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In the present work, oxygen vacancy induced dielectric relaxations were studied for Lanthanum substituted Bi4-xLaxTi3O12 (x = 0.0, 0.3, 0.7, 1.0) ceramics. X-ray diffraction patterns reveal the formation of single phase orthorhombic structure in all the samples. The partial substitutions of lanthanum ions were found to significantly influence the g...
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... if we plot the M 00 data in scaled coordinates, i.e., M 00 /M 00 max versus log (f/ f max ) , where f max is the maximum frequency, we can derive the shape of relaxation time spectrum at different temper- atures. Figure 7a, b shows the normalized master curve for sample BIT7 and BIT10. The master modulus curve is characterized by: observation of peak with a cross over from long range to short range mobility of ions with rise in temperature and greater FWHM than the width of a typical Debye peak of 1.14 decades [35]. ...
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... Consequently, it became necessary to reduce its bandgap maintaining its ferroelectric response for visible light PV applications [11]. Physical properties of the Bi 4 Ti 3 O 12 compound can be controlled either by single doping at Bi or Ti site [13][14][15][16][17][18] or by co-doping on both sites simultaneously [19][20][21][22]. H Zhang et al [23], based on band structure theory, reported that Cr 3+ ions doping on the Ti 4+ site of BiT does not affect the position of the valance band edge, but new energy levels were formed within the bandgap resulting in photocatalytic activity in the energy range of the visible light. ...
Reducing bandgap energy in ferroelectric materials has become an important commitment to improve the performance of the photovoltaic solar cell. This study reports the effect of the transition metals (TM) Co and Fe ions co-doping on the structure and bandgap of Neodymium-modified Bi4Ti3O12 based oxide (BNdT). Phase structure was confirmed by XRD and structural refinement confirms that all samples are crystallized with an orthorhombic crystal structure that belongs to the B2cb space group. Optical properties were measured by a UV-vis spectrometer. The oxygen vacancies presence and the possible valence states of Fe and Co were confirmed by ESR study. The incorporation of Co/Fe ions significantly modified the bandgap, promoting a red-shift, and lower energies absorption, as a consequence of the changes in tilting angle, bond lengths, octahedral distortions, and oxygen vacancies formation, still maintaining a ferroelectric spontaneous polarization. To our knowledge it a new approach to link quantitively the octahedra distortion to the bandgap decreasing for Aurivillius compounds, and the present work will provide researchers with an available way of manipulating the bandgap tuning on the ferroelectric oxide's materials.
... It can also be perceived that films prepared after longer irradiation shows a frequency stretching in response profile with phase-reversal identical to the conventionally prepared samples. The full width at half maxima estimated from the impedance loss spectra (Z" vs log f) is greater than 1.144 decades (of the ideal Debye response), suggesting a departure from Debye-type relaxation [75]. The plots of Z"(f) in lower frequencies at different temperatures from 30 • C to 65 • C substantiate the presence of interfacial polarization effect. ...
Near room temperature LPG sensing ability of polycrystalline nanoparticulate SnO2 thin films prepared by pyrolysis of microwave irradiated (MwI) precursor is investigated without any post annealing process. This technique facilitates to produce homogeneous nano-structured thin films in just 15 min. The phase composition, morphology, and microstructure of the films obtained by pyrolysis of different duration MwI precursors are examined by XRD, FT-IR, TEM and HRTEM. The gas sensing properties of the films display a significant advancement in lowering LPG and CO2 sensing temperature in addition to sensitivity in comparison with the films from unirradiated precursor. The LPG sensors have shown considerable response down from 50 ppm at a lower operating temperature of 50 °C and for CO2 from ∼150 °C, along with high selectivity to NH3 and NO2. The 1 min irradiated films exhibit an excellent LPG response of −98.4 % in 500 ppm with a resistance ratio Ra/Rg of 78, whereas for 3 min irradiated, the CO2 response is +77.9 % in 500 ppm of gas. The photoluminescence and dielectric properties are investigated to elucidate the factors responsible for the enhancement in response of the microwave processed films. From the results of the impedance investigation, the role of interface states promoted by defects in microstructure on the gas sensing of SnO2 films is discussed.
... Hence, it is reasonable to associate the present relaxation peak with the hooping process of oxygen vacancies in BGFCT sample. It was reported that La substitution can improve the activation energy E a of oxygen vacancies in Bi 4 Ti 3 O 12 ceramics, suggesting decreased concentration of oxygen vacancies in Ladoped Bi 4 Ti 3 O 12 [45]. Besides, oxygen-annealed stoichiometric and La-doped Bi 4 Ti 3 O 12 samples show higher activation energy E a , which is attributed to the reduction in the concentration of oxygen vacancies. ...
The magnetic, dielectric, and magnetodielectric properties of bi-layered perovskite Bi4.25Gd0.75Fe0.5Co0.5Ti3O15 (BGFCT) ceramics were investigated. Weak ferromagnetism at room temperature with a remnant magnetization Mr of 0.26 emu/g was found in the BGFCT specimens, and the ferromagnetic transition was determined at ~383 K. The change in valence state for magnetic ions has been confirmed by the XPS measurement, which would introduce ferromagnetism via double-exchange interaction. The Dzyaloshinsky–Moriya interaction was also proposed to explain weak ferromagnetism. The ferroelectric phase transition around 1072 K has been verified by the temperature-dependent dielectric measurement and differential scanning calorimetry. The standard positive-up–negative-down tests indicated the intrinsic ferroelectricity of BGFCT, and an obvious MD effect was observed in the temperature range from 190 to 280 K. The dielectric loss of the BGFCT exhibits one dielectric relaxation with activation energy Ea ~ 0.49 eV, which is related to the hooping of oxygen vacancies.
... It's associated to ionic conductivity, which is caused by the loss of oxygen during high-temperature sintering. Thus, this defect plays an important role in the conductivity of LST, which causes the dielectric loss increase [19]. Between 600 and about 680 °C , tanδ slightly decreases with increasing temperature, which is due to the decreasing of the relaxation time [16,20]. ...
La₁-xSr
x
TiO3+δ (LST) has been studied in many fields, especially in the field of microelectronics due to its excellent electrical performance. Our previous theoretical simulated work has suggested that LST has good dielectric properties, but there are rare reports about this, especially experimental reports. In this paper, LST was prepared using a solid-state reaction method. The X-rays diffraction (XRD), scanning electron microscope (SEM), broadband dielectric spectroscopy, impedance spectroscopy and photoconductive measurement were used to characterize the sample. The results show that the values of dielectric parameters (the relative dielectric constant εr and dielectric loss tanδ), dependent on temperature, are stable under 350 °C and the value of the relative dielectric constant and dielectric loss are about 52-88 and 6.5 × 10-3, respectively. Its value of conductivity increases with rise in temperature, which suggests its negative temperature coefficient of the resistance. In addition, the band gap of LST is about 3.39 eV, so it belongs to a kind of wide-band-gap semiconductor materials. All these indicate that LST has anti-interference ability and good dielectric properties. It could have potential applications as an electronic material.
The solid-state reaction route created the lead-free dielectric material CaBiLaNbVO9 at a high temperature. The polycrystalline compound belongs to a monoclinic crystal structure having dimensions a = 10.6738 Å, b = 10.4488 Å, c = 7.1793 Å, and V = 798.04 ų. The grain size is calculated to be 1.1029 µm. The doping of La³⁺ at the Bi-site and divalent cation Ca²⁺ substituted at site-A and Nb⁵⁺, V⁵⁺ in the site-B of ABO3 has considerably modified the structural, dielectric, and electrical conduction mechanism. The study of ac conductivity (frequency-temperature characteristics) shows CBH (correlated barrier hopping) and NSPT (non-overlapping small polaron tunneling) conduction mechanisms. Non-Debye type relaxation has been observed using impedance analysis. The modulus and impedance study have been used to confirm the short-range order of charge carriers. The average transmittance of the compound is about 82–84%, and absorption is in the range of 0.1–1.0% in the visible area applicable for transparent conductive oxide. The energy band gap is 2.73 eV. The analysis of the resistive and capacitive properties indicates the material is an electronic component for the creation of devices.
Graphical Abstract
In this manuscript, we report room‐temperature structural, microstructural, optical, dielectric, and magnetic properties of CuO and Cu0.995La0.005O ceramics, synthesized by solid‐state reaction method. La doping in CuO leads to the evolution of compact and dense microstructure with reduced porosity. Due to noticeable differences in the ionic radii of Cu²⁺ (0.73 Ǻ) and La³⁺ (1.03 Ǻ), La doping creates vacancy defects which induces considerable strain in the CuO lattice resulting in a reduction in the lattice parameters and cell volume. However, both ceramics process similar monoclinic structure with C2/c space group. Detailed characterization using X‐ray photoelectron spectroscopy, Raman, and Fourier‐transform infrared spectroscopy confirmed the incorporation of the La³⁺ in CuO lattice. Interestingly, La doping enhances the dielectric constant and results in a reduced leakage current. The onset of large dielectric constant is attributed to dense microstructure and strain/distortion in CuO lattice after La doping. Additionally, the bandgap of Cu0.995La0.005O ceramics decreases which is attributed to increased vacancy defect concentration that creates intermediate dopant energy level within bandgap of CuO matrix. Furthermore, improvement in magnetic and dielectric properties is also discussed and correlated with the grain size in La‐doped CuO.
0.7BiFeO3-0.3BaTiO3+1mol% MnO2(0.7BFO-0.3BTO) ceramics were synthesized by conventional solid-state powder method under different calcination temperatures (Tcal) between 770 and 830 °C. The phase structure, microstructure, and ferroelectric and piezoelectric properties changed greatly depending on the applied Tcal. Benefitting from the formation of low defect levels and large grain size and an appropriate morphotropic phase boundary (MPB) with the rhombohedral-to-pseudocubic phase ratio = 49.1 : 50.9, BFO-BTO ceramics calcined at 785 °C showed the best ferroelectric, piezoelectric, and insulating properties (Pr = 23.1 μC/cm², EC = 25.8 kV/cm, d33 = 167.8 pC/N, kp = 0.342%). Above Tcal = 800 °C, however, the ferroelectric and piezoelectric properties deteriorated because volatilization of Bi and reduction of Fe caused a poor insulating property and high degree of chemical inhomogeneity. Moreover, the ceramics calcined at 785 °C showed a high Curie temperature (TC) of 509.2 °C and excellent thermal aging resistance of d33 up to 450 °C, demonstrating great potential for use in high-temperature applications.
Piezoelectric photocatalysis has been considered as a fascinating solution to promote the effective separation of photogenerated carriers for the efficient removal of organic pollutants. Herein, we report that micro-morphology plays a decisive role in determining piezo potential enhanced photocatalytic activities. The high deformation capacity of Bi3.25La0.75Ti3O12 (BLT) nanowires leads to superior piezo-photocatalytic activity compared to BLT nanosheets and BLT nanospheres for efficient removal of refractory 2,4-Dichlorophenol (2,4-DCP) and tetracycline (TC). One-dimensional materials exhibit extremely high elasticity due to their greatly reduced size, allowing for a large degree of mechanical deformation. Under light and ultrasonic, the removal rates of 2,4-DCP and TC by BLT nanowires reached 93.04% and 96.30% after 60 min and 12 min, respectively, which were 2.97 and 2.96 times higher than those by light irradiation only. Furthermore, the ultrasonic power and frequency are important factors to optimize the piezoelectric catalytic and piezo-photocatalytic performance. Modulating the morphology of the material can regulate the piezoelectric effect of the material to suit different practical needs. Moreover, it is simpler to obtain efficient piezoelectric effects through morphology optimization than to design and develop new materials for a wider range of applications.
Piezoelectric thermal stability characteristics of (K,Na,Li)NbO3 ceramics were investigated with a particular focus on the role of oxygen vacancy defects, by excluding the lattice distortion or microstructural effects with the help of a low level of Mn doping (less than 1.0 mol%). Benefiting from the reduction of intrinsic oxygen vacancy defects, controlled Mn doping (0.25 mol%) could achieve excellent ferroelectric/piezoelectric activity and superior thermal aging resistance. Beyond this doping level, however, the defect dipoles combined with extrinsic oxygen vacancies, although advantageous to the hardening effect, deteriorated the piezoelectric thermal stability and aging resistance including room-temperature properties. The thermal dissociation and migration of oxygen-vacancy-associated defect dipoles were considered mainly responsible for negating the ability to restore the initial poled domain state with defect-dipole-induced polarization. Results demonstrated the importance of keeping the intrinsic and extrinsic oxygen vacancy levels as low as possible for lead-free (K,Na)NbO3 systems with more thermally stable domain structure.
