eV) might be possible due to a weak flux pinning. Accordingly, a reduction of weak links and enhanced insulating nature of inter-grain coupling were observed with the doping of Sr atom in CRL. Moreover, the doping in CRL of Sr atom is also confirmed with the FTIR technique. The intrinsic parameters, i.e., coherence length ξ _c(0), crossover temperatures (T _3D?2D), inter-layer coupling (J), etc. were calculated by fluctuation-induced conductivity (FIC) analysis.     

Growth of (Cu0.5Tl0.5?x Hg x )Ba2Ca3Cu4O12?δ Superconductor with Optimal Carrier Density in CuO2 Planes and Fluctuation-Induced Conductivity

The growth of (Cu_0.5Tl_0.5?x Hg _x )Ba₂Ca₃Cu₄O_12??? (x=0, 0.25) superconductor with optimal carrier density in CuO₂ planes has been made possible by partial substitution of Hg at Tl sites in (Cu_0.5Tl_0.5)Ba₂O_4??? charge reservoir layer of (Cu_0.5Tl_0.5)Ba₂Ca₃Cu₄O_12??? superconductor. The fluctuation-induced conductivity (FIC) analysis has been carried out on resistivity vs. temperature curves by using Aslamazov?CLarkin (AL) theory and the results have shown three-dimensional (3D) and two-dimensional (2D) fluctuations in order parameters. The microscopic parameters deduced from FIC analysis such as crossover temperature (T _o ), zero temperature c-axis coherence {?? _c (0)} and the interlayer coupling strength?(J) have been improved with Hg substitution. Also, 3D region has been shifted to higher temperature with Hg substitution. In order to verify the optimal carrier density in CuO₂ planes with Hg substitution, the post-annealing experiments have been carried out on these samples in nitrogen and air. These post-annealing experiments have caused under-doping of carriers from the optimal level resulting into a decrease in T _c (R=0) as well as the magnitude of diamagnetism.     

Optimum Synthesis Temperature of (Cu1?xTlx)Ba2Ca3Cu4O12?δ Superconductor

The effect of synthesis temperature on the superconducting properties of (Cu_1−x Tl _x )Ba₂Ca₃Cu₄O_12−δ (CuTl-1234) samples has been explored. Almost all the superconducting parameters studied in this research work are observed to be suppressed with the increase of synthesis temperature beyond 880 °C, which may be due to impurities caused by the volatility of some constituents such as thallium and oxygen deficiencies as well in the final compound. The Fluctuation Induced Conductivity (FIC) analysis has shown a decrease in the cross-over temperature (T ₀) and the shift of three-dimensional (3D) Aslamasov–Larkin (AL) regions to the lower temperature with the increase of synthesis temperature beyond 880 °C. A direct correlation between the cross-over temperature (T ₀), the zero temperature coherence length {ξ _c (0)}, the zero resistivity critical temperature {T _c (R=0)} as well as carrier concentration has also been observed.     

Effects of cobalt and sintering temperature on electrical properties of Ba0.98Ca0.02Zr0.02Ti0.98O3 lead-free ceramics

Lead-free (Ba_0.98Ca_0.02)(Zr_0.02Ti_0.98)O₃-xmol% (x = 0–1.6) cobalt ceramics (BCZT-xCo) have been fabricated by the traditional solid-state reaction technique and the effects of Co and sintering temperature on ferroelectric, dielectric and piezoelectric properties of (Ba_0.98Ca_0.02)(Zr_0.02Ti_0.98)O₃ lead-free ceramics have been studied systematically. The orthorhombic–tetragonal (T _O–T) transition shift towards lower temperature with increasing Co addition, while Curie temperature (T _c) remained at relatively high value of 107 °C. And the Main piezoelectric parameters are optimized at x = 0.8 mol% with a high piezoelectric coefficient (d ₃₃ = 330 pC/N), a planar mode electromechanical coupling factor (k _p = 46.7 %), a high dielectric constant (ε _r = 2,675) and a low dielectric loss (tanδ = 0.90 %) at 1kHZ. Besides these, high remnant polarization (P _r) and low coercive field (E _c) of 11.5 μC/cm², 0.31 kV/cm are also obtained at (Ba_0.98Ca_0.02)(Zr_0.02Ti_0.98)O₃-0.8 mol%Co lead-free ceramics. Furthermore, greatly enhanced temperature stability of the piezoelectric properties was obtained in the temperature range from 20 to 90 °C. The above results indicate that BCZT-Co ceramics are promising lead-free materials for practical applications.     

Superconductivity of Bi Confined in an Opal Host

Superconductivity is observed in a composite of rhombohedral crystalline bismuth nanoparticles imbedded in an insulating porous opal host via electrical transport and AC magnetic susceptibility. The onset of superconductivity in this system occurs in two steps, with upper transition temperature T _c,U =4.1 K and lower transition temperature of T _c,L =0.7 K, which we attribute to the granular nature of the composite. The transition at T _c,U is observed to split into two transitions with the application of a magnetic field, and these have upper critical fields extrapolated to T=0 K of H _c2,1(0)=0.7 T and H _c2,2(0)=1.0 T, corresponding to coherence lengths of ξ ₁(0)=21 nm and ξ ₂(0)=18 nm, respectively. We suggest that because of the lack of bulk-like states in the Bi nanoparticles due to confinement effects, superconductivity originates from surface states arising from Rashba spin-orbit scattering at the interface.     

Piezoelectric and ferroelectric properties of Ga modified BiFeO3–BaTiO3 lead-free ceramics with high Curie temperature

High-temperature 0.71 Bi(Fe_1?x Ga _x )O₃–0.29 BaTiO₃ (x = 0, 0.01, 0.015, 0.02, and 0.025) piezoelectric ceramics have been synthesized and their structure and electric properties have been investigated systemically. The Ga addition caused insignificant change of crystal structure. However, the addition of a small amount of Ga was quite effective to increase the grain size, densification, and piezoelectric properties. For the ceramics with x = 0.015, the maximum of piezoelectric constant (d ₃₃), and electromechanical coupling factor (k _p) are d ₃₃ = 157 pC/N, k _p = 0.326, respectively. Meanwhile, the increasing Curie temperature (T _c), 467 °C, was obtained with x = 0.02 ceramics. Both remanent polarization P _r and coercive field E _c were reduced with increasing x.     

Fluctuation Induced Conductivity in (Cu0.5Tl0.5)Ba2Ca2Cu3O10?δ Superconductor Synthesized at Different Temperatures

The fluctuation induced conductivity (FIC) analysis of (Cu_0.5Tl_0.5)Ba₂Ca₂Cu₃O_10?δ superconductor synthesized at different temperatures has been carried out in the frame work of Aslamazov-Larkin (AL) theory. Almost all the superconducting parameters studied in this research work have been improved with the increase of synthesis temperature up to 850°C, which is most likely due to (Cu_0.5Tl_0.5)Ba₂Ca₂Cu₃O_10?δ superconducting phase stability at this synthesis temperature. The parameters calculated from FIC analysis are cross-over temperature (T ₀), zero temperature c-axis coherence lengths ξ _c (0), interlayer coupling strength (J) and the exponents (λ _3D and λ _2D). The FIC analysis has shown an increase in T ₀ and the shift of three dimensional (3D) Aslamazov-Larkin (AL) regions to the higher temperature with the increase in synthesis temperature up to 850°C.     

Lead-free (Li, Na, K)(Nb, Sb)O3 piezoelectric ceramics: effect of Bi(Ni0.5Ti0.5)O3 modification and sintering temperature on microstructure and electrical properties

Lead-free (1 ? x)(K_0.475Na_0.475Li_0.05)(Nb_0.95Sb_0.05)O₃–xBi(Ni_0.5Ti_0.5)O₃ [(1 ? x)KNNL–xBNiT] piezoelectric ceramics were prepared by conventional solid-state sintering. The effect of BNiT addition and sintering temperature on phase structure, microstructure, and dielectric and piezoelectric properties of (1 ? x)KNNL–xBNiT ceramics was investigated. The results reveal that the addition of small amounts of BNiT causes significant changes in microstructures, crystalline structures, and dielectric and piezoelectric properties. The T _c values and dielectric constant at T _c of (1 ? x)KNNL–xBNiT ceramics are increased obviously with 0.2 % BNiT addition and decreased with further increasing BNiT content. Enhanced piezoelectric properties are obtained for the sample with x = 0.4 % and synthesized at optimal temperature of 1100 °C, in which d ₃₃ and k _p are 253 pC/N and 0.52, respectively. These results show that (1 ? x)KNNL–xBNiT ceramics are promising lead-free piezoelectric materials.     

Effects of CuO doping on the structure and properties lead-free KNN-LS piezoelectric ceramics

(0.95Na_0.5K_0.5NbO₃-0.05LiSbO₃)-x mol% CuO (KNN-LS-xCuO) lead-free piezoelectric ceramics have been fabricated by a conventional solid-state reaction route at a lower sintering temperature and the effects of CuO-dopant on structure and properties of KNN-LS ceramics have been studied. It is found that the addition of CuO significantly improves the sinterability and properties of KNN-LS ceramics. X-ray diffraction data shows that a small amount of CuO does not change the phase structure of KNN-LS and a dense microstructure with smaller and more uniform grains is developed, probably due to liquid-phase sintering. With the increase of CuO content x, the relative density, d ₃₃ , k _p , tanδ and Q _m have been improved obviously when x < 0.45 due to the presence of the liquid phase and the refined grains, but excessive CuO would degrade the comprehensive properties of KNN-LS-xCuO ceramics. The best specimen with a high relative density of 98.53 % was fabricated when x = 0.45 at 1,060 °C, relating constants respectively are: d ₃₃  = 175pC/N, k _p  = 0.46, ε _r  = 551.23, tanδ = 1.41 %, Q _m  = 41.5.     

Isovalent Substitution and Heat Treatments Control of T c, Chain Oxygen Disorder and Structural Phase Transition in High T c Superconductors (Y1−x Nd x )SrBaCu3O6+z

We report here on the preparation, X-ray diffraction with Rietveld refinement, AC magnetic susceptibility measurements and effect of heat treatments in (Y_1?x Nd _x )SrBaCu₃O_6+z . Each sample was subject to two types of heat treatment: oxygen annealing [O] and argon annealing followed by oxygen annealing [AO]. For each x, the [AO] heat treatment increases the orthorhombicity ε=(b?a)/(b+a) (for 0≤x<1), T _c (for x>0.2) and the distance d[Cu(1)–(Sr/Ba)] (decrease T _c) for x<0.25 and decrease it (increase T _c) for x>0.25. When x increase from 0 to 1, ε decreases to 0 with transition from orthorhombic to tetragonal structure. ε[O] decreases with T _c[O]. However, T _c[AO] decreases with ε[AO] until x=0.2, increases for x=0.4 and after it decreases by 9.8 K to 77.2 K for x=1 [AO]. Remarkable correlations were observed between T _c(x) and the volume of the unit cell V(x); and between δT _c(x)=T _c[AO]?T _c[O] and δε(x). A combination of several factors such as decrease in d[Cu(1)–(Sr/Ba)]; increase in cationic and chain oxygen ordering; the number p _sh(x) of holes by Cu(2)–O₂ superconducting plans and in-phase purity for the [AO] samples may account for the observed data.