Bloch-Gruneisen Model Research Articles

One Structure, Two Elements-LuGe2 Superconductor vs Ordinary Metallic Conductor LuSn2. A Case Study on How Site-Selective Germanium for Tin Atom Substitution Leads to Modulating of the Charge Distribution.

The substitution of chemically similar elements in a given crystal structure is an effective way to enhance physical properties, but the understanding on such improvements is usually impeded because the substitutions are random, and the roles of the different atoms cannot be distinguished by crystallographic symmetry. Herein, we provide a detailed crystallographic analysis and property measurements for the continuous solid solutions LuGexSn2-x (0 < x < 2). The results show that there is no apparent change of the global symmetry, with the end-members LuGe2 and LuSn2, as well as the intermediate LuGexSn2-x compositions adopting the ZrSi2 type structure (space group Cmcm, Pearson index oC12). Yet, the refinements of the crystal structures from single-crystal X-ray diffraction data show that Ge-Sn atom substitutions are not random, but occur preferentially at the zigzag chain. The patterned distribution of two group 14 elements leads to a significant variation in chemical bonding and charge ordering within the other structural fragment, the 2D square nets, thereby resulting in tuned electron transport. The enhancement is greater than that for the typical Bloch-Gruneisen model and more akin to that for the parallel-resistor model. Magnetization measurements on single crystals show bulk superconductivity in all LuGexSn2-x samples with shielding fractions as high as 90%. Specific heat data confirm the effect to originate from residual metallic tin in the material, indicating that Sn atom substitutions in the 2D square nets cause disruptions of the hypervalent bonding and local anisotropy, which ultimately leads to vanishing of the superconducting state in the end-member LuGe2. This work sheds light on how the complexity in chemical interactions by two different carbon congeners leads to changes in the physical properties and how they can be correlated with the induced charge distribution. These studies also provide a general approach to modulation of charge density and. thus, of emerging physical properties in other classes of intermetallic systems based on the main-group elements of groups 13 to 15.

Antiferromagnetism in EuNiGe3

The synthesis and crystallographic and physical properties of polycrystalline EuNiGe3 are reported. EuNiGe3 crystallizes in the noncentrosymmetric body-centered tetragonal BaNiSn3-type structure. The physical property data consistently demonstrate that this is a metallic system in which Eu spins S = 7/2 order antiferromagnetically at a temperature TN = 13.6 K. Magnetic susceptibility chi data for T > TN indicate that the Eu atoms have spin 7/2 with g = 2, that the Ni atoms are nonmagnetic, and that the dominant interactions between the Eu spins are ferromagnetic. Thus we propose that EuNiGe3 has a collinear A-type antiferromagnetic structure. A fit of chi(T < TN) by our molecular field theory is consistent with a collinear magnetic structure. Electrical resistivity rho data from TN to 350 K are fitted by the Bloch-Gruneisen model for electron-phonon scattering, yielding a Debye temperature of 265(2) K. A strong decrease in rho occurs below TN due to loss of spin-disorder scattering. Heat capacity data at 25 K < T < 300 K are fitted by the Debye model, yielding the same Debye temperature 268(2) K as found from rho(T). The extracted magnetic heat capacity is consistent with S = 7/2. The magnetic entropy at TN = 13.6 K is 83% of the expected asymptotic high-T value, with the remainder recovered by 30 K.

Structural, thermal, magnetic, and electronic transport properties of the LaNi2(Ge1−xPx)2system

Polycrystalline samples of LaNi2(Ge{1-x}P{x})2 (x = 0, 0.25, 0.50, 0.75, 1) were synthesized and their properties investigated by x-ray diffraction (XRD), heat capacity Cp, magnetic susceptibility chi, and electrical resistivity rho measurements versus temperature T. These compounds all crystallize in the body-centered-tetragonal ThCr2Si2-type structure. The rho(T) measurements indicate that all compositions in this system are metallic. The low-T Cp measurements yield a rather large Sommerfeld coefficient gamma = 12.4(2) mJ/mol K^2 for x = 0 reflecting a large density of states at the Fermi energy that is comparable with the largest values found for the AFe2As2 class of materials with the same crystal structure. The gamma decreases approximately linearly with x to 7.4(1) mJ/mol K^2 for x = 1. The chi measurements show nearly temperature-independent paramagnetic behavior across the entire range of compositions except for LaNi2Ge2, where a broad peak is observed at 300 K from chi(T) measurements up to 1000 K that may arise from short-range antiferromagnetic correlations in a quasi-two-dimensional magnetic system. High-accuracy Pade approximants representing the Debye lattice heat capacity and Bloch-Gruneisen electron-phonon resistivity functions versus T are presented and are used to analyze our experimental Cp(T) and rho(T) data, respectively. The T-dependences of rho for all samples are well-described by the Bloch-Gruneisen model, although the observed rho(300 K) values are larger than calculated from this model. A significant T-dependence of the Debye temperature determined from the Cp(T) data was observed for each composition. No clear evidence for bulk superconductivity or any other long-range phase transition was found for any of the compositions studied.

Interpretation of metallic and semiconducting temperature dependent resistivity of La 0.91Rb 0.06Mn 0.94O 3 manganites

The present paper focuses on a quantitative analysis of the metallic and semiconducting behavior of electrical resistivity in La 0.91Rb 0.06Mn 0.94O 3 manganites. The contribution of inherent low-frequency acoustic phonons as well as high-frequency optical phonons, to the electron–phonon resistivity is estimated following Bloch–Gruneisen model. The computed phonon resistivity is compared with that of reported metallic resistivity, accordingly ρ diff. = [ ρ exp. − { ρ 0 + ρ e-ph (= ρ ac + ρ op)}] have been analysed through electron-electron scattering. Also, the difference can be varies linearly with T 4.5 in accordance with the electron–magnon scattering in the double exchange process. The results reveal important aspects transport mechanism as well as point out that it is not only dominated by electron–phonon scattering, but also by electron–electron and electron–magnon scattering process. Alternatively, in high temperature regime ( T > T P ) the semiconducting nature is discussed with Mott’s variable range hopping (VRH) and small polaron conduction (SPC) model.

Interpretation of temperature dependence of the in-plane electrical resistivity in YBa 2Cu 4O 8: Electron–phonon approach

In this paper, we undertake a quantitative analysis of observed temperature-dependent in-plane normal state electrical resistivity of single crystal YBa 2Cu 4O 8. The analysis is within the framework of classical electron–phonon i.e., Bloch-Gruneisen model of resistivity. It is based on the inherent acoustic (low frequency) phonons ( ω ac ) as well as high frequency optical phonons ( ω op ), the contributions to the phonon resistivity were first estimated. The optical phonons of the oxygen breathing mode yields a relatively larger contribution to the resistivity compared to the contribution of acoustic phonons. Estimated contribution to in-plane electrical resistivity by considering both phonons i.e., ω ac and ω op , along with the zero-limited resistivity, when subtracted from single crystal data infers a quadratic temperature dependence over most of the temperature range [80 ⩽ T ⩽ 300]. Quadratic temperature dependence of ρ diff. = [ ρ exp − { ρ 0 + ρ e − ph (= ρ ac + ρ op )}] is understood in terms of electron–electron inelastic scattering. The relevant energy gap expressions within the Nambu-Eliashberg approach are solved imposing experimental constraints on their solution (critical temperature T c ). It is found that the indirect-exchange formalism provides a unique set of electronic parameters [electron–phonon ( λ ph ), electron-charge fluctuations ( λ pl ), electron–electron ( μ) and Coulomb screening parameter ( μ *)] which, in particular, reproduce the reported value of T c .

Explanation of non-linear in-plane electrical resistivity of YBa2Cu4O8: electron-phonon approach

The temperature-dependent in-plane normal state electrical resistivity of single crystal YBa2Cu4O8is theoretically analysed within the framework of classical electron-phonon i.e., Bloch-Gruneisen model of resistivity. The contributions to the resistivity due to the inherent acoustic phonons as well as high frequency optical phonons were first estimated. Estimated contribution to in-plane electrical resistivity by considering both phonons along with the zero limited resistivity, when subtracted from single crystal data infers a quadratic temperature dependence over most of the temperature range which is understood in terms of electron-electron inelastic scattering. The value of the electron-phonon coupling strength and of the Coulomb screening parameter obtained from the static dielectric function with the two-dimensional model and is in the strong coupling limit. As an application of the proposed model, the superconducting transition temperature Tc is also estimated. Apart from phonons if we add charge density waves for pairing, we retrieve the experimental reported Tc value.

Effect of electron/hole doping on the transport properties of lanthanum manganitesLaMnO3

We report the results of electrical resistivity, magnetic susceptibility andthermoelectric power measurements on the stoichiometric hole-dopedLa0.8Ca0.2MnO3 andelectron-doped La0.8Ce0.2MnO3 manganites. The resistivity and thermopower data show a metal–insulator phase transitionfor both samples. Magnetic susceptibility measurement confirms that both the samplesundergo a transition from paramagnetic to ferromagnetic phase at defined Curie temperaturesTc = 240 K(La0.8Ca0.2MnO3) and263 K (La0.8Ce0.2MnO3). The electrical resistivity data are then theoretically analysed within the framework of theclassical electron–phonon model of resistivity, i.e. the Bloch–Gruneisen model. Detailed analysisof the electrical resistivity of electron- and hole-doped manganites suggests that besides theelectron–phonon effect another possibility for the change in carrier density arises due to thepresence of electron correlation in the metallic system. From the thermopowerS(T) results, we suggest that its behaviour is determined by competition among the severaloperating scattering mechanisms for the heat carriers and a balance between carrierdiffusion and phonon drag contributions in the polycrystalline samples of hole-dopedLa0.8Ca0.2MnO3 andelectron-doped La0.8Ce0.2MnO3 manganites.

Interpretation of Temperature-Dependent Resistivity of La–Pb–MnO3: Role of Electron–Phonon Interaction

The present paper deals with the theoretical investigation of temperature-dependent resistivity of the perovskite manganites La0.78Pb0.22MnO3-δ within the framework of the classical electron–phonon model of resistivity, i.e., the Bloch–Gruneisen model. Due to inherent acoustic (low-frequency) phonons (ωac) as well as high-frequency optical phonons (ωop), the contributions to the electron–phonon resistivity have first been estimated. At low temperatures the acoustic phonons of the oxygen-breathing mode yield a relatively larger contribution to the resistivity as compared to the contribution of optical phonons. Furthermore, the nature of phonons changes around T = 215 K exhibiting a crossover from an acoustic to optical phonon regime with elevated temperature. The contribution to resistivity estimated by considering both phonons, i.e., ωac and ωop, when subtracted from experimental data, infers a T4.5 temperature dependence over most of the temperature range. Deduced T4.5 temperature dependence of ρdiff = [ρexp − {ρ0 + ρe-ph( = ρac + ρop)}] is justified in terms of electron–magnon scattering within the double exchange (DE) process. Within the proposed scheme, the present numerical analysis of temperature dependent resistivity shows similar results as those revealed by experiments

Interpretation of the temperature-dependent resistivity ofK3C60 fulleride superconductors: an electron–phonon mechanism

The temperature-dependent normal state resistivity of single crystalK3C60 is theoretically analysed within the framework of the electron–phonon model ofresistivity, i.e., the Bloch–Gruneisen model. Keeping in mind that a largeamount of impurities develop due to the doping of alkali metal in pureC60, zerotemperature limited resistivity has first been estimated. Due to the inherent intermolecular phonon(ωer) andintramolecular (ωra) phonon, the contributions to the resistivity have been estimated as a next step. Theintramolecular phonon yields a relatively larger contribution to the resistivitycompared to the contribution of intermolecular phonons above 260 K. In addition,below this temperature, the intermolecular phonon is a major source of resistivity.The estimated contribution to resistivity when subtracted from single crystaldata infers a quadratic temperature dependence till 200 K and there exists adeparture until near room temperature. The power temperature dependence ofρdiff = [ρexp−{ρ0+ρe−ph (= ρer+ρra)}] may be attributed to the contribution of the three dimensional transport mechanismand has been related to electron–electron interaction. We then emphasizedthe role of intramolecular phonons to estimate the transition temperatureTc, carbon isotopeeffect exponent α and pressure as well as the volume derivative ofTc and the results are consistent with the reported data. It therefore appears that bothelectron–electron and electron–phonon interaction play an important role in retracing thenormal state resistivity behaviour and some of the superconducting state properties.

Electrical resistivity in the ferromagnetic metallic state of La-Ca-MnO$\mathsf{_{3}}$: Role of electron-phonon interaction

The temperature-dependent resistivity of the perovskite manganites La1-x Ca x MnO3, with x = 0.33, is theoretically analysed within the framework of the classical electron-phonon model of resistivity, i.e., the Bloch-Gruneisen model. Due to inherent acoustic (low-frequency) phonons ( $\omega_{ac})$ as well as high-frequency optical phonons ( $\omega_{op})$ , the contributions to the resistivity have first been estimated. The acoustic phonons of the oxygen-breathing mode yield a relatively larger contribution to the resistivity compared to the contribution of optical phonons. Furthermore, the nature of phonons changes around T = 167 K exhibiting a crossover from an acoustic to optical phonon regime with elevated temperature. The contribution to resistivity estimated by considering both phonons, i.e. $\omega_{ac}$ and $\omega_{op}$ , when subtracted from thin film data, infers a power temperature dependence over most of the temperature range. The quadratic temperature dependence of $\rho_{\it diff.} = [ \rho_{\exp} . - \{\rho_{0} + \rho_{e\text{-}ph} (= \rho_{ac} + \rho_{op}) \} ]$ is understood in terms of electron-electron scattering. Moreover, in the higher temperature limit, the difference can be varies linearly with T 4.5 in accordance with the electron-magnon scattering in the double exchange process. Within the proposed scheme, the present numerical analysis of temperature dependent resistivity shows similar results as those revealed by experiment.

Interpretation of temperature-dependent resistivity of electron-doped cuprates

The temperature-dependent normal state resistivity of single-crystal Nd1.85Ce0.15CuO4−δ is theoretically analysed within the framework of the classical electron–phonon model of resistivity, i.e. the Bloch–Gruneisen model. Due to inherent acoustic (low-frequency) phonons (ωac) as well as high-frequency optical phonons (ωop), the contributions to the resistivity have first been estimated. The optical phonons of the oxygen-breathing mode yield a relatively larger contribution to the resistivity compared to the contribution of acoustic phonons. The contribution to resistivity estimated by considering both phonons, i.e. ωac and ωop, along with the zero limited resistivity, when subtracted from single-crystal data, infers a quadratic temperature dependence over most of the temperature range (25 ≤ T ≤ 300 K). The quadratic temperature dependence of ρdiff = [ρexp − {ρ0 + ρe-ph( = ρac + ρop)}] is understood in terms of electron–electron inelastic scattering. The comparison of single-crystal experimental data with the present analysis appears to be favourable.

Interpretation of resistivity of Nd1.85Ce0.15CuO4: Electron-phonon mechanism

The temperature-dependent normal state resistivity of single crystal Nd1.85Ce0.15CuO4 − δ is theoretically analyzed within the framework of classical electron–phonon i.e., Bloch-Gruneisen model of resistivity. For the reason of inherent acoustic (low frequency) phonons (ωac) as well as high-frequency optical phonons (ωop), the contributions to the resistivity were first derived. The optical phonons of the oxygen breathing mode yields a relatively larger contribution to the resistivity compared to the contribution of acoustic phonons. Estimated contribution to in-plane resistivity by considering both phonons, i.e., ωac and ωop, along with the zero-temperature-limited resistivity, when subtracted from single crystal data infers a quadratic temperature dependence over most of the temperature range [25 ≤ T ≤ 300]. Quadratic temperature dependence of ρdiff. = [ρexp. − {ρ0 + ρe–ph (=ρac + ρop)}] is understood in terms of 3D electron–electron inelastic scattering. The comparison of single crystal experimental data appears favorable with the present analysis.

Surface Phonon Scattering in the Electrical Resistivity on Co/Ni Superlattices

The effect of surface phonon scattering on the electrical resistivity has been observed in Co/Ni superlattices, with reproducible film microstructure, independent of the film thickness. The temperaturedependent part of the resistivity increases rapidly with decreasing film thickness for films thinner than the electronic mean free path. The resistivity shows a universal behavior well characterized by the Bloch-Gruneisen model. The deviation from the bulk resistivity can be explained by a reduced surface Debye temperature and additional surface phonon modes. [S0031-9007(96)02093-5]

Precise measurements of the ab-plane resistance of YBa 2Cu 3O 7− y single crystals under hydrostatic pressure

The temperature dependence of the ab-plane electrical resistance ( R ab ( T)) of YBa 2Cu 3O 7− y single crystals has been studied under hydrostatic pressure up to 8 kbar using helium as the pressure transmitting medium. The ∂ln( ∂R ab / ∂T)/ ∂ln V value obtained by us is approximately four times greater than that calculated from the data of S.W. Tozer et al. [Phys. Rev. B 47 (1993) 8089] for the pressure range 3.6–130 kbar. The lattice Gruneisen constant (γ) estimated from our data in terms of the Bloch-Gruneisen model is unusually large, γ = 6.8.

Evaluation of physical and electrical properties of CoSi2 thin films on (100)Si grown by pulsed laser deposition

Abstract Laser physical vapour deposition (LPVD) has been used to deposit thin CoSi2 films on (100) silicon at different substrate temperatures ranging from room temperature to 600°C. Silicide films were deposited by ablating a solid target of CoSi2 in vacuum with a pulsed KrF excimer laser. Particulate-free silicide thin films were characterized by X-ray diffraction, Rutherford backscattering, and analytical and high-resolution transmission electron microscopy. We have found that films deposited at 200°C and below are amorphous; films deposited at 400°C are polycrystalline; and films deposited at 600°C are (001) textured. Resistivity of these films has been measured as a function of temperature. This plot for CoSi2 exemplifies a typical resistivity behaviour for metallic compounds. The room temperature resistivity has been found to be about 15μΩ cm with a residual resistivity of about 4 μΩ cm for these films. A theoretically based Bloch-Gruneisen model has been applied to analyse the nature of such a plo...