S. V. Suryanarayana

The high-temperature thermal expansion of Ni3Al measured by X-ray diffraction and dilation methods

The lattice parameters of Ni3Al have been determined accurately for the temperature range 25 to 594 degrees C by a high-temperature X-ray powder diffraction method. These data are used to evaluate the coefficients of thermal expansion at various temperatures. The thermal expansion of Ni3Al has also been measured from 25 to 1000 degrees C by a dilation method. The thermal expansion values obtained by the dilation method are in good agreement with those determined by the X-ray diffraction method at around room temperature, but the agreement deteriorates with increase in temperature.

ELECTROMECHANICAL COEFFICIENTS OF MAGNETOELECTRIC PZT–CoFe2O4 COMPOSITE

The magnetoelectric property of composite materials consisting of piezoelectric and piezomagnetic constituents are of interest since the stresses induced in them on application of an external magnetic field are converted into electrical signals. The electrical output is primarily due to electromagnetic coupling between the two participating phases. The present paper deals with the evaluation of the electromechanical coupling in the magnetoelectric composite consisting of 50% lead zirconate titanate (Pb0.96Sr0.04Ti0.47Zr0.53O3) and 50% CoFe2O4, the composition having maximum magnetoelectric conversion efficiency. A sum rule is proposed to calculate the electromechanical coupling coefficient and the results are correlated with the experimental data.

Magnetoelectric properties in NCMF/PZT particulate and bulk laminate composites

Particulate composites and bulk laminates of Ni–Co–Mn ferrite (NCMF) and lead zirconate titanate (PZT) were synthesized by the solid state synthesis route. The magnetoelectric (ME) particulate composites with (x)NCMF + (1 − x)PZT (x = 0, 0.5, 0.6, 0.7 and 1) have been synthesized to study the effect of the PZT mole fraction on the ME output in particulate composites. The presence of two phases in the particulates was confirmed by XRD and SEM. The geometry of the bulk laminate samples being NCMF–PZT–NCMF alternate layers, ME measurements were carried out on both particulate and laminates using the dynamic ME set-up. The ME output is found to vary with the PZT mole fraction in the particulates and with the thickness ratio in the laminates. The particulate composite with 0.6 NCMF + 0.4 PZT revealed an ME output of 741 mV cm−1 at a fixed 64 Oe (1.008 kHz) ac magnetic field and a 0.7 kOe dc bias field. For the laminate composites the ME output as a function of the thickness ratio and the dc and ac magnetic fields has been studied. The highest ME output of 3.53 V cm−1 was observed at a fixed ac magnetic field of 64 Oe (1.008 kHz ac frequency) for the 2–2 laminate sample. The ME coefficient (α) was calculated for the samples. It is observed that the ME output is higher in the laminate composites when compared with the particulate composites due to higher mechanical coupling and better stress transfer between the phases.

Synthesis and Electrical Properties of SmBi5Fe2Ti3O18

SmBi5Fe2Ti3O18, a five layered bismuth oxide compound is synthesized using a solid-state double sintering method. DC conductivity, impedance, and AC conductivity are studied in the temperature range 30–500°C and frequency range 1 kHz–1 MHz. Complex impedance plots are used to separate grain and grain boundary contributions to electrical impedance. Activation energy for DC conductivity was found to be around 1.0 eV. The results are analyzed to understand the conductivity mechanism.

Synthesis and Characterisation of 1-x (Na1/2Bi1/2TiO3)-x(BiFeO3) Ceramics

Ceramic samples of the series 1-x (Na 1/2 Bi 1/2 TiO 3 )–x (BiFeO 3 ) were made using a conventional solid state sintering technique. X-ray diffraction studies reveal their rhombohedral symmetry at room temperature. Temperature and frequency dependant dielectric measurements show that the transition temperature (Tc) shifts towards higher temperatures as the content of BiFeO 3 is increased. The pyroelectric measurements show that the samples are ferroelectric. The samples also show magnetoelectric output.

Comparison of electrical and dielectric properties of BLSF materials in Bi-Fe-Ti-O and Bi-Mn-Ti-O systems

Compounds having the BLSF structure are interesting in view of their ferroelectric properties and also various applications. These are Aurivillius phases having the general formula (Bi2O2)2+ (An−1BnO3n+1)2− where A represent the 12-fold coordinated cation with low valancies in the perovskite sub lattice; B denotes the octahedral site having ions of high valancies and n is the number of perovskite layers between the (Bi2O2)2+ layers along the c-axis. A number of compounds in the system Bi─Fe─Ti─O have been synthesized in our laboratory and studied earlier for their electrical, dielectric, magnetic and magnetoelectric properties. By replacing Fe with Mn, we have synthesized Bi5MnTi3O15, Bi6Mn2Ti3O18, Bi7Mn3Ti3O21, Bi8Mn4Ti3O24 and Bi9Mn5Ti3O27. These compounds have been studied for their structure, electrical, dielectric and pyroelectric properties. This paper reports the data on the physical properties of Mn containing compounds and a comparison is made with those similar compounds having Fe.

Elastic anomalies in sodium-doped Bi-2212 single-phase HTSC materials

A series of sodium-doped Bi-2212 single-phase high- superconductors have been prepared by the solid state reaction method. After the usual characterization by XRD, SEM, bulk density porosity etc, ultrasonic longitudinal velocity studies were undertaken over the temperature range 80 - 300 K using the pulse transmission technique. In the temperature range 300 - 230 K, in contrast to normal solids, the velocity of Bi - Na(0) and Bi - Na(3) samples is found to decrease with decreasing temperature (elastic softening) followed by a velocity maximum at around 150 K for all the four samples, signifying the presence of lattice instabilities. Plausible explanations are given for both the elastic softening and the velocity maxima on the basis of microstructure and ordering readjustments of the oxygen atoms among the Cu - O planes of the samples.

High temperature thermal expansion characteristics of Ni3Al alloys

The thermal expansion of Ni3Al alloys with and without ternary additions have been investigated with the aid of a dilatometer. The Ni3Al alloys were studied over the temperature range 25–1000 °C. The coefficient of thermal expansion α of all the aluminides studied in this investigation varies linearly with the temperature. The coefficient of thermal expansion of Ni3Al is found to show an increase with the decrease in Al content from stoichiometric composition. B and Zr additions decrease the value α of Ni3Al alloys at room temperature while Hf and Ti additions do not alter it significantly.

Thermal expansion characteristics of Ti3Al and the effect of additives

Abstract A perusal of the literature indicates that there exist significant differences in the data on the coefficients of thermal expansion α of Ti3Al. While X-ray studies indicate an increase in the values of a with temperature, the dilatometric data had shown an anomalous variation in the intermediate temperature ranges. In view of the discrepancy existing between these data and also to study the influence of the alloying element on physical and mechanical properties of Ti3Al, determination of the thermal expansion coefficients of stoichiometric Ti3Al, Ti3Al-5at.%Nb and Ti3Al-7.5at.%Nb and microhardness measurements of these alloys have been undertaken. The effect of heat treatment on the thermal expansion coefficients of Ti3Al-5at.%Nb and Ti3Al-7.5at.%Nb is studied in the present investigation. The variation in the thermal expansion coefficient with the radius ratio of titanium to that of the additive element is examined.

Debye temperature and mean-square amplitudes of vibration of Ti3 Al alloys

The meagre experimental data on the physical properties of titanium aluminides, in particular on the alloys belonging to the Ti3Al phase, has prompted the authors to undertake a detailed study of these alloys. In this paper, Debye temperatures and mean-square amplitudes of vibration of four single-phase Ti3Al alloys of composition 22.5, 25.0, 30.0 and 33.0% aluminium are presented. The root-mean-square amplitudes of vibration of stoichiometric Ti3Al are compared with those of other metals having hexagonal-close-packed structures. The variation of the Debye temperature with the percentage of aluminium is also discussed.