Narrow Results

Spontaneous polarization and its strain effects of bismuth titanate (BiT) with B2cb and B1a1 space groups are studied by first-principles density functional theory (DFT) calculation. B1a1 was proved to be the most stable phase structure and the spontaneous polarization is in good agreement with the experimental value. Similar variations of the principal polarization component (P_a) are obtained for B2cb and B1a1 structured BiT by applying b-uniaxial, c-uniaxial, ab-biaxial and bc-biaxial strains. It is found that the P_a is enhanced about 18.5% (20.8%) with ab-biaxial tensile strain of 2.4% for B2cb(B1a1) structure. Polarization along the c-axis (P_c) for the B1a1 structure is improved by 59.1% when bc-biaxial tensile strain reaches 2.4%.

In this study, electrical parameters of the Al/Bi₄Ti₃O${}_{12}$/p-Si metal-ferroelectric-semiconductor (MFS) structure and their temperature dependence were investigated using current–voltage (I–V) data measured between 120 K and 300 K. Semi-logarithmic I–V plots of the structure revealed that fabricated structure presents two-diode behavior that leads to two sets of ideality factor, reverse saturation current and zero-bias barrier height (BH) values. Obtained results of these parameters suggest that current conduction mechanism (CCM) deviates strongly from thermionic emission theory particularly at low temperatures. High values of interface states and nkT/q−kT/q plot supported the idea of deviation from thermionic emission. In addition, $ln$(I)−$ln$(V) plots suggested that CCM varies from one bias region to another and depends on temperature as well. Series resistance values were calculated using Ohm’s law and Cheungs’ functions, and they decreased drastically with increasing temperature.

The Aurivillius-type compounds with generic formula Sr_xBi_4-xNb_xTi_3-xO₁₂ (with x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) have been synthesized to investigate the effect of Sr and Nb substitution on the bismuth titanate, by a conventional solid state technique. The phase formation of the compound was confirmed through XRD. The dielectric measurements were made at different constant frequencies of 10 kHz, 50 kHz, 100 kHz, 500 kHz and 1 MHz over a wide temperature range. The samples showed a transition from normal ferroelectric behavior to relaxor dielectric behavior with an increasing value of "x".

In this work, fabrication and investigation of substituing high-valence W⁶⁺ for Ti⁴⁺ ion on B-site of La³⁺-doped Bi₄Ti₃O₁₂ or BLT structure to form Bi_3.25La_0.75(Ti_1-xW_x)₃O₁₂ or BLTW (when x = 0, 0.01, 0.03, 0.05 0.07, 0.09 and 0.10) ceramics were carried out. X-ray diffraction patterns of BLTW ceramics indicated orthorhombic structure with lattice distortion, especially with higher concentration of WO₃ dopant. An increase in WO₃ doping content reduced not only length and thickness of grain, but also density of the ceramics. Electrical conductivity was found to decrease, while dielectric constant increased with W⁶⁺ doping. Ferroelectric properties were found to be improved with increasing WO₃ content and were optimized at x = 0.05.

Aiming at the influence of substitution on ferroelectric behaviors, Nd and Mg/Mn cosubstituted bismuth titanate films, Bi_3.15Nd_0.85Ti_2.97Mg_0.03O₁₂ (BNTMg) and Bi_3.15Nd_0.85Ti_2.95Mn_0.05O₁₂ (BNTMn), have been prepared on Pt/Ti/SiO₂/Si(100) substrates at 700°C by a chemical solution deposition technique, respectively. A series of comparisons including structures, surface morphologies, and ferroelectric properties of the as-prepared films were carried out by X-ray diffraction, scanning electron microscope, and a Radiant Technologies Precision Workstation for ferroelectric test system. It was found that the films possess preferred the (117) and (00l)-oriented polycrystalline structures, and the remnant polarization of BNTMg film is larger than that of BNTMn film and the coercive field of BNTMn film is lower than that of BNTMg film. The values of 2P_r and 2E_c of BNTMg and BNTMn are 28 μC/cm² and 212 kV/cm, and 15 μC/cm² and 175 kV/cm, respectively. The relevant physical mechanisms were pursued.

Bismuth titanate (Bi₄Ti₃O${}_{12}$ or BiTO) is known for its high resistance to dielectric fatigue and relatively large remnant polarization. Owing to these characteristics, it has been applied in FeRAM memory. BiTO is also known to be a potential ionic conductor. In both applications, crystalline defects play an important role. In this work, a standard thermochemical equilibrium procedure is used to analyze defect chemistry in BiTO. The results indicate a strong oxidized state. To obtain a reduced condition, extremely low oxygen partial pressures and high temperatures have to be achieved. Even at normal conditions, results show a relatively high concentration of holes, which is in agreement with the $p$-type leaking experimentally observed, relatively high concentration of oxygen vacancies, which suggest the potential application of BiTO as ion conductor, and relative high concentration of bismuth vacancies, in accordance with the known problem of bismuth volatilization observed during the processing of this material.

We report the unexpectedly excellent dielectric properties of amorphous thin films with compositions in the Bi–Ti–O system. Films were deposited by RF magnetron reactive co-sputtering. In the composition range of 0.5 < $x$ < 0.7, amorphous ${{\text{Bi}}_{1-}}_x$${\text{Ti}}_x$${\text{O}}_y$ exhibits excellent dielectric properties, with a high dielectric constant, ${𝜀}_r$$\sim$ 53, and a dissipation factor as low as tan $\delta$ = 0.007. The corresponding maximum breakdown field reaches $\sim$1.6 MV/cm, yielding a maximum stored charge per unit area of up to 8 $\mu$C/cm². This work demonstrates the potential of amorphous Bi–Ti–O as a high-performance thin-film dielectric material that is compatible with high-performance integrated circuits.

The comparative analysis of the dielectric properties of bismuth-containing pyrochlores with different manifestation of atomic order/disorder was carried out. We examined the dielectric properties (including behavior in electric fields) of two pyrochlore compounds: BZN (presumably a composition close to ${\text{Bi}}_{1.5}$${\text{Zn}}_{0.5}$${\text{Nb}}_{1.5}$${\text{O}}_{6.5})$ ceramics with chemical disorder in both A and B cation sublattices and Bi₂Ti₂O₇ single crystal with fully chemical ordered structure. The fundamental differences between the dielectric properties of the BZN ceramics and Bi₂Ti₂O₇ single crystal were shown. In particular, in the dielectric relaxation behavior (which cannot be described via Arrhenius law in the Bi₂Ti₂${\text{O}}_7)$ or in the influence of the electric fields on the dielectric permittivity (splitting of the field-cooled and zero-field-cooled behaviors was observed for Bi₂Ti₂O₇ below estimated freezing temperature). The results of this study highlights the special role of Bi₂Ti₂O₇ as a candidate material for studying aspects of geometric frustration related with pyrochlore structure in non-magnetic medium and specifies the future directions of research.