Multiferroic bismuth ferrite-based materials for multifunctional applications: Ceramic bulks, thin films and nanostructures

Author(s): Ahn, KH; Wu, XW; Liu, K; Chien, CL | Abstract: The effect of Fe doping (l20%) on the Mn site in the ferromagnetic ((Formula presented)) and the antiferromagnetic ((Formula presented)) phases of (Formula presented) has been studied. The same ionic radii of (Formula presented) and (Formula presented) cause no structure change in either series, yet conduction and ferromagnetism have been consistently suppressed by Fe doping. Colossal magnetoresistance has been shifted to lower temperatures, and in some cases enhanced by Fe doping. Doping with Fe bypasses the usually dominant lattice effects, but depopulates the hopping electrons and thus weakens the double exchange. © 1996 The American Physical Society.

Magnetic properties and colossal magnetoresistance of LaÑCaÖMnO3 materials doped with Fe

Investigation of bismuth borate glass system modified with barium for structural and gamma-ray shielding properties.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/EXP.20210005

Nanozyme for tumor therapy: Surface modification matters

Electrical characterizations of Nb2O5 doped 0.65BiFeO3–0.35BaTiO3 (0.65BF–0.35BT) ceramic were carried out over broad temperature and frequency ranges through dielectric spectroscopy, impedance spectroscopy, and ac conductivity measurements. The dielectric constant and loss tangent are drastically reduced with introducing Nb2O5 into the 0.65BF–0.35BT system. Two dielectric anomalies are detected in the temperature regions of 100 °C ≤ T ≤ 280 °C and 350 °C ≤ T ≤ 480 °C, and the Curie temperature (TC) was confirmed in higher temperature region. A dielectric relaxation with large dielectric constants was detected near the TC. This dielectric relaxation becomes even stronger with the gradual increase in the Nb2O5 content. Impedance spectroscopy results clearly show the contributions of grains and grain boundaries in the frequency range of 100 Hz ≤ f ≤ 1 MHz, and the relaxation processes for grains and grain boundaries are non-Debye-type. The grain boundaries are more resistive than that of the grains, revealing the inhomogeneity in samples. The experimental results are well fitted based on a Maxwell-Wagner (MW) interfacial polarization model below 100 kHz, and the MW interfacial polarization effect becomes more and more obvious with the increase in the Nb2O5 content. The increase in dielectric constant is possibly related to space charge polarization, which is caused by charges accumulated at the interface between the grain and grain boundaries. Frequency dependence of the ac conductivity confirms the MW interfacial polarization effect below 100 kHz.

Dielectric relaxation and Maxwell-Wagner interface polarization in Nb2O5 doped 0.65BiFeO3–0.35BaTiO3 ceramics

Structural and optical properties of barium titanate modified bismuth borate glasses

The presence of superlattice reflections and detailed analyses of the powder neutron and x-ray diffraction data reveal that La rich (BF$_{0.50}$-LF$_{0.50}$)$_{0.50}$-(PT)$_{0.50}$ (BF-LF-PT) has ferroelectric rhombohedral crystal structure with space group \textit{$R3c$} at ambient conditions. The temperature dependence of lattice parameters, tilt angle, calculated polarization $(P_{s})$, volume, and integrated intensity of superlattice and magnetic reflections show an anomaly around 170 K. Impedance spectroscopy, dielectric and ac conductivity measurements were performed in temperature range $473K \leq T \leq 573K$ to probe the origin of large remnant polarization and frequency dependent broad transitions with large dielectric constant near $T_c^{FE}$. Results of impedance spectroscopy measurements clearly show contributions of both grain and grain boundaries throughout the frequency range ($10^{3}$ Hz$\leq f\leq 10^{7} $ Hz). It could be concluded that the grain boundaries are more resistive and capacitive as compared to the grains, resulting in inhomogeneities in the sample causing broad frequency dependent dielectric anomalies. Enhancement in dielectric constant and remnant polarization values are possibly due to space charge polarization caused by piling of charges at the interface of grains and grain boundaries. The imaginary parts of dielectric constant ($\epsilon^{\prime\prime}$) Vs frequency data were fitted using Maxwell-Wagner model at $T_c^{FE}(\sim 523$K) and model fits very well with the data up to $10^{5}$ Hz. Magnetodielectric measurements prove that the sample starts exhibiting magnetoelectric coupling at $\sim 170$ K, which is also validated by neutron diffraction data.

Origin of Large Dielectric Constant with Large Remnant Polarization and Evidence of Magnetoelectric Coupling in Multiferroic La modified BiFeO3-PbTiO3 Solid Solution

The glass samples with composition (70B2O3-29Li2O-1Dy2O3)-xBT; x = 0, 10 and 20 weight percent, have been prepared by conventional melt quench technique. The dielectric measurements as a function of temperature have been carried out on these samples in the frequency range 1 Hz-10 MHz. The dielectric relaxation characteristics of these samples have been studied by analyzing dielectric spectroscopy, dielectric loss, electric modulus formulation and electrical conductivity spectroscopy. It is found that the dielectric permittivity of the samples increases with an increase in the temperature and BT content. The frequency dependent ac conductivity has been analyzed using Jonscher’s universal power law whereas non exponential KWW function has been invoked to fit the experimental data of the imaginary part of the electric modulus. The values of the activation energy determined from the electric modulus and that from dc conductivity have been found to be quite close to each other suggesting that the same type of charge barriers are involved in the relaxation and the conduction mechanisms. The stretched exponent (β) and the power exponent (n) have been found to be temperature and composition dependent. The decrease in n with an increase in temperature further suggested that the ac conduction mechanism of the studied samples follows the correlated barrier hopping (CBH) model.

Temperature dependent electrical transport characteristics of BaTiO3 modified lithium borate glasses

The presence of superlattice reflections and detailed analysis of the powder neutron and x-ray diffraction data reveals that La rich BLF-PT (BFO0.50–LF0.50)0.50–(PT)0.50 has a ferroelectric rhombohedral crystal structure with space group R3c at ambient condition. Impedance spectroscopy, dielectric spectroscopy is subset of impedance spectroscopy and ac conductivity measurements were performed in the temperature range 483 K ≤ T ≤ 573 K to probe the origin of large remnant polarization and frequency dependent broad transitions with large dielectric constant near TcFE. Results of impedance spectroscopy measurements clearly show contributions of both grain and grain boundaries throughout the frequency range (1 kHz ≤ f ≤ 10 MHz). It could be concluded that the grain boundaries are more resistive and capacitive as compared to the grains, resulting in inhomogeneity in the sample and cause broad frequency dependent dielectric transitions. The Maxwell-Wagner model fits very well up to ∼105 Hz. Enhancement in diele...

Origin of large dielectric constant in La modified BiFeO3-PbTiO3 multiferroic

Magnetoelectric coupling coefficient (α) values of 0.88mV∕cm∕Oe at 200Oe and magnetocapacitive effects are reported in solid-solution BF–LF–PT with large La substitution (50:50 in BF). Enhancement of magnetic, dielectric, and ferroelectric properties is also observed. The solid solution shows relaxor behavior with large permittivity values (∼30000), large remnant polarization (∼61μC∕cm2), and symmetric but nonsaturating M-H loop with Mr∼0.25emu∕g.

Anupinder Singh

Papers

Structural and optical properties of barium titanate modified bismuth borate glasses

Origin of Large Dielectric Constant with Large Remnant Polarization and Evidence of Magnetoelectric Coupling in Multiferroic La modified BiFeO3-PbTiO3 Solid Solution

Temperature dependent electrical transport characteristics of BaTiO3 modified lithium borate glasses

Origin of large dielectric constant in La modified BiFeO3-PbTiO3 multiferroic

Enhanced magnetoelectric coefficient (α) in the modified BiFeO3–PbTiO3 system with large La substitution