008897   Kaatze U (Drittes Physikalisches Institute, Georg-August-Universitat, Friedrich-Hund-Platz 1, 37077 Gottingen, Germany, Email: uka@physik3.gwdg.de) : Ultrasound techniques for characterizing liquids I. broad-band spectrometere. J pure appl Ultrasonics 2009, 31(1), 1-12.

This tutorial gives a short introduction into the broad-band ultrasonic spectroscopy of liquids. The fundamentals of acoustical methods are. summarized. Preference is given to methods using continuous waves and pulse modulated signals. Related techniques, such as time-domain methods with step-like excitation of the sample and with optical monitoring of acoustical waves (Brillouin scattering), are briefly mentioned, too. Constructions of some types of sonic cells for liquids and electronic set-ups for spectral measurements are presented in detail. The merits and limitations of different techniques of measurements, covering the frequency range from almost 10 kHz up to nearly 10 GHz, are discussed. Together with applications in the relaxation properties of liquids, examples of broadband ultrasonic spectra are shown.

10 illus, 51 ref

008896   Joseph A;Sharma G K;Jay Kumar T (Non-Destructive Evaluation Div, Indira Gandhi Centre for Atomic Research, Kalpakkam-603 102, Email: tjk@igcar.gov.in) : Ultrasonic internal rotary inspection system (IRIS) for heat exchanger and steam generator tubes. J pure appl Ultrasonics 2009, 31(1), 24-30.

Ultrasonic Internal Rotary Inspection System (IRIS) is used for inspection of tubes of heat exchangers and steam generators. The system displays circumferential cross section of tubes (wall thickness of tubes) at any given axial position and reveals both uniform and localised (pitting) corrosion. The operating principle of IRIS and comparison of wall thickness measurements by physical and IRIS methods are briefly explained. Details of studies carried out on the resolution capabilities of IRIS in stainless steel and brass tubes having artificial defects (holes) are discussed. The results obtained from a study carried out on a carbon steel tube with artificial defects under baffle plate are also discussed in this paper.

13 illus, 2 tables, 3 ref

008895   Jagtap U S;Sharma A K;Patil P T (Physics Dep, Dhanaji Nana College, Fizpur-425 503) : Signature of plasma depletions using OI 630.0 NM nightglow observations from 17°N latitude. Asian J chem envir Res 2010, 3(4), 70-3.

Regular Night Airglow observations were made from Kolhapur, a low latitude station (16.8° N; 74.2° E) in India on clear moonless nights using tilting photometers to map the thermospheric motion and to study the low latitude ionospheric irregularities by measuring the nightglow signatures at 630 nm. The photometers are portable and can be directed to any desired point in the sky (Zenith, 30° East, and 30° North of zenith direction). The results show that the airglow structures are north-south aligned and moves eastward; zonal wind computed from the HWM 93 model matches well with observed velocities. The depletions were normally confined to the time between 20:30 and 01:00 1ST. The results validate the earlier results from India and elsewhere.

4 illus, 7 ref

008894   Gogoi A;Choudhury A;Stanciu G A;Ahmed G A (Physics Dep, Tezpur Univ, Optoelectronics and Photonics Laboratory, Tezpur-784 028) : Construction of a multidetector array incorporated laser-based scattering system for ultrafine TiO₂ characterization. J Optics 2009, 38(2), 67-74.

A laser based light scattering system has been designed and fabricated for measuring the scattering properties of ultrafine TiO₂ particles as a function of scattering angle at the He-Ne laser wavelength 632.8 nm. The system essentially consists of an array of 16 highly sensitive static Si detectors (BPW34) which can measure scattered light signals from 10 degrees to 170 degrees in steps of 1 degree. The signals are interfaced to a high gain 16 channel preamplifier and a dedicated data acquisition system (Vinytics PCI-9812) for data analysis. The measured scattering properties of rutile (TiO₂) particles agree reasonably well with the theoretical results drawn from T-matrix calculations.

2 illus, 1 table, 20 ref

008893   Ghatak B;Mandal J (Univ Dep of Physics, T M Bhagalpur Univ, Bhagalpur-812 007) : Anlaysis of interionic potentials in chalcogenide crystals with sodium chloride structure. J Indian Chem Soc 2009, 86(12), 1271-79.

Values of cohesive energy, atomization energy, force constant, IR absorption frequency, Debye temperature, Griineisen parameter, Anderson-Griineisen parameter and Moelwyn-Hughes parameter for 45 chalcogenide crystals of NaCl-structure are reported here. These parameters have been obtained by using the Born-Mayer and Varshini-Shukla interionic short-range repulsive interactions. Calculations have also been performed for the computation of first order volume dependence of Griineisen parameter commonly known as second Griineisen parameter using expressions of higher order derivatives of interaction potential within the frame work of Dugdale and MacDonald theory. The high pressure behaviour of these crystals have also been studied.

6 illus, 3 table, 22 ref

008892   Garai S K;Mukhopadhyay S (Physics Dep, M.U.C. Women's College, Burdwan, West Bengal-713 104) : Method of implementation of all-optical frequency encoded logic operations exploiting the progagation characters of light through semiconductor optical amplifiers. J Optics 2009, 38(2), 88-102.

Optics has already proved its strong potentiality for conducting parallel logic, arithmetic and algebraic operations. Since last few decades so many all-optical data processors were proposed. To implement these processors different encoding / decoding techniques, such as polarization encoding, intensity encoding, phase encoding technique have been reported. Very recently 'frequency encoding' technique have drawn a special interest to the scientific community. The frequency is the fundamental character of a signal and it preserves its identity irrespective of reflection, refraction, transmission, absorption throughout the communication. Therefore, if two specific frequencies are encoded as 1 state and 0 states respectively, then one can ensure about the state of information throughout the communications. In this paper the authors propose a method of conducting inversion OR, NOR and NAND logic operations exploiting the wavelength conversion, which is achieved by exploiting the cross gain modulation (XGM) property of reflecting semiconductor optical amplifier (RSOA), as well as the property of change of nonlinear rotation of the state of polarization of probe beam by cross phase modulation (XPM). Both the wavelength conversion properties arc controlled by the intensity of the pump beam. The major advantage of SOA-switching over any other conventional switching is that SOA-switching require low power with good on off contrast ratio. Again as the NAND and NOR are the universal logic gates, so any other logic operation can be implemented using this concept.

5 illus, 3 table, 22 ref

008891   Dutta N;Mohanta D;Sulania I;Choudhury A (Physics Dep, Tezpur Univ, Nanocience Laboratory, Napaan Sonitpur, Assam) : Optical properties and SHI irradiation on PbS sensitized nanoporous TiO₂ network. J Optics 2009, 38(3), 169-76.

Titania is a well-known oxide system intended for use in a wide variety of applications. Nanocrystalline titania can be deposited on substrates in the form of thick and thin films. This paper studies the PbS nanoparticle growth in nanoporous network of TiO₂ along with its promising properties after incorporation of PbS nanoparticles. PbS nanoparticles are ultra small particles, with dimension 1-100 nm, exhibit discrete electronic states along with other interesting properties. Due to extremely large surface-to-volume ratio (<62><62>1), nanoparticle possess inherent defect sites in the form of intermediate states/surface states located in the forbidden gap. When one nanoparticle system is clubbed with another nanoparticle system then it is most likely to exhibit typical phenomena where electron can tunnel from one particle to the other. Formation of PbS quantum dots was analyzed by SEM, AFM, XRD, TEM and PL. Controlled heating effect is studied if there is any change in structure of this system. Interfacial charge transfer between the surface states of PbS and TiO₂ was studied through comparative photoluminescence of this system. Results obtained from these studies infer that the coupled system of PbS/TiO₂ can be made useful for single electron devices, quantum point contacts and other optoelectronics applications.

9 illus, 17 ref

008890   Chaudhari K S;Toda Y R;Jain A B;Gujarathi D N (NO, S.V.S.'s Arts and Science College, Dondaicha-425 408) : Synthesis and electrical properties of PbSe thin films deposited by physical evaporation technique. Asian J chem envir Res 2010, 3(4), 30-4.

PbSe thin films were prepared on glass substrate by physical evaporation technique at a pressure of 10^-5 torr. The resistivity of the films is determined over the thickness range of 1000 °A, 1500 °A, 2000 °A, and 2500 °A. The temperature dependence of resistivity-shows semiconductig behaviour at temperature below 453 K. The thickness dependence of resistivity is found to follow size effect theory. Activation energy is found to be 0.0831 to 0.0265 eV. Hall coefficients, Hall mobility, charge carrier concentration was also determined. The Hall coefficient shows a positive sign exhibiting P- type nature of films. The x ray diffraction analysis confirms that deposited films are polycrystalline having cubic structure.

5 illus, 1 table, 23 ref

008889   Chakraborty S;Bera S C (Electrical and Electronics Engineering Dep, Birla Institute of Technology, Mesra, Ranchi-853215, Email: sarbaniry@yahoo.com) : Interaction of polarized beam with copper surface and its application for metal-dielectric discrimination of vero board. J Optics 2009, 38(1), 1-15.

The state of polarization of a specularly reflected beam from metal and dielectric surface is mainly dependent on the optical constants of the materials, wavelength of the illuminating beam, state of polarization and angle of incidence of the incident beam. In the present study the state of polarization of the reflected beam is analyzed with the help of Stokes formalism where the input beam is linearly polarized. The intensity variation of the reflected beam passing through an analyzer is then studied by varying the orientation of the transmission axis of the analyzer and acquiring the image of the metal-dielectric (copper film deposited on microscope slide) surface for each angular position of the analyzer. The degree of linear polarization (DOLP) as well as fractional non-linear polarization (FNLP)of the image of the metal-dielectric surface is evaluated both theoretically and experimentally and for both monochromatic and polychromatic incident illumination. A good agreement is observed between theoretical and experimental results. For estimation of pixel-wise variation of DOLP and FNLP of the metal dielectric surface, the spectral Stokes parameters for each pixel location are computed with the help of measurement matrix. As a practical application of the study, a printed circuit board (vero board) is used as a metal-dielectric (perforated copper strip on glossy dielectric substrate) surface for observing pixel-wise DOLP and FNLP variation. The resultant DOLP and FNLP images for Vero board show the metal-dielectric discrimination capability under polychromtic illustration.

4 illus, 1 table, 35 ref

008888   Bhatnagar V P;Tan A (Physics Dep, Alabama A & M Univ, Normal, AL 35762, USA, Email: vinbhatnagar@hotmail.com) : On the energetics in the lower thermosphere. Indian J Radio Space Phys 2010, 39(4), 189-93.

The resultant global mean heating rate due to solar EUV radiation in presence of the infrared cooling from the gases like carbon dioxide, nitric oxide and the atomic oxygen has been estimated in the altitude range 120 - 200 km for different solar activity and seasons at moderate latitudes utilizing MSIS-E models. The simplified energy equation leads to a peak height in the heating/cooling rates and a direct dependence of the exospheric temperature on these rates at the lower thermospheric boundary. The computations are performed mainly for quiet periods and steady state noon time maximum and nighttime minimum conditions, when the temperature variation with local time can be ignored. The increase in cooling rates in the lower thermospheric heights from increased densities tends to pull the exospheric temperature down and vice versa. However, during daytime the relative magnitudes of the heating and cooling rates determine the decrease in exospheric temperature. It is shown that ideally the heating/cooling rates above their peaks decrease with height exponentially [exp(- s (z - Zg)), where, z, is the height; z₀), the lower boundary; and s, a parameter dependent on the temperature profile and can be easily estimated from any model or observed temperatures. The case studies show that the resultant heating/cooling rates increase with increase in the solar activity/temperature irrespective of the season by a factor of about 2 from the minimum to maximum solar activity. The seasonally averaged heating rate values for daytime and nighttime at the peaks for moderate solar activity of about 0.7 x 10^-7 and 0.9 x 10^-7 (ergs cm^-3 s<^-1), respectively agree well with the existing theoretical and observed values. Above the peaks, the resultant average cooling rates during nighttime for quiet periods are larger by a factor of 2 to 8 depending on the solar activity from the observed ones just for nitric oxide by SABER instrument. This is probably due to the fact that SABER values include all local times, seasons, latitudes, longitudes and geophysical activities and does not include the main constituent, the atomic oxygen. The changes in the cooling rates from increased CO₂ and CH₄ could imply corresponding change in the atmospheric densities originating from related changes in the exospheric temperatures with resulting feedback to the cooling rates and subsequent density changes.

5 illus, 21 ref

008887   Banerjee S;Sarmah S;Ashok Kumar (Physics Dep, Tezpur Univ, Material Research Laboratory, Tezpur-784 028) : Photoluminescence studies in HCl-doped ployaniline nanofibers. J Optics 2009, 38(2), 124-30.

In the present work polyaniline (PAni) nanofibers have been synthesized by interfacial polymerization technique. Pellets are made from PAni nanofibers and characterized by XRD, TEM, UV-Vis spectroscopy, Photoluminescence spectroscopy and Four-probe conductivity measurements. XRD results show the increase in the degree of crystallinity with the increase of concentration of dopant acid. It also shows peak broadening, which indicates reduction of fiber diameter with increasing dopant concentration. TEM micrograph confirms the formation of PAni nanofibers of diameter around 20-30 nanometer. The UV-Visible spectra show three prominent peaks at 320nm, 430nm and 800nm, which confirm the formation of a single broad polaronic band in the band-gap of the PAni nanofibers. Four-probe measurements show that the electrical conductivity of PAni nanofibers increases with doping. PL spectra show a broad peak in violet region (λ = 405 nm) and indicate a decrease of fiber diameter with the increase in HCl concentration.

4 illus, 1 table, 13 ref

024729   Shirage P M;Jadhav A B;Pawar S H (Superconductivity Lab. Sch of Energy Studies. Dep of Phys, Shivaji Univ, Kolhapur-416 004) : Thickness dependent transport properties-of TI-2223/Al hetero-nano structures. Indian J Cryogenics 2003, 28(3), 103-10.

Some attempts were made to form a pathway to high T_c and J_c using the superconducting hetero-nano structure of TI₂Ba₂Ca₂Cu₃O₁₀/Al (TI-2223/Al). In continuation of this work this paper reports the thickness dependent transport properties of TI-2223/AI hetero-nano structure. The TI-2223 films were electro-deposited onto the Al-coated glass substrate at - 2.25 V vs SCE. By varying the deposition time, the thickness of the TI-Ba-Ca-Cu alloyed films was varied from 0.5 to 3 mm followed by the electrochemical oxidation at + 0.7 V vs SCE for 25 min. to transform these into superconducting state. The electrodeposition mechanism of nucleation process was studied by chronoamperometry by plotting the (I/I _max)^-2 vs (t/t_max) and comparing it with the theoretical equations. The nucleation process was found to be progressive with nano size spherical granules ( 32 nm ) deposited onto the Al-coated glass substrate. The films were characterized by the XRD, SEM and EDAX. The XRD characterization shows the formation of the single phase tetragonal TI-2223 superconductor. The calculated lattice parameters were a = 3.85 A and c = 35.71 A. The SEM images show nano-size grains with high density and low porosity without any pin holes. The transport properties such as T_c and J_c values of these films were studied by standard four-probe technique. T_c was found to be the function of the thickness

13 illus, 3 tables, 8 ref

024728   Ray S (NO, , 7, Sardar, Shankar Road, Kolkata-700 026) : Crystallography at moderately low temperatures-experience with some phase transition. Indian J Cryogenics 2003, 28(2), 37-43.

X-ray diffraction photography with single crystal samples maintained at specified low Temperatures is an important technique for studying structural changes after phase transition. Fabrication of simple and inexpensive attachments for different types of X-ray cameras, for maintaining a fixed low temperature of the sample, using cooled stream of nitrogen gas, is described. Use of these attachments is illustrated in cases  of structural study of transformed phases in different single crystals.

2 illus, 8 ref

024727   Prakash S;Mehrotra I (Dep of Phys, Univ of Allahabad, Allahabad-211 002) : Ground state proton radioactivity in proton rich nuclei. Proc Natn Acad Sci India-Sect A 2006, 76(1), 75-8.

Half-lives for proton emission from ₅₁Sb¹⁰⁵, ₅₃I¹⁰⁹, ₅₅Cs¹¹², ₅₅Cs¹¹³ proton rich nuclei have been calculated by using Becchetti - Greenless potential in the WKB appioximation method. It is observed that good agreement with the experimental data is obtained in this simple one body approach to the tunneling problem. Results are compared with those obtained for a square well potential. Variation in the values of half-life with spectroscopic factor has also been studied.

3 illus, 1 table, 10 ref

024726   Pradhan J;Naser M Z A;Bhunia U;Sarkar A; Bhattacharjee T K;Paul S;Banarjee A;Sur A;Saha S;Rangnathan R; Bhandari R K (Variable, Energy Cyclotron Cent, 1/AF Bidhan Nagar, Kolkata-700 064, Email: jpradhan@veccal.emet.in) : Measurement of critical current and joint resistance of superconducting wire used for K-500 superconcducting cyclotron magnet coil. Indian J Cryogenics 2003, 28(1), 34-6.

An Experimental set up has been developed for the electrical characterization of NbTi mulmilamentary composite wires at liquid helium temperature. The wire is being used to make K500 superconducting cyclotron magnet coil. Test has been carried out to measure critical current and joint resistance between two superconductors under magnetic field up to 7 Tesla. Test results show high critical current density with good filament uniformity indicated by its high quality index. Joints are made in-house on coil winding machine and test results indicate that they have acceptably low resistance and carry sufficient current.

3 tables, 4 ref

024725   Pal S;Chaudhuri B K;Neeleshwarm S;Chen Y Y; Yang H D (Dep of Solid St Phys, Indian Ass for The Cultivation of Sci, Kolkata-700 032) : Effect of Pb doping in the transport and magnetic properties of the metallic La_1-x Pb_x NiO₃ (0.0 <60> x <60> 0.1) oxide. Indian J Cryogenics 2003, 28(4), 116-21.

Transport properties (conductivity and thermoelectric power) of Lai_xPb_xNiO₃ (0.0 ≤ x <60> 0.1) show metallic behaviour for a wide range of temperature (10-550K). A decrease in the paramagnetic susceptibility (χ) is observed with Pb doping. Above 50K susceptibility (%) is almost temperature independent and exhibits Pauli like behaviour with a small additional ∧ Curie law contribution. Resistivity (ρ) which increases with Pb doping shows a T^1.5 dependence at tower temperatures (below 15GK). A linear T dependence of resistivity observed at higher (above 150K) temperatures suggests the importance of electron-phonon (el-ph) interaction. The el-ph interaction constant (λ) increases (0.80 to 2.53) with Pb doping (x = 0.0 to 0.1).

5 illus, 14 ref

024724   Mukherjee S;Samanta R;Pal A K (Dep of Solid St Phys, Indian Ass for the Cultivation of Sci, Jadhavpur, Calcutta-700 032) : EPR studies on VO<. Indian J Cryogenics 2003, 28(2), 47-50.

X-band EPR studies on VO²⁺ doped silica glasses at room and LN₂ temperatures have been reported. Monolithic silica gels doped with two different VO²⁺ mol% concentrations (0.2 and 2.0) are prepared by sol-gel method. Gels, after drying at room temperature for 4-6 weeks, are calcined at several temperatures up to 965°C. 0.2 mol% VO²⁺ doped glass samples calcined at 430°C and 625°C exhibit isotropic hyperfine VO²⁺ EPR spectra at room temperature (RT) which become anisotropic at liquid nitrogen temperature (LNT). At both room and LN₂ temperatures hyperfine structure is absent for 860°C and 965°C calcined glass samples. Instead, a very broad signal having line-width ΔHpp - 600 mT is observed. For 2.0 mol% VO²⁺ doped glass, EPR observations are more or less similar. The only difference is that in this case hyperfine structure disappears for samples calcined at 900°C and the line-width of the broad line is comparatively much less (250 mT). The results have been discussed in the light of porous structure of silica glass and formation of vanadyl clusters as a consequence of disruption of silica pores at high calcination temperatures.

2 illus, 15 ref

024723   Kumar M;Nath G (Dep of Math, Indian Inst of Sci, Bangalore-560 012, Email: mkumari@math.iisc.ernet.in) : Unsteady MHD stagnation flow over a moving wall. Proc Natn Acad Sci India-Sect A 2006, 76(1), 69-74.

The unsteady viscous stagnation flow of an electrically conducting fluid over a continuously moving wall with an applied magnetic field has been investigated when the free stream and wall velocities increase arbitrarily with time. The flow is initially (t = 0) steady and at time t <62> 0, it becomes unsteady. The semi-similar solution of the unsteady Navier-Stokes equations along with the energy equation governing the flow and heat transfer has been obtained numerically. Also the self-similar solution is obtained when the surface and free stream velocities vary inversely as a linear function of time. The shear stress and the heat transfer increase with time and magnetic field. The surface shear stress vanishes for certain value of the ratio of the wall velocity to the free stream velocity.

3 illus, 1 table, 24 ref

024722   Joshi K B;Sharma B K (Dep of Phys, Coll of Sci Campus M.L. Sukhadia Univ, Udaipur-313 001, Email: k_joshi@yahoo. com ) : Compton profile study of AlAs and AlP by empirical pseudopotential method. Proc Natn Acad Sci India-Sect A 2006, 76(1), 79-83.

Directional Compton profiles of AlAs and A1P have been calculated employing the local empirical pseudopotential method using the 10-points and 60-points schemes. The results are discussed in terms of anisotropies in the directional Compton profiles along [100], [110] and [111] directions. The nature of bonding in the two compounds has also been discussed in terms of simplified equal valence electron density profiles.

5 illus, 1 table, 16 ref

024721   Jadhav A B;Pawar S H (Sch of Energy Studies. Dep of Phys, Shivaji Univ, Kolhapur-416 004) : Recent advances in development of (MgB₂) superconductor for applications. Indian J Cryogenics 2003, 28(3), 90-102.

The serendipitous discovery of MgB₂ superconductor with T_c = 39 K by Akimitsu's group in January 2001 has sparked a race to uncover its basic properties and to find its suitability towards large scale application to realize the dream of human being, it has twice the critical temperature (T_c) value compared to those of other simple intermetallic compounds. However, this high value of T_c is not the only sufficient criteria for its large scale applications, but also it is essential to enhance the flux pinning and increase the critical current density in high fields to the level attained by the conventional low T_c superconductors like NbTi and Nb₃Sn. Recently, a J_c of 3000 A/cm^-2 is achieved in 8 T at 5 K for the Si - doped MgB₂ one order of magnitude higher than the control sample. The value of H_c2 as high as 18 T has been achieved recently. For commercial applications of superconductors, the easy method of synthesis with low energy inputs, environment friendly process, ease of operation of devices, durability'and reproducibility are some of the key requirements. Towards these objectives, the group headed by one of the authors (S.H.P.) has made some pioneering work on MgB₂ superconductors and reported their results in the recent issue of Superconductor Science and Technology, 2003. The development of superconducting MgB₂ pancake coils with electrochemical complex technique to generate high magnetic fields has been attempted. The review of all these recent advances in development of MgB₂ superconductors for practical applications has also been incorporated in the present paper.

5 illus, 78 ref

024720   Dole B N;Sah S S (Dep of Phys, JES Coll, Jaina-431 203) : The major role of ionicity in Y/Pr-123 high temperature superconductors. Indian J Cryogenics 2003, 28(3), 73-8.

Investigated Y_1-xPr_xBa₂Cu₃O_7-δ system of high temperature superconducting compounds. The samples or the system Y_1-xPr_xBa₂Cu₃O_7-δ with compositions x = 0.0, 0.1, 0.2, 0.3, 0.4 & 0.5 were prepared by chemical route. This system attracts lot of attention of researchers, scientists and theorists due to the anomalous behavior of Pr in Y-123 compounds. The system is studied thoroughly but no unique result is quoted yet. There is controversy about the valency of Pr i.e. whether it is in 3+ state or 4+ state or intermediate state. The substitution of Pr in Y-123 compounds suppresses the T_c monotonically and however, other rare earths do not affect superconductivity significantly. The Pr is the exception for this and plays very interesting role in system. Analyzed the samples by X-ray diffraction, and have found ionicity. Ionicity results show that Pr is in 3+ state rather than in 4+ state and it may be the possible cause for the suppression of T_c in Pr substituted Y_1-xPr_xBa₂Cu₃O_7-δ compound. The annihilation of superconductivity in Pr substituted YBCO compounds due to hole filling or hole localization or magnetic pair breaking.

8 illus, 4 tables, 9 ref

024719   Dey A K;Banarjee D;Pal A K;Bhattacharya R (NO, Prabhat Kumar Coll, P.O. Contal, Purba Medinipur-721 401) : Thermoelectric power of single crystals of doped bismuth. Indian J Cryogenics 2003, 28(2), 59-61.

Thermoelectric power of single crystals of bismuth doped with indium and gallium has been measured as function of temperature between 100 and 300K. Thermoelectric power is negative throughout the whole range of temperature investigated for all the samples. This confirms the predominant contribution of electrons towards the thermoelectric power because of the presence of sufficient number of electrons at the low temperature investigated (-100K) and their higher mobility over that of the holes.

2 illus, 1 table, 7 ref