D. D. Pandya

Size-controlled electrical properties of sol–gel-grown nanostructured Gd0.95Ca0.05MnO3

In this communication, we report the results of the studies on electrical properties of cost-effective modified sol–gel-grown nanostructured Gd0.95Ca0.05MnO3 (GCMO) manganites sintered at different temperatures. Structural investigations, carried out using X-ray diffraction measurements, reveal the single-phasic nature of GCMO samples having orthorhombic unit cell structure. Frequency-dependent variation in AC conductivity (σAC) has been discussed on the basis of correlated barrier hopping (CBH) mechanism for the GCMO samples sintered at lower temperatures. Sintering temperature-induced transition from CBH mechanism to Maxwell–Wagner relaxation processes has been discussed in detail. Size-induced modifications in the impedance response of the samples have been understood, in detail, using size effects and Cole–Cole plots.Graphical Abstract

Temperature-dependent I–V and C–V characteristics of chemically-grown Y0.95Ca0.05MnO3/Si thin films

In this communication, we report the results of the studies on temperature-dependent current—voltage (I–V) and capacitance—voltage (C–V) characteristics of chemical solution deposition-grown Y0.95Ca0.05MnO3/Si films and annealing temperature-induced modified interface dependence on device characteristics. X-ray diffraction results reveal the single phasic nature of films having polycrystalline growth on single crystalline (100) Si substrate. The magnetic nature of the films is confirmed from magnetic force microscopy studies. I–V and C–V characteristics show a strong dependence on the temperature and nature of the film—substrate interface, which has been understood on the basis of the annealing effect involved. Various models and theories have been used to understand the mechanism responsible for the transport across the film—substrate interface. A large rectifying ratio of ~1.2 × 104 has been obtained across the interface annealed at a lower temperature, which becomes almost double in the film annealed at a higher temperature. A large electroresistance of ~600% has been achieved for the interface annealed at a lower temperature. The temperature dependence of C–V behavior recorded across the interfaces of the films is discussed in detail on the basis of free and trapped charge carrier density and interface modifications.

Structure – Transport Correlations in Mono-Valent Na+ Doped La1-xNaxMnO3 Manganites

We report the results of the structural, transport and magnetotransport studies on mono-valent doped La1-xNaxMnO3 (LNMO) (x = 0.05, 0.1 and 0.15) manganites. XRD measurement and Rietveld refinement on LNMO samples shows that, all the samples crystallize in distorted rhombohedral structure without any additional impurity peaks. The d.c. four probe resistivity measurements show that, the metal-insulator transition temperature (TP) exhibited by the Na doped manganites increases and resistivity decreases with increasing x. This behavior has been explained on the basis of size disorder effect, tolerance factor variation and structural modifications due to large size mono-valent Na-doping. In the metallic region, the resistivity data have been fitted to the zener double exchange (ZDE) polynomial law for all the three samples. Magnetoresistance (MR) studies show a decrease in low temperature (5K) MR while increase in room temperature MR with increase in Na-content in the LNMO manganites.

Structure-property correlations in monovalent mixed oxide La1−xKxMnO3(0.0≤x≤0.3)manganites

Substitution of monovalent K+ at La3+ in solid state reaction synthesized La1−xKxMnO3(0.0≤x≤0.3) manganites results in metallic behavior. Increase in K+ content (x ≤ 0.15) enhances the FM interactions through ZDE mechanism while for higher x > 0.15, structural disorder and AFM interactions between Mn4+ ions become prominent.

Temperature dependent dielectric behavior of sol–gel grown Y0.95Ca0.05MnO3/Si junction

We have successfully fabricated divalent doped Y0.95Ca0.05MnO3 film on (100) single crystalline n-type Si substrate by spin coating assisted chemical solution deposition technique. The X–ray diffraction (XRD) pattern of thin film depicts that the film has (h00) directional growth on substrate. Thin film possesses –1.4% compressive strain at the interface level and thin film thickness is found to be ∼ 78nm. Dielectric property of film has been studied by Agilent LCR meter from 100Hz to 2MHz applied field frequency at temperatures 150 to 300K. Real dielectric permittivity decreases and imaginary dielectric permittivity increases with increasing applied frequency. Furthermore, at low temperatures, higher dielectric is observed in all the frequency range studied and it decreases with increasing temperature due to thermal excitation induced increased charge carrier movements across the film lattice. The relaxation mechanism of Y0.95Ca0.05MnO3 film has been understood through cole–cole plots.

Investigations of magnetoelectric behavior in BiFe0.95Co0.05O3 nanoparticles

Nanophasic BiFe0.95Co0.05O3 (BFCO) particles were synthesized using low cost, easy, simple, environment friendly and low temperature acetate precursor based modified sol–gel method. Influence of particle size and magnetic field on the structural, dielectric, impedance and a.c. conductivity of BFCO is investigated. X-ray diffraction (XRD) measurement has been performed to understand the structural modifications in the samples upon increasing the sintering temperature. Crystallite size (CS) increases from 33.62nm to 39.56nm due to agglomeration effect between the smaller crystallites. Effect of sintering temperature on the dielectric, impedance and conductivity has been studied and understood in the context of the creation of crystallite (particle) size and oxygen vacancies created due to high temperature sintering process. Magnetic field induced modifications in all these electrical properties [magnetoelectric (ME) effects] for the presently studied BFCO samples have been discussed on the basis of magnetos...

Effect of sintering temperature on the structural and electrical properties of Zn0.95Cr0.05O

In this communication, we report the results of the studies on the sintering temperature dependent structural properties and dielectric behavior of 5% Cr doped Zn0.95Cr0.05O samples synthesized by cost effective sol-gel technique. Crystallographic orientations, crystallinity and crystallite size (CS) have been understood by performing X-ray diffraction (XRD) measurement at room temperature. Values of CS have been further verified by carrying out Williamson – Hall (W-H) plot analysis and the difference between the CS from XRD and W-H analyses has been discussed. Dielectric behavior has been studied and its dependence on the sintering temperature has been understood in the light of crystallite size, crystal boundary density and oxygen vacancies induced possible conductivity in the samples.

Investigations on structural disorder-induced modifications in the transport behaviour of rare-earth manganites

The results of the studies on structural disorder-induced modifications in the transport behaviour of La0.5Pr0.2Ca0.3−xBaxMnO3 (LPCBMO) (0.05 ≤ x ≤ 0.30) manganites were reported. Structural studies using X-ray diffraction (XRD) measurements confirmed the single phasic nature of all the samples without any detectable impurities. The A-site size disorder (σA2

I-V and C-V characteristics of Y0.95Ca0.05MnO3/Si film

{ {\sigma }}_{\mathrm{A}}^{\mathrm{2}}

Structure-property correlations in La1-xNaxMnO3 manganites

) increased from 3.81 × 10−5 (x = 0.05) to 14.9 × 10−5 (x = 0.30). With the increase in structural disorder in LPCBMO system, the transport improved for the range: 0.15 ≤ x ≤ 0.30, which can be ascribed to the enhancement in one electron bandwidth which dominates over the structural disorder effect, while for lower values of x, strong competition existed between size disorder and one electron bandwidth. Below 50 K, all ρ–T plots showed resistivity minimum behaviour, which modified with disorder. This behaviour was discussed in detail on the basis of electron–electron interaction having the form: ρ=[1/(σ0+BT1/2)]+ρnTn