Ferroelectric materials and their applications

With the purpose of fabricating ceramics where ferroelectric and magnetic order coexist, ceramics of Pb(Fe1∕2Nb1∕2)O3 have been prepared using the traditional ceramic method following three different routes. The first is a direct via starting from oxide reagents and the other two use different kinds of FeNbO4 precursors with either monoclinic or orthorhombic structures. Crystallographic and surface morphological studies were carried out by the powder x-ray diffraction and scanning microscopy techniques. The presence of Fe2+, detrimental to the ferroelectric and magnetic performance, was evaluated by x-ray photoelectron spectroscopy. The samples showed no structural differences, uniformly distributed grains, a ferro-paraelectric transition temperature at 110°C and a normal diffuse phase transition (nonrelaxor behavior). Differences in the degree of diffuseness, densities and grain size were observed depending on the kind of precursor. Measurements of dc and ac electrical resistivity, dielectric constant an...

Frequency-temperature response of ferroelectromagnetic Pb(Fe1∕2Nb1∕2)O3 ceramics obtained by different precursors. Part I. Structural and thermo-electrical characterization

Science Foundation Ireland ((SFI FORME Strategic Research Cluster Award number 07/SRC/I1172), (SFI Starting Investigator Research Grant (09/SIRG/I1621)), (SFI 09/SIRG/I1615)); European Commission (COST Action MP0904 (Single and multiphase ferroics and multiferroics with restricted geometries (SIMUFER)).

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Magnetic Field-Induced Ferroelectric Switching in Multiferroic Aurivillius Phase Thin Films at Room Temperature

The dielectric behavior of ferroelectromagnetic Pb(Fe1∕2Nb1∕2)O3 ceramics obtained using the traditional ceramic method employing three different precursors was investigated by impedance spectroscopy in the temperature range of 200–300°C. This study was carried out by means of the simultaneous analysis of the complex impedance Z, electric modulus M, and admittance Y functions from the measurements in the frequency range of 20Hz–1MHz. In correspondence to a previous structural, morphological, and temperature response study, appropriate microstructural and equivalent circuit models were established. Based on the brick layer model, three series of interconnected electrically distinct regions are considered: a conductive grain boundary layer, a capacitive grain boundary surface layer, and a resistive-ferroelectric bulk layer. Two conduction mechanisms were identified: a dielectric relaxation process due to localized conduction associated with the presence of oxygen vacancies and the nonlocalized conduction...

Frequency-temperature response of ferroelectromagnetic Pb(Fe1∕2Nb1∕2)O3 ceramics obtained by different precursors. Part II. Impedance spectroscopy characterization

Dielectric relaxation behavior of AxCo1−xFe2O4 (A = Zn, Mg) mixed ferrites

The compound, LaBi5Fe2Ti3O18, is a five-layered material belonging to the family of bismuth layered structure ferroelectromagnetics. D.c. and a.c. conductivity measurements were performed on the samples. Dielectric measurements were also performed on these samples. Combined impedance and modulus plots were used as tools to analyse the sample behaviour as a function of frequency. Cole-Cole plots showed non-Debye relaxation.

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Synthesis, impedance and dielectric properties of LaBi5Fe2Ti3O18

We performed a systematic analysis of the structure, ferroelectric and photocatalytic activities of Sm and V co-doped Bi4Ti3O12 (SBVT) ceramics. The formation of 3-layered Aurivillius structure and chemically induced strain of SBVT were analyzed by SEM and HRTEM studies. From the results of structural refinements, temperature dependent XRD and Raman spectra we found that SBVT has a distorted orthorhombic structure and transforms to tetragonal in the temperature range of 475–600 °C. Raman modes of Bi sites experience the phase transition earlier compared to torsional bending modes of BO6 octahedra. From the results of polarization and piezoelectric strain measurements, we found that SBVT exhibits superior ferroelectric characteristics as well as improved S33 (0.02 × 10−3) compared to other rare-earth doped Bi4Ti3O12 materials reported in the literature. SBVT exhibited fatigue endurance up to 108 switching cycles. Such a behavior is attributed to the structural distortions due to the smaller ionic radius of Sm3+ and reduced oxygen vacancies. Local piezoresponse measurements demonstrated imprint characteristics of ferroelectric domains. Furthermore, we assessed the photocatalytic (PC) activity of SBVT – for the first time – in the gas–solid phase, monitoring the degradation of nitrogen oxides (i.e. NO + NO2). Results demonstrated that SBVT was photocatalytically active in the solar spectrum, being able to degrade NOx at ppb level concentration, and exhibited a very stable PC activity (five consecutive PC runs), proving itself suitable for reuse.

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Effect of samarium and vanadium co-doping on structure, ferroelectric and photocatalytic properties of bismuth titanate

Magnetic and magnetoelectric measurements on rare-earth-substituted five-layered Bi6Fe2Ti3O18 compound

Co x
 Cd1−x
 C2O44H2O crystals grown by gel technique are characterized for dielectric properties by optical absorption measurements. Loss curve shows a relaxation peak at 500 KHz corresponding to a relaxation time of 0·3 µs. Cole-Cole diagrams give exponent of universal power law to be equal to 0·22. Optical absorption shows peaks due to Co+2 ion and water of hydration. An attempt is made to understand the results.

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Dielectric properties of cobalt doped cadmium oxalate crystals

Impedance spectroscopic measurements were carried out on lead based ferroelectric ceramics, namely PZT, PLZT and PMN-PT, in the frequency range of 0.1 Hz–1 MHz. Spectroscopic plots showed broad peaks, and are found to shift towards higher frequency side. Apart from this, both Z″ and M″ spectroscopic peaks are found to coincide almost in the same frequency region. This indicates approximated-Debye behavior. Frequency dependent conductivity plots show two slopes at lower and higher frequency regions. Low frequency relaxations are found to be non-exponential. Bulk relaxation vs. temperature plots are found to obey Arhenius linear fit. The relaxation at lower frequency and higher are attributed to Kohlrausch-Williams-Watt (KWW) type and migration of slow oxygen and lead vacancies. The results are corroborated to the conduction barrier hopping mechanism and new Eyraud's conductivity model.

N. V. Prasad

Papers

Synthesis, impedance and dielectric properties of LaBi5Fe2Ti3O18

Effect of samarium and vanadium co-doping on structure, ferroelectric and photocatalytic properties of bismuth titanate

Magnetic and magnetoelectric measurements on rare-earth-substituted five-layered Bi6Fe2Ti3O18 compound

Dielectric properties of cobalt doped cadmium oxalate crystals

Impedance Spectroscopic Studies on Lead Based Perovskite Materials