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The dielectric properties (dielectric constant and loss) for the system Cu x Fe 3-x O 4 with x = 1⋅ ⋅0, 0⋅ ⋅8, 0⋅ ⋅6, 0⋅ ⋅4 and 0⋅ ⋅2, were studied in the temperature range 300 ∼ ∼ 800 K and also in the frequency range 1 kHz ∼ ∼ 1 MHz. A.c. conductivity was derived from dielectric constant and loss tangent data. The conduction in this system is interpreted as due to small polaron hopping. The dielectric relaxation was observed for the compositions with tetragonal structure whereas normal behaviour was observed for cubic structure.

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a The isostructural family of three dodecanuclear chiral M4Cu8 (M = Dy, Y) complexes has been synthesized by adopting a mixed-ligand strategy, wherein one of the constituent linker Pyroglutamic acid, a recognized biomolecule has been credibly functioning as the chiral precursor imparting the chirality to the aforementioned complex. The highly symmetric new-fangled M4Cu8 cordination-core, comprising of four square-symmetricallly coordinated Dy/Y-vertex sharing M2Cu2 cubane units has been synthesized as an unprecedented discrete coordination complex, which has been analysed by magnetic measuremnets.

The dc electrical resistivity (q) and thermoelectric power (α) are studied as functions of temperature for Mn‐substituted ferrites with general formula Cd0.3Ni0.7 + xMnxFe2−2xO4. At lower Mn concentrations (i.e., x < 0.15) the increase in dc resistivity is attributed to hindering the Verwey mechanism between Fe2+ ⇄ Fe3+. This is due to the stable bond formation of Mn3+ + Fe2+ at octahedral sites. The decrease in resistivity at higher concentration (i.e., x > 0.15) is attributed to the formation of Mn3+ clusters which lowers the concentration of Mn3+ + Fe2+ bonds. The compositional variation of thermo‐e.m.f. shows n‐type behaviour for the samples with x less than 0.15, whereas p‐type behaviour for the samples with x > 0.15. The n‐p transition is attributed to the formation of Ni3+ and Fe2+ + vacancies which act as p‐type carriers. The thermo‐e.m.f. remains constant for all the samples at the measured temperatures. The temperature dependences of α, Q, and mobility clearly confirm the conduction mechanism to be due to polaron hopping. The compositional variations of dielectric constant show two regions, one for x ≦ 0.15 in which the dielectric behaviour is due to Fe3+ ions and the other for x > 0.15, where the nature of the dielectric is complex. The complex dielectric structure might have its origin in the different valence states of Mn, inhomogeneities within the ferrite grain, and oxygen stoichiometry.

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Electrical resistivity of Cd Ni "in Fe 0 ferrites has been . 0 3 0 .2*X(. X 2-7x. 't . • • measured in the temperature range fr'orn iuu3 k 10 tuuo 1<: . 1 hree distmction

The electrical resistivity and Seebeck coefficient for Ni-Cd ferrites have been studied as a function of temperature. The lattice constant of the phases have been evaluated from X-ray powder data. The thermoelectric power measurements indicate that the samples are n-type semiconductors and the conduction mechanism is interpreted on the basis of localized model of polarons.