P. Nayak

Analysis of grains grown on fly ash treated soils

One time application of fly ash was done at the rate of 200 t/hectare in the crop lands in Odisha, India. The increase in yield of maize grains was 28% and 34% over the control values whereas the increase in yield of rice grains was 40% and 13% at Malud and Dhenkanal, respectively. The results indicated that fly ash is an amendment for soil which can improve the physical and chemical properties of deficient soil and improves the soil fertility and crop yield.

Dielectric and electrical properties of Na2Pb2La2W2Ti4Ta4O30 electroceramics

The polycrystalline sample of complex tungsten-bronze type compound (Na2Pb2La2W2Ti4Ta4O30) was prepared by a high-temperature solid-state reaction technique. Room temperature preliminary structural study using X-ray diffraction (XRD) data exhibits the formation of a single-phase new compound. The SEM micrograph of the compound exhibits non uniform rectangular grains distributed throughout the sample surface. Detailed studies of dielectric parameters (ɛr, tan δ) as a function of temperature and frequency, and P-E hysteresis (spontaneous polarization) confirmed the existence of ferroelectricity in the material. Complex impedance spectroscopy analysis, carried out as a function of frequency at different temperatures, established a correlation between the microstructure and electrical properties of the material. The electrical relaxation process occurring in the material is temperature dependent. The activation energy found from the Arrhenius plot that the conduction process in the material is of mixed type. The nature of frequency dependence of ac conductivity suggests that the material obeys Jonscher’s universal power law.

A new criterion for the mixed crystal behaviour in the diatomic linear chain model

Lucovsky, Brodsky, Burstein (LBB) have studied the behaviour of mixed crystals by setting up a criterion for the existence of local mode frequencies in real crystals starting from a diatomic linear chain model. This, while successfully predicting the one and two mode behaviour for some systems fails to predict the mixed mode behaviour. We propose a similar criterion for the existence of gap modes, by demanding that the gap mode predicted by the diatomic linear chain model should lie within the gap of the real three dimensional solid for its existence. It is shown that the gap modes for various systems calculated using this criterion are in reasonable agreement with the experimental values. The infrared behaviour of mixed crystals has to be determined by examining the existence of local as well as gap modes for the two end members of the system. This generalized new criterion successfully predicts the mixed mode behaviour of III–V mixed crystals besides predicting the one and two mode behaviour, observed in infrared absorption of mixed alkali halioes and III-V compounds.

Elemental analysis of coal and coal ASH by PIXE technique.

Coal and coal ash samples were characterized by particle induced X-ray emission spectroscopic technique. Sixteen elements, namely K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Ga, As, Rb, Sr, Y and Pb were quantified in this study. Elements like K, Ca, Ti and Fe were present as major elements, whereas, other elements like V, Cr, Mn, Co, Ni, Cu, Zn, As, Se, Rb, Sr and Pb were present in trace level. The enrichment ratio of different ash samples with respect to coal were also estimated and discussed.

ELECTRON-PHONON INTERACTION AND PHONON RESPONSE IN HEAVY FERMION SYSTEMS

The phonon response property of the Heavy Fermion (HF) systems are investigated within the Periodic Anderson Model (PAM) to explain the observed phonon anomalies. To understand the microscopic origin of these anomalies, two different mechanisms of electron-phonon interaction, namely, the usual interaction between the phonons and the electrons in the f-bands as well as the interaction due to the hybridization term of PAM, are considered. The influence of coulomb correlation U on the phonon excitation spectrum and the spectral density function are studied for various model parameters, namely, the position of the f-level E0, the ratio r of the electron-phonon coupling strengths f1(q) and f2(q), and the effective coupling strength g. The numerical evaluations of these phonon response functions are carried out for small temperatures in the long wavelength limit, while retaining terms which are linear in correlation. The observed behavior agrees well with the general features obtained in experiment.

Complex impedance properties of LiSr2Nb5O15 ceramic

The polycrystalline sample of LiSr2Nb5O15 (LSN) was prepared by a high-temperature solid state reaction technique. The impedance parameters were studied using an impedance analyzer in a wide range of frequencies (102–106 Hz) at different temperatures (28–500 °C). Nyquist plot reveals the presence of bulk effect only. The bulk resistance of the compound decreases with rise in temperature which shows the negative temperature coefficient of resistance (NTCR) like a semiconductor. The ac conductivity spectrum was found to obey Jonscher’s universal power law. DC conductivity (bulk) with temperature demonstrates that the compound exhibits Arrhenius type of electrical conductivity and the activation energy found to be 0.97 eV.

Magnetic Field Dependence of Entropy And Specific Heat of YBa2Cu3O7-delta Superconductors

The change in thermodynamic quantities (e. g., entropy, specific heat etc.) by the application of magnetic field in the case of the high-T-c superconductor YBCO system is examined phenomenological by the Ginzburg-Landau theory of anisotropic type-II superconductors. An expression for the change in the entropy (Delta S) and change in specific heat (Delta C) in a magnetic field for any general orientation of an applied magnetic field B-a with respect to the crystallographic c-axis is obtained. The observed large reduction of specific heat anomaly just below the superconducting transition and the observed variation of entropy with magnetic field are explained quantitatively.

Concentration dependence of the mixed crystal modes of vibration

The concentration dependence of the reststrahl absorption in various mixed crystals exhibiting one, two and mixed mode behaviour is investigated using the coherent potential approximation (cpa). The phonon Green’s function, the impurity mode frequencies and the strength of absorption are calculated in the Einstein model from the generalizedcpa proposed by Tripathi and Behera which takes into account both mass and force constant changes. The introduction of a phenomenological concentration dependence of the force constant change parameter is shown to provide a satisfactory explanation of the concentration dependence of the experimental data for the twenty mixed crystal systems analysed. It is conjectured that the nearest neighbour force constant of an impurity atom substituted at a host site is very much different from that of a perfect crystal consisting of these impurity atoms and that both these play an important role in determining the one, two and mixed mode behaviour of the mixed crystals.

Size‐Dependent Cohesive Energy and Melting Of Non‐Spherical Nanoparticles

All most all theoretical models assume spherical nanoparticles. However, thermodynamic properties of non‐spherical nanoparticles are the subject of recent interests. In this article, we have discussed the size‐dependent cohesive energy and melting of non‐spherical nanoparticles based on liquid‐drop model. The surface to volume ratio is different for different shapes of nanoparticles and as a consequence, the variation of cohesive energy and melting of non‐spherical nanoparticles is different from that of spherical case. By analyzing the reported experimental results, it has been observed that liquid‐drop model can be used to understand the size‐dependent cohesive energy and melting of non‐spherical nanoparticles.

INFLUENCE OF ELECTRON–PHONON INTERACTION ON EFFECTIVE MASS IN SOME HEAVY FERMION (HF) SYSTEMS

It is a fact that for ordinary metals, the electron–phonon interaction increases the quasi-particle mass, which is in contrast to the finding by Fulde et al. that, for some heavy Fermion (HF) systems, it decreases. Some experiments on HF systems suggest that there exists a strong coupling of the elastic degrees of freedom with these at the electronic and magnetic ones. To understand the effect of electron–phonon interaction on effective mass, the electron–phonon coupling mechanism in the framework of the periodic Anderson model is considered, and a simple expression is derived. This involves various model parameters namely, the position of the 4f level; the effective coupling strength, g, temperature, b; and the electron–phonon coupling strength, r. The influence of these parameters on the value of effective mass is studied, and interesting results were found. For simplicity, the numerical calculation is performed in the long wavelength limit.