Structural and electrical properties of four folded layered BaBi2Sb2Ti4O15 compound

Impedance and electric modulus analysis of Sm-modified Pb(Zr 0.55Ti 0.45) 1− x/4 O 3 ceramics

In this work, Zn co-doped tungsten bronze having nominal formula Ba5CaTi1.94Zn0.06Nb8O30 has been synthesized and systematically studied for structure, dielectric and electrical properties. The formation of the phase of tetragonal tungsten bronze with space group P4bm and the occurrence of oxygen vacancies were verified by the Rietveld refinement using X-ray diffraction data. Scanning electron microscopy (SEM) of Ba5CaTi1.94Zn0.06Nb8O30 ceramic shows high densification, low porosity, and homogeneous distribution of grains of different sizes over the total surface. The sample shows a dielectric anomaly of ferroelectric paraelectric type at 262 °C, and has non-relaxor type of diffuse phase transition. The electrical property (complex impedance Z*, complex permittivity ε*, complex modulus M*) of Ba5CaTi1.94Zn0.06Nb8O30 ceramic has been investigated by non-destructive complex impedance spectroscopy (CIS) as a function of frequency at different temperatures. Grains and grain boundaries conduction is detected from a complex impedance spectrum by fitting the Nyquist plot with an appropriate electrical circuit. The Nyquist plot indicates the negative temperature coefficient of resistance (NTCR) character of Ba5CaTi1.94Zn0.06Nb8O30 ceramic. The variation of AC conductivity as a function of frequency reveals that the compound has an Arrhenius-type behavior of electrical conductivity. The DC electrical conductivities of grains and grain boundaries have been studied. The presence of non-Debye relaxations was verified by a complex modulus analysis.

Structural and electrical characteristics of double perovskite: Nd2CoMnO6

Ba0.5Bi0.5Ti0.5Fe0.5Mn0.1O3, a Fe-based Mn-modified BFO-BT ceramic, is processed by solid-state reaction route, calcined at 950 °C temperature. Formation of single-phase orthorhombic structure is observed from room temperature XRD analysis. Dielectric behavior is investigated over a broad range of temperature (30 °C–500 °C) and frequency (0.1 kHz–10 MHz). Broadening of transition temperature is noticed at 460 °C, where the material undergoes a change from ferro- to paraelectric state. From dielectric plots the effect of Mn on capacitive behavior of the material is studied. The conductivity study exhibits negative temperature coefficient of resistance (NTCR) behavior showing semiconducting behavior of the material.

A conventional solid-state method was used to prepare Pb(Fe1/3Ti1/3W1/3)O3 single perovskite material. The sample sintered at 900?C was studied by XRD and after Rietveld refinement the orthorhombic structure with Pbam space group was confirmed. The FTIR frequency bands corresponding to Pb-O, Ti-O, O-lattice, W- O-W and Fe-O stretching vibrations together with the XRD data also confirmed that Fe2+ and W6+ ions are incorporated in the structure and most probably substituted Ti4+ ions at the B site of the perovskite ABO3 structure. The average grain size of the perovskite ceramics, estimated from SEM micrograph, was 1 to 2 ?m. Variation of dielectric properties and AC conductivity with frequency and temperature revealed that the material had semiconducting nature and negative temperature coefficient of resistance (NTCR). The Nyquist plots were modelled with an equivalent circuit consisted of parallel capacitance, resistance and constant phase element corresponding to the grains (bulk) and grain boundaries. It was observed that grain resistance (Rb) of the sample decreases with the rise of temperature, which supports the NTCR behaviour. The semi-circular arcs of the Nyquist and Cole-Cole plots confirm the semiconducting nature of the sample.

Preparation and characterization of LiFe 1/2Ni 1/2VO 4

Magnesium aluminum silicate (MgO-Al2O3-SiO2, MAS) glass-ceramic was prepared via sintering route. X-ray diffraction (XRD) analysis indicates the formation of multiphase compound with magnesium silicate fluoride and cordierite as major phases. Dielectric studies of the compound shows a strong frequency dispersion of permittivity in the low frequency region followed by a nearly frequency-independent behavior in the high frequency region. The presence of alkali ions (K+) in MAS glass-ceramic results in higher dielectric constant and higher losses. Dielectric loss (tanδ) seems to be reduced at higher frequencies after reaching the instrumental saturation at 1 kHz. Electrical properties of the material have been studied using a complex impedance spectroscopy (CIS) technique in a wide temperature (30–500 °C) and frequency (100 Hz-5 MHz) ranges. The complex impedance plots reveal the contribution of bulk as well as grain boundary effects in it. The bulk resistance, evaluated from complex impedance spectrum, has been observed to decrease with the rise in temperature, showing a typical negative temperature coefficient of resistance (NTCR) behavior. The smaller activation energy (Ea) of the compound within moderate temperature range suggests the presence of ions (K+ and F−) and singly ionized oxygen vacancies in the conduction process. The nature of variation of the electrical conductivity, and the values of activation energy of different temperature regions, suggest that the conduction process is of mixed type.

Influence of ionic radius of rare-earths on the structural and electrical properties of Ba5RTi3Nb7O30 (R=rare-earth) ferroelectric ceramics

Structural, vibrational, dielectric and electrical properties of (Na0.5Bi0.5)(Zr0.025Ti0.975)O3 ceramic synthesized by the solid-state reaction technique have been carried out. The X-ray diffraction analysis was indicated as a pure perovskite phase in the rhombohedral structure. The modes of rhombohedral vibrations were appeared in the experimental Raman spectrum at room temperature. The dielectric and electrical properties of the material were investigated by impedance spectroscopy analysis for a broad range of temperatures (50–560 °C) and frequency domain of 102−106 Hz. The dielectric measurement exhibit two phase transitions: a ferro-antiferroelectric transition followed by an antiferro-paraelectric transition at higher temperatures. Complex impedance analysis was carried out in order to distinct the contribution of the grains and the grain boundaries to the total electrical conduction. The Nyquist plot was proved to be a non-Debye relaxation mechanism. The combined spectroscopic plots of the imaginary part of electric impedance and modulus confirmed the non-Debye type behavior. The frequency dependent ac conductivity obeys the double power law behavior and shows three types of conduction process. The significant decrease of dc conductivity spectrum followed the Arrhenius relationship. The values of calculated activation energy of the compound implied that the electrical conduction is mostly due the high oxygen mobility.

Effect of Fe supplantation on structural and dielectric properties of La2CoMnO6

BST ceramics with doping of 1, 3, and 5 wt.% ZnBO were prepared by the conventional mixed oxide method and sintered at 1100°. X-ray diffraction analyses were carried out to verify the structural properties. 1, 3, and 5 wt.% ZnBO doped BST ceramics were crystallized with weak tetragonal structure at 1100°C. The grain growth behavior and shapes were investigated by scanning electron microscopy images. The electrical properties of 1, 3, and 5 wt.% ZnBO doped BST ceramics were investigated by impedance spectroscopy at the different temperatures (350, 375, and 400°C). Impedance spectroscopy data presented in Nyquist plot show the existence of both grain and grain boundary effects in all specimens. 1, 3, and 5 wt.% ZnBO doped BST ceramics showed negative temperature coefficient of resistance (NTCR). Also, the capacitances and resistances of grains and grain boundaries for 1, 3, and 5 wt.% doped BST ceramics were simulated through equivalent circuit with the parallelly connected capacitors and resistors. The capacitance and resistance were decreased when temperature and ZnBO dopants were increased.

In the present work, the effect of partial substitution of barium by calcium in Ba5NdTi3Nb7O30 has been investigated. The samples were synthesized by solid state reaction method and studied for their structural, dielectric, conductivity and ferroelectric properties. The X-ray diffractograms confirm the formation of single phase orthorhombic tungsten-bronze structure. Detailed dielectric properties of the compounds as a function of frequency and temperature show that the compounds undergo non-relaxor type ferroelectric-paraelectric phase transition of diffuse nature. An increase in Curie temperature (Tc ) from 100°C to 140°C is observed on the substitution of calcium. The Polarization–Electric field (P-E) studies show that the remanent polarization (2Pr ) increases on the substitution of calcium in Ba5NdTi3Nb7O30. The temperature dependence of dc-conductivity shows that the conductivity increases with increase in temperature revealing the negative temperature coefficient of resistance (NTCR) behaviour of the compounds.

Broad-temperature-span and improved piezoelectric/dielectric properties in potassium sodium niobate-based ceramics through diffusion phase transition

Ammonium dihydrogen phosphate (ADP) is an important nonlinear optical (NLO) material used for electro-optical applications. The aromatic side chain contained dopant like L-phenylalanine causes defect in ADP. The pure and L-phenylalanine doped ADP crystals are grown using slow solvent evaporation technique at room temperature. The Powder XRD spectra suggest tetragonal crystal system and slit shifting of peak. The FT-Raman shows strong absorption peak at 922 cm−1 due to v1 group symmetry of P - OH for all grown crystals without shifting indicating the single phase nature of all the crystals. The photoluminescence study suggests the presence of defects in doped crystals compared to the pure one due to increase of Stokes shift and vibrational energy relaxation phenomena. The dielectric constant and dielectric loss have shown the usual behavior with respect to frequency and temperature. The calculated electro-optic coefficient is found to be in accordance with dielectric constant. The protonic conduction is prevailing for electric transport, and from Jonscher’s plot, the correlation barrier hopping (CBH) is confirmed. The Nyquist plot and modulus spectra of pure ADP show the presence of grain and grain boundary while the same plots for L-phenylalanine doped ADP show the presence of grain only. The stretch exponent exhibits non-Debye-type relaxation.

Investigation of structural, electrical and dielectric properties of sol-gel prepared La0.67-xEuxBa0.33Mn0.85Fe0.15O3 (x=0.0, 0.1) manganites