• Volume 4, Issue 1

      March 1982,   pages  1-51

    • Structural and electrical properties of the system ZnFeMnO4 - GaCoMnO4

      P S Jain V S Darshane

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      X-ray crystallographic and electrical conductivity studies of the system ZnFeMnO4 - GaCoMnO4 were carried out with a view to investigating the cation distribution. The system is tetragonal in the range of 0⩽x⩽20 and cubic in the range 40⩽x⩽100 (wherex denotes the mole percentage of GaCoMnO4). The plot ofV1/3vs composition shows a break at the transition region. The value of oxygen ion parameter (u) decreases with increase in concentration of a8G+ atA-site. The electrical resistivity-temperature behaviour obeys Wilson’s law. Thermoelectric coefficient (α) values vary between 37 and 230μV/K. The mobility of holes calculated from IR and conductivity data is of the order of 10−9cm2/V-sec. X-ray intensity calculations and conductivity measurements suggest the ionic configuration of the system to be, Zn1−x2+Gax3+ [Fe1−x3+ Cox2+ Mn3+]O42−

    • Spin-state equilibria in YbCoO3

      D Bahadur

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      The relative properties of high spin and low spin Co8+ in HoCoO3, ErCoO3 and LuCoO3 are about 1 : 1 above a characteristic temperature. YbCoO3 seems to show a similar behaviour with no evidence of electron transfer between the high spin and low spin states.

    • Dispersion of dielectric constant and resistivity of Cux Zn1−x Fe2O4 samples

      S R Sawant R N Patil

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      Cux Zn1−x Fe2O4 samples exhibit dispersion of dielectric constant, tanδ and resistivity in the frequency range of 1 kHz to 50 MHz. The dispersion exhibited is in general accord with Koops’ model. However, the details of the conducting and non-conducting regions must be taken into account when composition tends to change interrelationship between the elementary capacitor resistor circuits.

      On quenching these samples from 800°C the dielectric constantε1 showed an increase for CuFe2O4 and Cu0·8Zn0·2Fe2O4 samples. The dielectric constant of the remaining samples showed no influence on quenching. The compositional variation showed that the dielectric constant has higher value for the ferrite Cu0·4Zn0·6Fe2O4

      The results are explained on the basis of cation transfer.

    • Dielectric properties of K2Zn2(SO4)3 and (NH4)2 Mg2(SO4)3

      Prameela Devi Lalitha Sirdeshmukh

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      Dielectric constant (ɛ), dielectric loss (tan δ) and conductivity (σ) for K2Zn2(SO4)3 and (NH4)2 Mg2(SO4)3 have been measured over the frequency range 100 Hz — 100 kHz and in temperature range 30°C — 400°C. The values of static dielectric constant at room temperature are 7.67 and 4.80 for K2Zn2(SO4)3 and (NH4)2 Mg2(SO4)3 respectively. The plots of log σ against reciprocal temperature at different frequencies of these samples merge into a straight line beyond 250°C and the activation energies calculated in this region are found to be 0.67 eV and 1.98 eV for K2Zn2(SO4)3 and (NH4)2 Mg2(SO4)3 respectively.

    • Temperature dependence of vickers microhardness and creep of InBi single crystals

      V P Bhatt C F Desai

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      Variation of Vickers microhardness of InBi single crystals with temperature has been studied. Loading time dependence of the microhardness at different temperatures has been used for the creep study in the temperature range 30° – 85°C. The activation energy for creep has been evaluated and the results are discussed.

    • Fracture toughness of cast aluminium alloys

      S Ranganatha Malur N Srinivasan

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      An investigation was carried out to evaluate the fracture toughness of cast aluminium alloys of different microstructural complexity, brought about by alloy constitution and cooling rate of castings. In all cases the three-point bend specimens, which had a thickness of 15 mm, did not provide valid plane — strain stress intensity factor values. The fracture susceptibility at a given stress level reckoned in terms of the conditional plane strain stress intensity factor (KQ) was found to be lowest in aluminium-4.5% copper alloy castings and the susceptibility increased with increase in microstructural complexity. Casting cooling rate in these castings is likely to affect the damage potential of a given defect at yield stress to a greater extent than the fracture susceptibility at a given stress.

    • Dislocation loops in tungstenite (WS2) crystals

      MK Agarwal K Nagi Reddy JV Patel

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      TEM studies of tungstenite crystals grown by sublimation method have been investigated. Dislocation loops observed during such studies have been reported. It has been shown by different methods that these loops have a vacancy character.

    • A simple technique for interference microtopography

      P B V Prasad I V K Bhagavan Raju

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      A simple and inexpensive technique for obtaining the interference microtopographs of crystal surfaces is reported. The method consists of forming a low angle air wedge by placing a thin glass sheet (cover slide) on the surface of the sample. Interferograms are taken under reflected sodium light.

    • Structural, magnetic and electrical study of MgCoMnO4

      S G Joshi D K Kulkarni P V Khandekar

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      A new compound MgCoMnO4 has been synthesised by the oxide method. It crystallizes in a tetragonal spinel structure witha=8.30 A andc=8.46 A. The observed crystal symmetry is associated with the existence of Mn+3 on theB sites. The compound isn type semi-conductor with activation energy ΔE=0.33 eV. The electrical properties show that it can be regarded as a properly substituted MgMn2O4 by Co+3 ions. It is paramagnetic withCM=5.75 and ϑa =−160°K. All these results show the ionic configuration of the compound as Mg+2 [Co+3 Mn+3] O4.

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