A.R. James

Structural properties and impedance spectroscopy of excimer laser ablated Zr substituted BaTiO3 thin films

BaZr0.15Ti0.85O3 thin films were deposited on Pt-coated Si substrates using the pulsed excimer laser ablation technique. X-ray diffraction and atomic force microscope techniques were used to study the structural characteristics of the films. Films with good crystalline quality, with an average grain size of 0.5 µm were obtained, under various oxygen background pressures. Ferroelectric hysteresis loops recorded on the films deposited at 26.66 Pa oxygen pressure showed the best properties. To gain a further understanding of the electrical properties of these films, impedance spectroscopy was used and data acquired at several different temperatures. AC conductivity plots showed the presence of space charge conduction at low frequencies; however, at high frequencies, all the curves merged and expectedly showed an almost dc conduction behaviour. The activation energy obtained from ac conductivity data may be attributed to oxygen vacancy motion.

Structural and electrical properties of nanocrystalline PLZT ceramics synthesized via mechanochemical processing

Nanocrystalline powders of La-modified lead zirconate titanate (PLZT: 7/60/40) solid solution have been synthesized via mechanochemical processing. No excess PbO was used in the starting composition. Scanning and transmission electron microscopy revealed the formation of powders on the nano-scale. Sintering the powders resulted in dense compacts, at reduced sintering temperatures. Well-saturated ferroelectric hysteresis loops with a Pr on the order of ~48??C?cm?2 and coercive fields of ~7?kV?cm?1 were recorded on the samples. Strain levels up to > 0.25% with limited hysteresis (<0.05% in the low field region) indicate the tremendous potential of these ceramics for high-performance actuators, especially in cases where a high degree of positioning accuracy is required.

DEGREE OF DIFFUSED PHASE TRANSITION AND NON-DEBYE DIELECTRIC RELAXATION IN Ba(NdxTi1-2xNbx)O3 CERAMICS

Dielectric measurements were made over the temperature range 80–300 K at different frequencies (10 kHz, 50 kHz, 100 kHz, 500 kHz and 1 MHz). The degree of relaxor behavior and diffuseness of phase transition were correlated to the cationic disorder at lattice site B. Non-Debye dielectric behavior was observed in the present samples and a modified Arrhenius relation proposed by Chen et al. was found to best describe the frequency dependent dielectric maxima temperature.

Diffuse phase transition in mechanically activated (Pb1−xLax)(Zr0.60Ti0.40)O3 electro-ceramics

In this paper, the dielectric properties of (Pb1−xLax)(Zr0.60Ti0.40)O3 (referred to from now on as PLZT x/60/40) ceramics were investigated for the optimization of La substitution at the A-site of PZT ceramics. The PLZT x/60/40 ceramic powders were synthesized by mechanical activation and compaction of these fine scale nano powders was done using cold isostatic pressing. The present study suggests that lanthanum substitution affects the nature of the ferroelectric phase transition of PZT showing a deviation from normal to the diffuse type phase transition (DPT). The parameters of this DPT, such as the degree of deviation from Curie–Weiss law (ΔTm), diffuseness empirical parameters γ and ΔTdiff were calculated for different compositions of PLZT ceramics at 1 kHz. The large value of γ (1 < γ < 2) and ΔTdiff confirms the deviation from normal phase transition and the high degree of disorderliness in the material. It is also found that the Curie temperature Tc and maximum dielectric constant εmax both decrease with increasing La3+ content. The maximum value of dielectric constant for the PLZT 8/60/40 ceramics was found to be ~1975.

Structural and dielectric properties of phosphorous-doped PLZT ceramics

In the present work we have reported the unique effects of P2O5-doped PLZT ceramics with composition (Pb0.92La0.08)(Zr0.65Ti0.35)O3 +x wt% of P2O5 (wherex = 1, 3 and 5) prepared chemically by co-precipitation method. X-ray diffraction studies suggest that the prepared compound was very fine (10–25 nm), homogeneous and of rhombohedral symmetry. The apparent density of samples decreased with the P5+ additions. Studies of dielectric constant and dielectric loss as a function of frequency (10–1000 kHz) and temperature suggest that the compound undergoes diffuse type of phase transition without any sign of relaxor behaviour. With increasingx, dielectric constant was found to decrease appreciably, whereas Curie temperature (TC) was found to increase

Improved ferroelectric, piezoelectric and electrostrictive properties of dense BaTiO3 ceramic

The ferroelectric, piezoelectric and electrostrictive properties of BaTiO3 (BT) dense ceramic synthesized by solid-state reaction were investigated. X-ray diffraction study confirmed tetragonal crystal structure having c/a ~1.0144. The dense microstructure was evidenced from morphological studies with an average grain size ~7.8 µm. Temperature dependent dielectric measurement showed the maximum values of dielectric constant, er = 5617 at Curie temperature, Tc = 125 °C. The saturation and remnant polarization, Psat. = 24.13 µC/cm2 and Pr =10.42 µC/cm2 achieved respectively for the first time with lower coercive field of Ec=2.047 kV/cm. The polarization current density-electric field measurement exhibits the peaking characteristics, confirms the saturation state of polarization for BT. The strain-electric field measurements revealed the “sprout” shape nature instead of typical “butterfly loop”. This shows the excellent converse piezoelectric response with remnant strain ~ 0.212% and converse piezoelectric c...

Dielectric and ferroelectric studies on lead free piezoelectric KNN ceramics

(K0.5Na0.5)NbO3 (KNN) ceramics are synthesized by solid state reaction method. The processing parameters such as calcination and sintering temperatures were optimized to get the stoichiometric KNN ceramics at lower processing temperatures. The effect of calination temperature on structural, microstructural and dielectric properties was investigated. The KNN ceramics calcined at 700°C and sintered at 950°C exhibited the best structural, microstructural, ferroelectric and dielectric properties. The dielectric studies revealed that that both the dielectric constant and tanδ of KNN ceramics as function of temperature exhibited two sharp phase transitions indicating orthorhombic to tetragonal and ferroelectric tetragonal to paraelectric cubic phases. The prepared ceramics exhibited fine ferroelectric properties of remnant polarization and coercive field are 8.8μC/cm2 and 11.01KV/cm, respectively.

Enhanced piezo response in mechanically activated and microwave sintered PLZT 8/60/40 ceramics

In this present study, the issue of lead volatility in (Pb_0.92La_0.08)(Zr_0.60Ti_0.40)O₃ (PLZT 8/60/40) ceramics is addressed by the combinatorial approach of high energy ball milling and microwave sintering. The XRD patterns were used for the phase analysis. Higher relative density (~99%) and uniform grain distribution (~1.2 μm) were found for PLZT 8/60/40 ceramics, which was microwave sintered at 1150°C. The dielectric constant for the unpoled PLZT ceramics was found to be ~2100 at 1 kHz frequency with very low dielectric loss (~0.03). The saturated P-E and S-E ferroelectric hysteresis loops as well as the domain switching current peak in I-E loop confirms the ferroelectric nature of PLZT ceramics. The high remnant polarization ~33 μC/cm², low coercive field ~10 kV/cm and high strain ~0.26%, was shown by the ceramics which was microwave sintered at 1150°C. The piezoelectric charge (d₃₃) was found to be ~575 pC/N.