• Dinesh

      Articles written in Bulletin of Materials Science

    • Composition dependence of transition temperature in new superconductors: La2 −x(Ba, Sr)xCuO4

      R K Singh A C Sharma N K Gaur Dinesh Varshney

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      We have investigated the variation of transition-temperature and coupling parameter with the composition concentration in La2 −x(Ba, Sr)xCuO4 superconductors using a formulation developed on the basis of an idea of pairing of charge carriers by exchange of both acoustic plasmons and phonons. Reasonably good agreement is found between the recent experimental results and our theoretical results on the superconducting transition temperature.

    • Composition dependence of transition temperature in some ceramic superconductors

      R K Singh Dinesh Varshney N K Gaur A C Sharma

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      The composition dependence of transition temperature in some ceramic superconductors (La2−x(Ba, Sr)xCuO4) was studied by modifying our earlier approach and developing a Fourier-transformed effective potential which involves the effect of two-dimensional (2D) acoustic plasmons. This potential was used to obtain the pairing (electron-electron attraction) parameter (λ), the averaged Coulomb repulsive parameter (μ*) and the cut-off 2D acoustic plasmon frequency (ωc) required to compute the superconducting transition temperature (Tc) from the strong coupling theory. The variations ofTc with compositions (x) obtained for La2−x(Ba, Sr)xCuO4 show reasonably good agreement with experimental data.

    • Study of doping effects on transition temperature of La2 −x (Ca, Na, K)xCuO4 superconductors

      R K Singh Dinesh Varshney N K Gaur

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      We have investigated doping effects on the transition temperature (Tc) of La2 −xMxCuO4 (M=Ca, Na and K) by incorporating the effects of two-dimensional (2D) acoustic plasmons in the framework of the strong coupling theory. The contributions from 2D acoustic plasmon mechanism toTc have been obtained from a Fourier-transformed effective potential, which has been earlier found to be successful in predicting the composition dependence ofTc in La2 −x(Ba, Sr)xCuO4. The results obtained by us on the variation of transition temperature with composition (x) in La2−xMxCuO4 superconductors are in reasonably good agreement with the available experimental data. This success has led to the conclusion that 2D acoustic plasmons are adequate to explain the pairing mechanism and the variation ofTc with composition (x) in cuprate superconductors.

    • Effect of doping concentration on normal state resistivity of La2 −x (Ba, Sr)x CuO4 superconductors

      Dinesh Varshney R K Singh

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      Based on free electron layered electron gas model of quasi two dimensional CuO2 layers in La(Ba/Sr)CuO superconductors a model potentialV(q) is developed earlier with the electron-electron and electron-phonon interactions. The model approach facilitates the dielectric functions and the dispersion relations of 2D acoustic phonon and plasmon modes. We have then worked out the coupling strength (γ) linking electrons to the 2D acoustic phonon mode (ħω_) from the residue at the pole ofV(q). Furthermore, the scattering time (τe−ph) during electron-phonon interaction (EPI) for this simplified system is also estimated. The contribution to the normal state in plane resistivity due to EPI is then evaluated. Finally, the variations ofτ andρ is studied with the doping concentration (x) and temperature (T) and the results obtained by us show reasonably good agreement with the available experimental data.

    • Effect of oxygen deficiency (δ) on transition temperature of yttrium cuprate superconductors

      R K Singh Dinesh Varshney A K Khaskalam

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      The nature of pairing mechanism as well as transition temperature of yttrium cuprates is discussed using the strong coupling theory. An interaction potential has been developed for the layered structure with two conducting CuO2(a–b) layers in a unit cell. The interaction potential properly takes care of electron-electron, electron-phonon and electron-plasmon interactions. Furthermore, the electron-phonon coupling parameter (λ), the modified Coulomb repulsive parameter (μ*) and the 2D acoustic phonon (plasmon) energy as a function of oxygen deficiency is worked out. Finally, the superconducting transition temperature (Tc) is then evaluated by using these coupling parameters and obtainedTc = 95(92)K for Y(Yb)Ba2Cu3O7−δ superconductors withδ = 0·0. The model parameters estimated from the layered structure approach are consistent with the strong coupling theory. The result deduced on the variation ofTc withδ are in fair agreement with the earlier reported data on yttrium cuprates. The analysis of the above results are discussed.

    • Oxygen deficiency dependence of transition temperature in (Sm, Er) Ba2Cu3O7−δ superconductors

      R K Singh Dinesh Varshney Amit K Khaskalam

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      We have investigated the effects of oxygen deficiency (δ) on the transition temperature (Tc) of (Sm, Er)Ba2Cu3O7−δ superconductors by incorporating the effects of the two dimensional (2D) acoustic phonons and plasmons in the framework of strong coupling theory. The proposed approach for yttrium cuprates properly takes care of the double CuO2 plane in a unit cell and has been found earlier to be successful in describing the pairing mechanism as well as the variation ofTc withδ in Y Ba2Cu3O7−δ system. The coupling strength (λ), the screening parameter (μ*) and the two dimensional acoustic phonon (plasmon) energyħω+) as a function of oxygen deficiency is worked out. Finally, the transition temperature is evaluated and is found to be consistent with the earlier experimental data on yttrium cuprates. Thus, coupled phonon-plasmon mechanism is adequate to understand the nature of pairing mechanism and oxygen deficiency dependence of transition temperature in 90 K (Sm, Er)Ba2Cu3O7−δ superconductors.

    • Two-component model for optical conductivity in Y-Ba-CuO superconductors

      Dinesh Varshney Sanjay Shah R K Singh

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      The optical conductivity of optimized doped YBa2Cu3O7-δ (δ=0·0,Tc=92 K) superconductors, which are frequency dependent, has been theoretically investigated based on two-component (Drude and mid infrared terms) approach within the Fermi liquid description. Our approach incorporates the Drude contribution as well as hopping of charge carriers in the model dielectric function along with the structure factor. It explains the anomalies observed in the optical measurements for the normal state as the frequency dependence of optical conductivity using the Drude term which gives a sharp peak at zero frequency, and a long tail at higher frequencies, i.e. in the infrared region. The extra term (hopping carriers) gives a peak value in the optical conductivity centred in the mid infrared region. The two species of charge carriers contribution to the conduction in the CuO chain layer as well as CuO2 layer will account for the optical conductivity in the mid infrared as well as infrared frequency regions. The analysis reveals an interesting relation$$\sigma _{CuO_2 layer} \approx 3\sigma _{chain layer} $$, and the nature for optical conduction with energy is similar qualitatively, the only difference is quantitatively. It is shown that the analysis is consistent with the published data on optical conductivity in optimized-doped YBa2Cu3O7-δ superconductors.

    • Effect of oxygen deficiency (δ) on normal state resistivity of YBa2Cu3O7-δ superconductors

      Dinesh Varshney R K Singh Amit K Khaskalam

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      We have investigated theoretically the effect of oxygen deficiency (δ) on normal state resistivity (ρ) as well as its temperature dependence in YBa2Cu3O7-δ superconductors. This has been based on a potential which incorporates the structure factors and various interactions for double two-dimensional (2-D) conducting CuO2 plane. Using the Coulomb and electron-phonon terms of the interaction potential, we have then worked out the coupling strength (γ) for neighbouring electrons linked via 2-D acoustic phonons (_). Furthermore, the scattering time (τe-ph) due to electron-phonon interaction is deduced. The variations inτe-ph andρe-ph are studied with oxygen deficiency (δ) which is in the range of 0·0≤δ≤1·0, and the results thus obtained are found to be consistent with the earlier reported data. The residual resistivityρ0 obtained by extrapolation from experimental data together withρe-ph will predict the nearly-linear behaviour of normal state resistivity at temperatures (T) [90≤T≤300 K] in YBa2Cu3O7-δ superconductors.

    • Specific heat studies in Ho-Ba-CuO superconductors: Fermionic and bosonic contributions

      Dinesh Varshney Sanjay Shah R K Singh

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      The specific heats of superconducting HoBa2Cu3O7-δ (Tc≅ 92 K) have been theoretically investigated in the temperature domain 70 ≤T ≤110 K. The bosonic (phonons) contribution to the specific heat is estimated from Debye model in the harmonic approximation for high temperature expansion (T > θD/2π) using the moments of the phonon density of states. The fermionic constituent as the electronic specific heat is deduced using a suitable trial function above and belowTc. As a next step the contribution of specific heat by charge oscillations (plasmons) are obtained. The theoretical results from bosonic and fermionic terms are then compared with the experimental results. We find that the specific heats from electronic as well as plasmon term are only a fraction of lattice specific heat and in particular, plasmons do not influence the thermal conduction significantly. The implications of the above analysis are discussed.

    • Semiconductor applications of plasma immersion ion implantation technology

      Mukesh Kumar Rajkumar Dinesh Kumar P J George

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      Many semiconductor integrated circuit manufacturing processes require high dose of implantation at very low energies. Conventional beam line ion implantation system suffers from low beam current at low energies, therefore, cannot be used economically for high dose applications. Plasma immersion ion implantation (PIII) is emerging as a potential technique for such implantations. This method offers high dose rate irrespective of implantation energy. In the present study nitrogen ions were implanted using PIII in order to modify the properties of silicon and some refractory metal films. Oxidation behaviour of silicon was observed for different implantation doses. Diffusion barrier properties of refractory barrier metals were studied for copper metallization.

    • X-ray structure determination and analysis of hydrogen interactions in 3,3′-dimethoxybiphenyl

      Rajnikant Dinesh Dalbir Singh

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      The crystal structure of 3,3′-dimethoxybiphenyl has been determined by X-ray diffraction methods with an aim of describing the hydrogen interaction in biphenyl derivatives. The title compound crystallizes in monoclinic space group 𝑃21/𝑐 with unit cell dimensions, 𝑎 = 7.706(1), 𝑏 = 11.745(2), 𝑐 = 12.721(2) Å, 𝛽 = 92.31(1)°, 𝑍 = 4 and its structure has been refined up to the reliability index of 3.8%. The average torsion angle about the inter-ring C–C bond is 37.5°. The O1 and O1′ atoms of the methoxy group are deviated by 0.046(1) Å and 0.234(1) Å from the mean planes of respective rings. The crystal cohesion is pronounced due to three-inter-molecular C–H…O hydrogen bonds.

    • X-ray analysis of 2-aniline benzo(2,3-𝑏) cyclopentane-1,3-dione

      Rajnikant Dinesh Mousmi M B Deshmukh Anshu Sawhney

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      The molecular and crystal structure of 2-aniline benzo(2,3-𝑏) cyclopentane-1,3-dione has been determined by X-ray crystallographic techniques. This compound crystallizes in the orthorhombic space group 𝑃212121 with unit cell parameters: 𝑎 = 5.467(1), 𝑏 = 10.657(3), 𝑐 = 19.602(6) Å; 𝑉 = 1142.01(5) Å3, 𝑍 = 4. The crystal structure has been resolved up to an 𝑅-factor 0.050 for 1129 reflections. All the three rings in the structure are planar. However, the dihedral angle between the phenyl ring and the moiety comprising of a five-membered and six-membered ring is 92.4°. The oxygen atom O1 acts as a trifurcated acceptor and is involved in the formation of three intermolecular interactions.

    • Superconductivity and electrical resistivity in alkali metal doped fullerides: Phonon mechanism

      Dinesh Varshney A Dube K K Choudhary R K Singh

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      We consider a two-peak model for the phonon density of states to investigate the nature of electron pairing mechanism for superconducting state in fullerides. We first study the intercage interactions between the adjacent C60 cages and expansion of lattice due to the intercalation of alkali atoms based on the spring model to estimate phonon frequencies from the dynamical matrix for the intermolecular alkali-C60 phonons. Electronic parameter as repulsive parameter and the attractive coupling strength are obtained within the random phase approximation. Transition temperature, 𝑇c, is obtained in a situation when the free electrons in lowest molecular orbital are coupled with alkali-C60 phonons as 5 K, which is much lower as compared to reported 𝑇c (≈ 20 K). The superconducting pairing is mainly driven by the high frequency intramolecular phonons and their effects enhance it to 22 K. To illustrate the usefulness of the above approach, the carbon isotope exponent and the pressure effect are also estimated. Temperature dependence of electrical resistivity is then analysed within the same model phonon spectrum. It is inferred from the two-peak model for phonon density of states that high frequency intramolecular phonon modes play a major role in pairing mechanism with possibly some contribution from alkali-C60 phonon to describe most of the superconducting and normal state properties of doped fullerides.

    • Weak C–H…O hydrogen bonds in alkaloids: An overview

      Rajnikant Dinesh Kamni

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      An overview of general classification scheme, medicinal importance and crystal structure analysis with emphasis on the role of hydrogen bonding in some alkaloids is presented in this paper. The article is based on a general kind of survey while crystallographic analysis and role of hydrogen bonding are limited to only those alkaloids whose three-dimensional structure has been reported by us. The C–H…O hydrogen bonding in the solid state in alkaloids has been found to be predominant and this observation makes the role of hydrogen bonding in organic molecular assemblies very important.

    • Pressure dependence of elastic properties of ZnX (X = Se, S and Te): Role of charge transfer

      Dinesh Varshney P Sharma N Kaurav R K Singh

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      An effective interaction potential (EIOP) is developed to invoke the pressure induced phase transition from zinc blende (𝐵3) to rocksalt (𝐵1) structure and anharmonic properties in ZnX (X = Se, S, Te) semiconductors. The effective interaction potential incorporates the long range Coulomb interaction, van der Waals interaction and short-range repulsive interaction up to second neighbour ions within the Hafemeister and Flygare approach as well as the charge transfer effects caused by the electron-shell deformation of the overlapping ions. The van der Waals coefficients are computed by the Slater Kirkwood variation method as a first step. Later on, we evaluate volume collapse, second order and third order elastic constants with pressure pointing to the systematic trends in all compounds of zinc blende structure and their thermal properties such as force constant, Gruneisen parameter, compressibility, Debye temperature etc. The vast volume discontinuity in pressure–volume (PV) phase diagram identifies the structural phase transition from zinc blende (𝐵3) to rock salt (𝐵1) structure and is consistent with those revealed from earlier reports.

    • Synthesis, X-ray structure and N–H…O interactions in 1,3-diphenyl-urea

      Rajnikant Dinesh M B Deshmukh Kamni

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      The synthesis, X-ray structure and role of intermolecular interactions have been studied in case of 1,3-diphenyl-urea, owing to its medicinal importance. The compound crystallizes in orthorhombic crystal system (space group, 𝑃𝑛𝑎21) with unit cell parameters, 𝑎 = 9.118(3), 𝑏 = 10.558(2), 𝑐 = 11.780(3) Å and 𝑍 = 4. The structure has been solved by direct methods and refined to a final 𝑅-value of 0.0316. The oxygen atom of the carbonyl group is responsible for the existence of two N–H…O intermolecular interactions.

    • Photocatalytic degradation of rhodamine B dye using hydrothermally synthesized ZnO

      K Byrappa A K Subramani S Ananda K M Lokanatha Rai R Dinesh M Yoshimura

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      The sunlight mediated photocatalytic degradation of rhodamine B (RB) dye was studied using hydrothermally prepared ZnO (𝑇 = 150°C and 𝑃 ∼ 20–30 bars). Zinc chloride was used as the starting material along with sodium hydroxide as a solvent in the hydrothermal synthesis of ZnO. Different durations were tried to obtain pure ZnO phase, which was later confirmed through powder X-ray diffraction. The photocatalytic behaviour of the prepared ZnO was tested through the degradation of RB. The disappearance of organic molecules follows first-order kinetics. The effect of various parameters such as initial dye concentration, catalyst loading, pH of the medium, temperature of the dye solution, on the photo degradation of RB were investigated. The thermodynamic parameters of the photodegradation of RB, like energy of activation, enthalpy of activation, entropy of activation and free energy of activation revealed the efficiency of the process. An actual textile effluent containing RB as a major constituent along with other dyes and dyeing auxiliaries was treated using hydrothermally synthesized ZnO and the reduction in the chemical oxygen demand (COD) of the treated effluent revealed a complete destruction of the organic molecules along with colour removal.

    • Effect of thin Mo2C layer on thermal stability of Si/SiO2/Ti/Cu system

      C C Tripathi Mukesh Kumar Dinesh Kumar

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      The effect of introducing a thin Mo2C (30 nm) layer between Ti and Cu on the thermal stability of Si/SiO2/Ti/Cu system was studied using four-point probe (FPP), scanning electron microscopy (SEM), energydispersive X-ray spectroscopy (EDAX) and X-ray diffraction (XRD) techniques. The measured value of the sheet resistance in the bi-layered diffusion barrier structure does not show any change up to an annealing temperature of 750°C. The sheet resistance when measured after annealing at 800°C marginally increases but less than twice its value at room temperature. The XRD analysis indicated no copper diffusion and the formation of Cu3Si phase up to 800°C. The bi-layered barrier structure annealed at elevated temperature shows copper-depleted and agglomerated regions. The sheet resistance measurement, study of surface morphology and the XRD analysis confirm that the insertion of thin Mo2C layer increases the thermal stability of the system from 400°C to 750°C. The increased thermal stability of the system is ascribed to longer diffusion path length in the bi-layered system probably because of grain boundaries mismatch at Ti–Mo2C interface.

    • Bromine pretreated chitosan for adsorption of lead (II) from water

      Rajendra Dongre Minakshi Thakur Dinesh Ghugal Jostna Meshram

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      Pollution by heavy metals like lead (II) is responsible for health hazards and environmental degradation. Adsorption is a prevalent method applied for removal of heavy metal pollutants from water. This study explored adsorption performances of 30% bromine pretreated chitosan for lead (II) abatement from water. Bromine pretreatment alters porosity and specific surface area of chitosan by means of physicochemical interaction with cationic sites of chitosan skeleton, besides imparting anionic alteration at amino linkages of chitosan, to remove lead (II) by chemical interactions on superfluous active sites as characterized by FTIR, SEM, DTA and elemental analysis. Lead adsorptions were studied in batch mode by varying parameters viz. pH, bromine loading, sorbent dosage, initial lead concentration, contact time and temperature. The adsorption equilibrium data was well fitted to Freundlich isotherm and maximum sorption capacity of 30% bromine pretreated chitosan sorbent was 1.755 g/kg with 85–90% lead removal efficiency. Though cost and applicability of sorbent is unproven, yet contrast to raw chitosan derivatives, activated carbons and some resins, 30% bromine pretreated chitosan endow benign and efficient lead abatement technique.

    • Synthesis and characterization of nickel/barium hexa-aluminate composite coatings

      Dinesh Kumar Sampada Gurav Vikram Jayaram Sanjay Kumar Biswas

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      Electrodeposition of nickel/barium hexa-aluminate (Ni/BHA) composite coatings has been carried out from a Watt’s bath on mild steel substrate. BHA powders with plate habit were synthesized by solution combustion synthesis followed by heat treatment to ensure complete conversion to the hexa-aluminate phase. Heat treated material was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) combined with X-ray analysis. The dispersion behaviour and stability of BHA suspensions with cationic and anionic surfactants at room temperature were studied by dynamic light scattering under different pH. The influence of BHA concentration in the electrolytic bath, deposition temperature, pH, current density and duty cycle on particle incorporation in the coatings were studied and conditions for maximum particle incorporation were established. Coatings with a roughness of about 0.4 𝜇m were produced by using this technique. Effect of BHA content on microhardness was also investigated. A reasonably good thickness of the coatings was achieved in a given set of conditions.

    • An investigation on microwave sintering of Fe, Fe–Cu and Fe–Cu–C alloys

      Raja Annamalai Anish Upadhyaya Dinesh Agrawal

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      The powder characteristics of metallic powders play a key role during sintering. Densification and mechanical properties were also influenced by it. The current study examines the effect of heating mode on densification, microstructure, phase compositions and properties of Fe, Fe–2Cu and Fe–2Cu–0.8C systems. The compacts were heated in 2.45 GHz microwave sintering furnaces under forming gas (95%N2–5%H2) at 1120 °C for 60 min. Results of densification, mechanical properties and microstructural development of the microwave-sintered samples were reported and critically analysed in terms of various powder processing steps.

    • Effect of anodization on corrosion behaviour and biocompatibility of Cp-titanium in simulated body fluid

      Archana Singh B P Singh Mohan R Wani Dinesh Kumar J K Singh Vakil Singh

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      The objective of this investigation is to study the effectiveness of anodized surface of commercial purity titanium (Cp-Ti) on its corrosion behaviour in simulated body fluid (SBF) and proliferation of osteoblast cells on it, to assess its potentiality as a process of surface modification in enhancing corrosion resistance and osseointegration of dental implants. Highly ordered nano-porous oxide layer, with nano-sized pores, is developed on the surface of Cp-Ti through electrochemical anodization in the electrolyte of aqueous solution of 0.5% HF at 15 V for 30 min at 24 °C. The nano-porous feature of the anodized surface is characterized by field-emission scanning electron microscope (FESEM). Pores of some anodized samples are sealed by exposing the anodized surface in boiling water. Corrosion behaviour of the anodized specimen is studied in Ringer’s solution at 30 ± 2 °C, using electrochemical impedance and cyclic polarization technique. Biocompatibility of the anodized surface is accessed using MG63 osteoblast cells. Both corrosion as well as pitting resistance of Cp-Ti in simulated body fluid are found to be highest in the anodized and sealed condition and followed in decreasing order by those of anodized and unanodized ones. Significantly higher MG63 osteoblast cell proliferations are found on the anodized surface than that on the unanodized one. Anodized Cp-Ti develops nano-size surface pores, like that of natural bone. It enhances corrosion and pitting resistance and also the process of osteoblast cell proliferation on Cp-Ti.

    • Phonon, magnon and electron contributions to low temperature specific heat in metallic state of La0.85Sr0.15MnO3 and Er0.8Y0.2MnO3 manganites

      Dinesh Varshney Irfan Mansuri E Khan

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      The reported specific heat 𝐶\ (𝑇) data of the perovskite manganites, La0.85Sr0.15MnO3 and Er0.8Y0.2MnO3, is theoretically investigated in the temperature domain 3 ≤ 𝑇 ≤ 50 K. Calculations of 𝐶\ (𝑇) have been made within the three-component scheme: one is the fermion and the others are boson (phonon and magnon) contributions.Lattice specific heat is well estimated fromthe Debye temperature for La0.85Sr0.15MnO3 and Er0.8Y0.2MnO3 manganites. Fermion component as the electronic specific heat coefficient is deduced using the band structure calculations. Later on, following double-exchange mechanism the role of magnon is assessed towards specific heat and found that at much low temperature, specific heat shows almost T3/2 dependence on the temperature. The present investigation allows us to believe that electron correlations are essential to enhance the density of states over simple Fermi-liquid approximation in the metallic phase of both the manganite systems. The present numerical analysis of specific heat shows similar results as those revealed from experiments.

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