S. A. Patil

Conductivity, dielectric behaviour and magnetoelectric effect in copper ferrite-barium titanate composites

Composites of CuFe2O4 and BaTiO3 were prepared using a conventional ceramic double sintering process. The presence of both phases was confirmed by X-ray diffraction. The variations of resistivity and thermo emf with temperature in these samples were studied. All the composites showed n-type behaviour. The variation of dielectric constant (έ′) in the frequency range 100 Hz to 1 MHz and with temperature at constant frequency were studied. The conduction phenomenon was explained on the basis of a small polaron-hopping model. Also confirmation of this phenomenon was made with the help of a.c. conductivity measurements. The static value of the magnetoelectric conversion factor, i.e. d.c. (ME)H was studied as a function of intensity of the magnetic field. The maximum value of ME coefficient was observed for 75% ferroelectric phase composite.

Electrical Conduction and Magnetoelectric Effect in CuFe1.8Cr0.2O4–Ba0.8Pb0.2TiO3 Composites

Magnetoelectric composites of CuFe1.8Cr0.2O4– Ba0.8Pb0.2TiO3 were prepared using high temperature solid-state reaction technique. X-ray structural analysis of these composites confirms the presence of both the phases in the composite. Detailed studies of dielectric properties (ε′, tan δ and σac) as a function of frequency (100 Hz to 1 MHz) and temperature (30°C to 250°C) show that these compounds exhibit diffuse ferroelectric phase transitions. Results of ac conductivity, dc resistivity and thermoelectric power measurements show that conduction occurs by hopping of charge carriers. The magnetoelectric effect has been studied as a function of intensity of magnetic field. The electrical polarisation was induced in piezoelectric (Ba0.8Pb0.2TiO3) phase as result of strain induced in the ferrite (CuFe1.8Cr0.2O4) phase by the applied magnetic field. The Jahn-Teller distortion caused in the ferrite lattice by Jahn-Teller ions like Cu2+ and Cr3+ is also responsible for the elastic coupling of strain to the Ba0.8Pb0.2TiO3 phase.

D.C. conductivity and dielectric behavior of Ti4+ substituted Mg-Zn ferrites

Abstract The variation of d.c. resistivity (ρ) and activation energy (ΔE) with Ti4+ concentration show similar behaviour. The gradual change of ρ for low Ti4+ concentration is attributed to the occupation of the A sites by Ti4+ ions and additional Fe3+ ions becoming available to the B sites. The linear increase of resistivity for higher Ti4+ concentration is attributed to an overall decrease Fe3+ ions on Ti4+ substitution. Dispersion of the dielectric constant is related to the Verwey conduction mechanism. Peaks have been observed in the variation of loss tangent (tan δ) with Ti4+ concentration. These peaks shift to the low frequency side on increasing the content of Ti4+. The jump frequencies are found to be in the range 70–120 kHz. All the samples exhibit space charge polarization due to an inhomogeneous dielectric structure. It is concluded that the addition of Ti4+ obstructs the flow of space charge.

Dielectric behaviour and a.c. conductivity in Cu x Fe3−x O4 ferrite

The dielectric properties (dielectric constant and loss) for the system CuxFe3−xO4 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.

Structural, dielectric and transport properties of Pb(Mno.5Wo.5)O3

Polycrystalline Pb(Mn0.5W0.5)O3, a ferroelectric oxide having perovskite structure, was prepared by high temperature solid state reaction technique. Preliminary X-ray diffraction analysis confirms single phase formation with the lattice parametersa = 7.2501 Å,b = 8.1276 Å andc = 12.0232 Å. Room temperature dielectric constant (ε′) and loss tangent (tan δ) were scanned with respect to frequency in the range 100 Hz-1 MHz. Detailed study of dielectric constant and electrical conductivity reveals a phase change around 400 K, which is quite different from those in the other materials of the same type. Further, the seebeck coefficient (α) is temperature independent. The conduction is interpreted as due to small polaron hopping.

Role of sintering on magneto-electric effect in CuFe1.8Cr0.2O4-Ba0.8Pb0.2Ti0.8Zr0.2O3 composite ceramics

Magnetoelectric composites containing CuFe1.8Cr0.2O4–Ba0.8Pb0.2Ti0.8Zr0.2O3 phases have been prepared by sintering them at different firing temperatures. The particle size for either phase of the composite was found to increase, whereas porosity decreases with increase in sintering temperature. This is due to the increase in the grain size with increase in sintering temperature. Resistivity of the composite decreases with increase in either sintering temperature or with increase in CuFe1.8Cr0.2O4 content. The variation of dielectric constant (e′) with temperature reflects DPT type behaviour. The peak value of dielectric constant (e′max) for a composite decreased with increase in its sintering temperature. The maximum value of the magnetoelectric conversion factor (dE/dH)max equal to 182.7 μV/(cm*Oe) is obtained for 70% Ba0.8Pb0.2Ti0.8Zr0.2O3–30% CuFe1.8Cr0.2O4 composite when sintered at 1000°C.

Electrical properties of Si4+ substituted copper ferrite

The electrical resistivity, ϱ, and Seebeck coefficient, α, for the system Cu1+xSixFe2−2xO4 (where x = 0.05, 0.1, 0.15, 0.2 and 0.3) have been studied as a function of temperature. Temperature variation of the resistivity exhibits two breaks. Each break is associated with a change in activation energy. The conduction process at low temperature is governed by the reaction CuA1++ CuA2+→CuA2++ CuA1+. However, at higher temperature, it is due to intersite cation exchange and reoxidation such as CuA2++ FeB3+→ CuB2++ FeA3+. Measurement of the Seebeck coefficient, α, from room temperature to 800 K reveals n-type conduction for the sample with x= 0.05, while the measurements for other samples show p-type conduction for lower temperatures and n-type conduction at higher temperatures. The activation energies in the paramagnetic region are found to be less than those in the ferrimagnetic region.

Studies on structural, dielectric and magnetoelectric properties in CuFe1.8Cr0.2O4– Pb(Mg1/3V2/3)O3 composites

Abstract CuFe 1.8 Cr 0.2 O 4 –Pb(Mg 1/3 V 2/3 )O 3 composites were prepared using a conventional ceramic double sintering process. The presence of both phases in the composites was confirmed by X-ray diffraction studies. Variation of dielectric constant (ϵ′) with frequency in the range 100 Hz–1 MHz and also with temperature for four different frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz) was studied. The nature of the peaks indicate DPT type behaviour. The static value of magnetoelectric conversion factor, i.e., DC(ME) H has been studied as a function of intensity of the magnetic field. The maximum value of DC(ME) H was found to be 164.33 μV/cm/Oe for 70% ferrite phase.

X-ray and bulk magnetic studies on Li0.5ZnxTixFe2.5−2xO4

Abstract Lattice parameter ‘a’ in the system Li 0.5 (ZnTi) x Fe 2.5−2x O 4 increases monotonically with x, which is attributed to ionic volume differences of the cations involved. The grain size dm increases with the increase of (Zn 2+ Ti 4+ ) concentration to x = 0.3 while for x > 0.3 the grain size shows a decrease with increase of x. The initial permeability first increases gradually and then rapidly with temperature, μi = 0 at T c and its value drops sharply near T c , suggesting single phase territe formation. The addition of Ti 4+ enhances μi values while T c values are lowered. The increase of ui with x is due to a decrease of K 1 The decrease of T c with x is attributed to weakening of A-B interactions due to overall reduction of Fe 3+ ions. From 1 KHz onwards μi is frequency independent while all the samples show large dispersion on the low frequency side. Variation of n B with x reveals that for x B increases with increase of x while for x > 0.3, n B decreases with increase of x. Normalised susceptibility studies show that all the samples contain M.D. particles.

Conduction in Mn substituted Ni-Zn ferrites

The d.c. electrical resistivity ‘ρ’ and thermoelectric power ‘α’ are studied as a function of temperature for Mn substituted ferrites with general formula Zn0·3Ni0·7+xMnxFe2−2xO4. At lower Mn concentrations, the increase in d.c. resistivity is attributed to the hindering of Verwey mechanism Fe2+ ⇌ Fe3+ due to stable bonds of Mn3+ + Fe2+ pair. The decrease in resistivity at higher Mn concentrations (i.e. whenx > 0·15) is attributed to the formation of Mn3+ cluster and Ni2+ ⇌ Ni3+. The activation energy values show one to one correspondence with resistivity values. The compositional variation of thermoelectric power showsn-type behaviour for the samples withx < 0·2 whereasp-type behaviour for the samples withx ⩾ 0·2. Thep −n transition is attributed to the formation of Ni3+, Fe2+ + vacancies which act asp-type carriers. The temperature dependences ofα, ρ, and mobility clearly confirm the conduction mechanism to be due to polaron hopping.