Neetu Ahlawat

Phase transformation, dielectric and magnetic properties of Nb doped Bi0.8Sr0.2FeO3 multiferroics

Bi0.8Sr0.2Fe1−xNbxO3 (x = 0.0, 0.05, and 0.10) multiferroics were prepared by solid state reaction method. X-ray diffraction and Rietveld analysis show that crystal structure is rhombohedral for x = 0.0, 0.05 samples and triclinic for x = 0.10 sample. These samples showed dispersion in dielectric constant (έ) and dielectric loss (tan δ) values at lower frequencies. For x = 0.05 sample, both έ and tan δ are lower than for Bi0.8Sr0.2FeO3 sample indicating its high resistivity. For x = 0.10 sample, the value of έ is enhanced which may be due to formation of stronger dipoles in triclinic structure. Temperature dependence of frequency exponent “s” of power law suggests that correlated barrier hopping (CBH) model is applicable at lower temperatures and quantum mechanical tunneling model is appropriate at higher temperatures for describing the conduction mechanism in x = 0.0 and x = 0.05 samples; while in x = 0.10 sample, CBH model is appropriate in studied temperature range. Significant enhancement observed in magnetization for x = 0.10 sample is due to the structural phase transition from rhombohedral to triclinic caused by Nb substitution. For this sample, values of remnant magnetization (Mr) and coercive field (Hc) are 0.155 emu/g and 2.695 kOe, respectively.Bi0.8Sr0.2Fe1−xNbxO3 (x = 0.0, 0.05, and 0.10) multiferroics were prepared by solid state reaction method. X-ray diffraction and Rietveld analysis show that crystal structure is rhombohedral for x = 0.0, 0.05 samples and triclinic for x = 0.10 sample. These samples showed dispersion in dielectric constant (έ) and dielectric loss (tan δ) values at lower frequencies. For x = 0.05 sample, both έ and tan δ are lower than for Bi0.8Sr0.2FeO3 sample indicating its high resistivity. For x = 0.10 sample, the value of έ is enhanced which may be due to formation of stronger dipoles in triclinic structure. Temperature dependence of frequency exponent “s” of power law suggests that correlated barrier hopping (CBH) model is applicable at lower temperatures and quantum mechanical tunneling model is appropriate at higher temperatures for describing the conduction mechanism in x = 0.0 and x = 0.05 samples; while in x = 0.10 sample, CBH model is appropriate in studied temperature range. Significant enhancement observed in ...

Structural transformation and improved dielectric and magnetic properties in Ti-substituted Bi0.8La0.2FeO3 multiferroics

Ti-substituted BiLaFeO3 ceramics having compositions Bi0.8La0.2Fe1?xTixO3 (x?=?0.0, 0.05, 0.1, 0.15) were synthesized by the conventional solid-state reaction method. Powder x-ray diffraction investigations performed at room temperature show that the crystal structure is rhombohedral for x?=?0.0, 0.05; tetragonal for x?=?0.15; and a phase boundary occurs at x?=?0.1. In the Rietveld refinement good agreement between the observed and calculated pattern was observed. Dielectric response of these samples was analysed in the frequency range 1?kHz?5?MHz at different temperatures. A decrease in the values of real (??) and imaginary (??) parts of dielectric constant with Ti substitution indicates reduced conductivity and hence enhanced resistivity in doped samples. Stability of dielectric constant and conductivity with temperature is considerably improved with Ti substitution. Magnetic measurements were carried out at room temperature up to a field of 20?kOe. Magnetic properties of Bi0.8La0.2FeO3 ceramics are considerably improved on Ti substitution along with a significant opening in the room temperature M?H hysteresis loop. Higher values of remanent magnetization (Mr) 0.1373 and 0.1487?emu?g?1; coercivity (Hc) 4.856 and 5.904?kOe are observed for samples with x?=?0.1 and 0.15, respectively. This is due to the structural phase transition from rhombohedral to tetragonal.

Improved dielectric and magnetic properties of Ti modified BiCaFeO3 multiferroic ceramics

Ti substituted BiCaFeO3 ceramics having compositions Bi0.8Ca0.2Fe1−xTixO3 (x = 0.0, 0.1, 0.2) were synthesized by the conventional solid state reaction method. Powder X-ray diffraction investigations performed at room temperature show that all samples possess a rhombohedrally distorted perovskite structure described by the space group R3c. Rietveld refinement presented a good agreement between the observed and calculated patterns. Dielectric response of these samples was analyzed in the frequency range 1 kHz–5 MHz at different temperatures. Dispersion in dielectric constant (έ) and dielectric loss factor (tanδ) values decreases with Ti substitution. έ increases and tanδ decreases significantly by Ti substitution. Magnetic measurements were carried out at room temperature up to a field of 20 kOe. Magnetic properties of Bi0.8Ca0.2FeO3 ceramic are greatly improved on Ti substitution along with a significant opening in the room temperature M-H hysteresis loop. The values of remnant magnetization (Mr) 0.08 and...

Structure refinement and dielectric relaxation of M-type Ba, Sr, Ba-Sr, and Ba-Pb hexaferrites

M-type hexaferrites with compositions BaFe12O19 (BFO), SrFe12O19 (SFO), Ba0.5Sr0.5Fe12O19 (BSFO), and Ba0.5Pb0.5Fe12O19 (BPFO) were synthesized by commercial solid state reaction method. The Rietveld refinement of x-ray powder diffraction revealed a single hexagonal phase with space group P63/mmc for BFO, SFO, and BSFO samples, whereas BPFO sample contains hematite (α-Fe2O3) phase with space group R3c along with the M-type main phase. All the samples show dispersion in dielectric constant (ɛ′) and dielectric loss (tan δ) values with frequency. The values of ɛ′ and tan δ increase with increase in temperature due to increase in the number of charge carriers and their mobilities, which are thermally activated. The reciprocal temperature dependence of conductivity (σac) and the most probable relaxation time (τM″) satisfies the Arrhenius relation. A perfect overlapping of the normalized plots of modulus isotherms on a single “super curve” for all the studied temperatures reveals a temperature independence of d...

Effect of Zr substitution on phase transformation and dielectric properties of Ba0.9Ca0.1TiO3 ceramics

Ba0.9Ca0.1Ti1−xZrxO3 (x = 0.05, 0.07 and 0.10; BCTZ5, BCTZ7, BCTZ10) lead free ceramics were prepared by solid state reaction. The phase transitional behaviour, composition, and temperature dependent electrical properties and composition dependent ferroelectric properties were investigated. XRD analysis at room temperature and Rietveld refinement revealed a structural transformation from tetragonal to rhombohedral with enhancement of Zr content in the BCT matrix. Study of impedance spectra of these ceramics confirmed a heterogeneous electrical microstructure where the conduction and relaxation mechanisms originated from grain boundaries and grains. The ceramics depicted non Debye type of relaxation. Dielectric properties illustrated a decrease in Curie temperature and a diffused phase transition behavior with increase in Zr content. The conducting species changed from V′o to V′′o on ferroelectric phase transition in grain interiors. Saturated hysteresis loops confirmed the ferroelectric nature of the cera...

Structural and dielectric properties of Ca0.95 Nd0.05Cu3Ti3.95Zr0.05O12 ceramic

ABSTRACT The unique dielectric properties of CaCu3Ti4O12 (CCTO) are a promising feature for capacitor applications. Polycrystalline Ca0.95Nd0.05Cu3Ti3.95Zr0.05O12 ceramic was synthesized via conventional solid state method. XRD and Rietveld studies confirmed that crystal structure is cubic with space group Im3. Microstructural study by scanning electron microscopy (SEM) suggests that the compound has some abnormal grains embedded with small grains depict inhomogeneous microstructure. The dielectric properties were analyzed in frequency range from 100 Hz to 5 MHz at different temperatures. A giant dielectric constant (∼19,426) with minimal loss tangent (∼0.067 at 1 KHz) at room temperature is achieved in studied composition.

Structural investigation and giant dielectric response of CaCu 3 Ti 4 O 12 ceramic by Nd/Zr co-doping for energy storage applications

High performance dielectric materials are highly required for practical application for energy storage technologies. In this work, high-k pristine and modified calcium copper titanate having nominal formula Ca0.95Nd0.05Cu3Ti4−xZrxO12 (x = 0.01, 0.03 & 0.10) were synthesized and characterized for structural and dielectric properties. Single phase formation of the synthesized compositions was confirmed by X-ray diffraction patterns and further analysed using Rietveld refinement technique. Phase purity of the synthesized ceramics was further confirmed by Energy-dispersive X-ray Spectroscopy (EDX) analysis. SEM images demonstrated that grain size of the modified CCTO ceramics was controlled by Zr4+ ions due to solute drag effect. Impedance spectroscopy was employed to understand the grain, grain boundaries and electrode contribution to the dielectric response. Nyquist plots were fitted with a 2R-CPE model which confirms the non-ideality of the system. Substitution of specific concentration of Nd and Zr improved the dielectric properties of high dielectric permittivity (ε′ ~ 16,902) and minimal tanδ (≤ 0.10) over a wide frequency range. The giant ε′ of the investigated system was attributed to internal barrier layer capacitance (IBLC) effect and reduced tanδ accredited to enhanced grain boundaries resistance due to substitution of Zr4+ ions at Ti4+ site.

Effect of microwave-assisted sintering on dielectric properties of CaCu3Ti4O12 ceramic

In this present work, CaCu3Ti4O12 (CCTO) was synthesized by conventional solid-state reaction technique. The synthesis process was carried out in two phases; by conventional process (calcination and sintering at 1080°C for 10 hours) and phase II involves the micro assisted pre sintering of conventionally calcined CCTO for very short soaking time of 30 min at 1080°C in a microwave furnace followed by sintering at 1080°C for 10 hours in conventional furnace. X-ray diffraction (XRD) patterns confirmed the formation of single phase ceramic. Dielectric properties were studied over the frequency range from 50Hz -5MHz at temperatures (273K-343K). It was observed that pre- microwave sintering enhance the dielectric constant values from 10900 to 11893 and respectively reduces the dielectric loss values from 0.49 to 0.34 at room temperature(1 KHz). CCTO ceramics which are found desirable for many technological applications. The effect is more pronounced at low frequencies of applied electric field.

The effect of temperature on ferroelectric properties of CaCu3Ti4O12 ceramic

CaCu3Ti4O12 (CCTO) ceramic was synthesized by conventional solid-state reaction technique and sintered at 1353K for 10 hours. The dielectric properties of CCTO were analyzed in 1Hz-5 MHz frequency range, from room temperature to 413K. The ferroelectric properties of CCTO were analyzed at various frequencies viz. 50 Hz, 100 Hz and 200 Hz at temperatures (298K to 413K). Result of these investigation points that with increasing temperature the values of coercive field (Ec) and remnant polarization (Pr) decrease while maximum polarization (Pmax) increases non-linearly. P-E hysteresis loop of CCTO goes to slimed and a ferroelectric to Para-electric phase transition is observed at 403K.

Rietveld Refinement and DC Conductivity of Na0.5K0.5NbO3 Ceramics

Potassium Sodium Niobate, Na0.5K0.5NbO3 is a promising base material for lead free piezoceramics. The polycrystalline sample Na0.5K0.5NbO3 was synthesized using solid state reaction method. The crystal structure and phase purity was studied by XRD and analysed using Rietveld refinement method. Good agreement was observed between the observed and calculated patterns in Rietveld refinement. The refinement inferred orthorhombic crystal structure with Amm2 space group. The impedance spectroscopy of the sample was performed in frequency range 10 Hz to 7 MHz in temperature range 573K to 703K. The activation energy was obtained to be 0.67eV from the reciprocal temperature variation of dc conductivity which follows the Arrhenius law.