Suppression Of Oxygen Vacancies Research Articles

Room-temperature ferromagnetism in Gd and Sn co-doped bismuth ferrite nanoparticles and co-doped BiFeO3/MXene (Ti3C2) nanohybrids for spintronics applications

Room-temperature ferromagnetic materials are required for new flourishing spintronic technology. Synthesis of co-doped (Gd, Sn) BiFeO3 (Bi1-xGdxFe1-ySnyO3, x = 0, 0.1, 0.15, 0.25; y = 0.1) nanoparticles and nanohybrid co-doped BiFeO3/MXene system as well as structural morphological, electronic and ferromagnetic properties are analysed. XRD patterns showed distorted rhombohedral structure of pure BFO which undergoes transition of phase from rhombohedral to orthorhombic structure due to the Gd substitution in BFO. From SEM, clear voids and porous network can be observed and agglomeration of particles can be due to the addition of Gd substitutions to the BFO. The hysteresis behaviour was revealed for different concentrations of magnetically active Gd added in BFO host, increments in the concentration of Gd resulted in enhanced saturation magnetizations for different samples mainly due to the alteration in antiferromagnetic ordering at the particle's surface, phase transition due to the Gd substitution, collapse of space modulated spin, suppression of oxygen vacancies and increase in number of Fe ions. The magnetization of the hybrid system shows a clear hysteresis behaviour but with decreased saturation magnetization which is attributed to the super exchange effect at the BGFSO and Ti3C2 interface. Unlike the other reports on magnetism in 2D materials, the present work presents magnetic effect in MXene hybrid system which opens up new material designs for 2D spintronics.

Enhanced Ferroelectric Properties and Insulator-Metal Transition-Induced Shift of Polarization-Voltage Hysteresis Loop in VOx-Capped Hf0.5Zr0.5O2 Thin Films.

A capping layer is known to be critical for stabilizing the ferroelectric (FE) orthorhombic phase (o-phase) in a HfO2-based thin film. Here, vanadium oxide (VOx), a functional oxide exhibiting the insulator-metal transition, is used as a novel type of a capping layer for the Hf0.5Zr0.5O2 (HZO) thin film. It is demonstrated that the VOx capping layer (VCL) can enhance the FE properties of the HZO thin film comprehensively. Specifically, the HZO thin film with a VCL shows large remanent polarization (2Pr ≈36.9 μC/cm2), relatively small coercive field (Ec ≈1.09 MV/cm), high endurance (up to 109 cycles), and long retention (>105 seconds). The enhanced FE properties may be attributed to the VCL-induced stabilization of the FE o-phase and suppression of oxygen vacancies at the interface. Furthermore, the HZO thin film with a VCL exhibits a successive rightward shift of polarization-voltage (P-V) hysteresis loop as the temperature increases. This is well correlated with the insulator-metal transition in a VCL, which can modulate the interfacial built-in field and thus cause the P-V loop shift. It is therefore demonstrated that a VCL not only enhances the FE properties of HZO thin films but also provides a temperature degree of freedom to modulate the FE properties, which may open up a new pathway to develop HfO2-based FE memories with high performance and novel functionalities.

Suppression of Ti3+ generation in Ba3.75Nd9.5Ti17.5M0.5O54 (M = Cu, Cr, Al, Mn) ceramics

The suppression of Ti3+ generation in Ba3.75Nd9.5Ti18O54 (BNT) ceramic sintered at high temperature is investigated by substituting four metal ions M (M = Cu2+, Cr3+, Al3+, Mn4+) for Ti4+ at B-site. The XRD results show BNT ceramics substituted by M are formed as single tungsten-bronze type structured phase. All M substitutions have significant impact on the suppression of oxygen vacancies (VO••) and Ti3+ generation in BNT ceramic, which is confirmed by XPS results. BNTM ceramics have noticeable increase of Q×f values and decrease of positive τf values, but tiny decline in εr values. The SEM images of BNTM ceramics show a promotion of grain size by substituting M for Ti, which may be conducive to improvement on Q×f values.

Evolution of the composition, structure, and piezoelectric performance of (K1-xNax)NbO3 nanorod arrays with hydrothermal reaction time

Lead-free (K,Na)NbO3 (KNN) nanorod arrays were synthesized with the assistance of a Nb: SrTiO3 single-crystal substrate through the hydrothermal process. The evolutions of the morphology, composition, and structure of the as-synthesized KNN nanorods with the increase in reaction time were investigated. The results confirmed that the increase in reaction time up to 3 h led to the increase in the length and aspect ratio of the well-aligned KNN nanorods. All samples have K-rich orthorhombic crystal structures, while the diffraction peaks shifted towards a higher degree. The peak shifts should be attributed to the increase in the Na content in the KNN lattice, which could decrease the lattice parameters owing to the small ionic radius of Na+ than that of K+. Moreover, the increase in reaction time also resulted in the suppression of oxygen vacancies on the surface of the KNN nanorods. These evolutions of the composition and crystal structure, as well as the decrease in the defect content, lead to great enhancement of the nanorod's piezoelectric response, as their d33 value was increased from 19 to 64 pm/V. These results demonstrated the significant impact of reaction time on the hydrothermal growth of high-performance lead-free KNN one-dimensional nanomaterials.

2D hole gas seen.

A p-type metallic sheet forms between two oxide insulators, LaAlO3 and SrTiO3. Suppression of oxygen vacancies in SrTiO3 plays a critical role in forming this sheet.

Amorphous Oxide Thin Film Transistors with Nitrogen-Doped Hetero-Structure Channel Layers

The nitrogen-doped amorphous oxide semiconductor (AOS) thinfilm transistors (TFTs) with double-stacked channel layers (DSCL) were prepared and characterized. The DSCL structure was composed of nitrogen-doped amorphous InGaZnO and InZnO films (a-IGZO:N/a-IZO:N or a-IZO:N/a-IGZO:N) and gave the corresponding TFT devices large field-effect mobility due to the presence of double conduction channels. The a-IZO:N/a-IGZO:N TFTs, in particular, showed even better electrical performance (µFE = 15.0 cm2・V−1・s−1, SS = 0.5 V/dec, VTH = 1.5 V, ION/IOFF = 1.1 × 108) and stability (VTH shift of 1.5, −0.5 and −2.5 V for positive bias-stress, negative bias-stress, and thermal stress tests, respectively) than the a-IGZO:N/a-IZO:N TFTs. Based on the X-ray photoemission spectroscopy measurements and energy band analysis, we assumed that the optimized interface trap states, the less ambient gas adsorption, and the better suppression of oxygen vacancies in the a-IZO:N/a-IGZO:N hetero-structures might explain the better behavior of the corresponding TFTs.

Effect of Ti Doping to Maintain Structural Disorder in InOx-Based Thin-Film Transistors Fabricated by RF Magnetron Sputtering

The effect of Ti doping in an indium oxide (InOx)-based semiconductor is investigated for the thin-film transistor (TFT) property and crystal structure of the film. InOx and Ti-doped InOx (InTiOx) films deposited by RF magnetron sputtering under the same O2 partial pressure conditions were systematically compared. The TFT behavior of the InOx showed higher conductivity than that of the InTiOx and was drastically changed to metallic conduction after annealing at 150 °C. Under the annealing conditions when the electrical transition to the metallic behavior occurred, the InOx film was crystallized. The X-ray diffraction analysis revealed that the shrinkage of the In2O3 unit cell is pronounced in the case of InOx films. Thus, Ti dopants may play the role as a suppressor for shrinkage of the unit cell, i.e. maintaining neighboring In–In distances, in addition to suppression of oxygen vacancies. The In–In distance, which is related to the overlapping of In 5s orbitals, is considered to be one of the key factor for which InOx-based materials are utilized as conducting films or semiconducting channels.

Amorphous LaZnSnO thin films by a combustion solution process and application in thin film transistors

Amorphous LaZnSnO thin films with different La doping concentration are prepared by a combustion solution process and the electrical performances of thin film transistors (TFTs) are investigated. The influence of La content on the structure, oxygen vacancies, optical and electrical performance of LaZnSnO thin films are investigated. At an appropriate amount of La doping (15 mol.%), LaZnSnO-TFT shows a superior electrical performance including a mobility of 4.2 cm2/V s, a subthreshold swing of 0.50 V/decade and an on/off current ratio of 1.9 × 107. The high performance LaZnSnO-TFT is attributed to the better interface between SiO2 and LaZnSnO channel layer and the suppression of oxygen vacancies by optimizing La content. It suggests that La doping can be a useful technique for fabricating high performance solution-processed oxide TFTs.

Epitaxial BiFe0.95Mn0.05O3 film prepared by sol–gel method combined with rapid thermal annealing

Epitaxial BiFe 0.95 Mn 0.05 O 3 (BFMO) film with room-temperature switching properties is prepared on SrTiO 3 (STO) substrate with a SrRuO 3 (SRO) buffer layer by sol–gel method coupled with rapid thermal annealing (RTA). The remnant polarization and coercive field of SRO/BFMO/SRO capacitor, measured at 455 kV/cm, are 51.8 μC/cm2 and 153.5 kV/cm, respectively. Besides the good fatigue resistance and retention characteristics, the relatively small leakage current density of the capacitor is mainly attributed to the suppression of oxygen vacancies resulting from RTA. Moreover, the SRO/BFMO/SRO capacitor satisfies the Ohmic conduction behavior at fields lower than 90 kV/cm, and the Schottky emission at fields higher than 90 kV/cm.

Evidence of spin-two phonon coupling and improved multiferroic behavior of Bi1−xDyxFeO3 nanoparticles

Rare earth Dy substituted BiFeO3 (Bi1−xDyxFeO3) nanoparticles with x=0.03, 0.05 and 0.10 were prepared by a sol–gel method. Rietveld analysis of the X-ray diffraction patterns and Raman spectroscopy confirmed substitution induced phase transformation from rhombohedral to orthorhombic phase for x=0.10. In Raman spectra, the broad band ranging from 900 to 1400cm−1, associated with strong spin-two phonon coupling behavior, was observed. Magnetic studies showed enhancement in magnetization in which the saturation magnetization of 5.5emu/g for x=0.10 sample has been measured. Dielectric measurements showed magnetoelectric coupling around Neel temperature in all the samples. Conductivity of the samples decreases with increasing Dy concentration, indicating suppression of oxygen vacancies. The change in Bi–O and Fe–O bond lengths with increasing Dy content observed from infrared spectroscopy analysis is also found to be in agreement with Rietveld refinement results.

Magneto-dielectric anomaly in (Bi0.95Nd0.05)(Fe0.97Mn0.03)O3 electroceramic

ABSTRACTWe report magneto-dielectric anomaly of the multiferroic (Bi0.95Nd0.05)(Fe0.97Mn0.03)O3 (BNFM) ceramic near Néel temperature. The ceramic pellets were synthesized by conventional solid state reaction route. X-ray diffraction patterns revealed that most of the peaks shifted slightly towards higher Bragg’s angle compared to those of pure BiFeO3 and also confirmed the formation of rhombohedral phase. It also suggests that the small chemical substitution of Nd and Mn atoms at Bi and Fe sites of BiFeO3 (BFO) perovskite respectively does not alter the crystal structure. Temperature and frequency dependent dielectric response indicate large dielectric anomaly at 620 K, slightly below the known Néel temperature of BFO. The enhancement in dielectric properties of BNFM ceramic was observed as compared to BFO due to suppression of oxygen vacancies by the doping. Temperature dependent dielectric response in conjunction with Raman and thermo-analytical data show that the BNFM sample presents significant magneto-dielectric response around Néel temperture TN ∼ 620 K.

Structural distortion and enhanced ferroelectric properties of Tb and Cr co-doped BiFeO3 thin films

BiFeO3 and Bi0.92Tb0.08Fe1−xCrxO3 (BTFCO) thin films were successfully prepared on SnO2: F (FTO)/glass substrates by a chemical solution deposition technique. The influences of Tb and Cr co-doping on the structure, the leakage current, charge defects, the dielectric and the ferroelectric properties of the BTFCO thin films were investigated systematically. X-ray diffraction and Raman spectra results clearly reveal the structural distortion in the co-doped thin films. The X-ray photoelectron spectroscopy measurements show the absence of Fe2+ ions indicating the suppression of oxygen vacancies due to Tb and Cr co-doping. The electrical conduction mechanism of the BTFCO thin film is dominated by the Ohmic conduction in the low resistance state and trap-controlled space charged limited current in the high resistance state. With 8 %Tb and 1 %Cr co-doping, the film exhibits the superior ferroelectric (2P r = 105 μC/cm2) and dielectric properties. All the results show the film is very promising in the practical application.

Structural and electrical properties of (Bi0.9Dy0.1)(Fe0.975TM0.025)O3±δ (TM=Ni2+, Cr3+ and Ti4+) thin films

Abstract Pure BiFeO 3 and rare earth and transition metal ions co-doped (Bi 0.9 Dy 0.1 )(Fe 0.975 TM 0.025 )O 3±δ (TM=Ni 2+ , Cr 3+ and Ti 4+ ) thin films were prepared on Pt(111)/Ti/SiO 2 /Si(100) substrates by using a chemical solution deposition method. The changes in the microstructure and the electrical properties with doping elements were investigated. The thin films were well crystallized and randomly oriented, with no detectable impurity and secondary phases. The leakage current densities were reduced and the ferroelectric properties were improved in the co-doped thin films. Among the thin films, the (Bi 0.9 Dy 0.1 )(Fe 0.975 Cr 0.025 )O 3 thin film exhibited well saturated hysteresis loops with remnant polarization (2 P r ) of 36 μC/cm 2 and coercive electric field (2 E c ) of 954 kV/cm at 1000 kV/cm and low leakage current density of 1.91×10 −5 A/cm 2 at 100 kV/cm. The enhanced properties observed in the co-doped thin films could be considered as being the result of the suppression of oxygen vacancies and of the modified microstructure.

Electrical properties in lanthanides substituted (Bi0.9 A 0.1)(Fe0.975Co0.025)O3−δ (A = La, Eu, Gd) thin films

Multiferroic BFO and (Bi0.9A0.1)(Fe0.975Co0.025)O3−δ (A = La, Eu, Gd) thin films were prepared on Pt(111)/Ti/SiO2/Si(100) substrates by using a chemical solution deposition method. The thin films were annealed at 550 °C for 30 min by using a conventional annealing process under a nitrogen atmosphere. Reduced leakage current density and improved ferroelectric properties were observed in the co-doped thin films compared to the BFO thin film. The enhanced properties observed in the co-doped thin films could be considered as being the result of the suppression of oxygen vacancies and of the modified microstructure.

Enhancement in magnetic and dielectric properties of La and Pr co substituted BiFeO3

This report underlines the systematic studies of crystalline structure, magnetic and ferroelectric properties of polycrystalline Bi1−x−yLaxPryFeO3 ceramic samples, in which x changes continuously from 0 to 0.2 for y=0 and y from 0 to 0.2 for x=0.2. X-ray diffraction (XRD) patterns revealed that La and Pr substitution at Bi site in the ceramic eliminates the usual impurity phases completely. Rietveld refinement of the XRD patterns shows that the crystal structure changes gradually from Rhombohedral (R3c) to Orthorhombic (pbnm) with increasing La and Pr concentration. This transition has significant effects on the multiferroic properties of Bi1−x−yLaxPryFeO3 ceramics. Substantial enhancement in magnetization of Bi1−x−yLaxPryFeO3 has been observed and this is found to be correlated with the evolution of structural phase change with doping of Pr in samples having lanthanum concentration of x=0.2. This leads to the suppression of helical spin order. However, the enhancement in magnetic behavior also takes place due to nanocrystallite nature of Bi1−x−yLaxPryFeO3 (x=0.2, y=0.05–0.2). For the nanocrystallites having sizes lower than 62nm, which is the period of spin cycloid, this spin configuration will get destroyed resulting in the enhancement of magnetization. The studies of microstructures employing SEM and TEM revealed that Bi1−x−yLaxPryFeO3 consists of nano size grained microstructures. It is also found that dielectric constant and dielectric loss get improved by La and Pr co-substitution. The dielectric constant for x=0.0, y=0.0 is 81 which changes to 354 for x=0.2, y=0.15 at 100Hz. Dielectric losses are strongly diminished from 0.960 for x=0.0, y=0.0, 0.321 for x=0.2, y=0.0 and to 0.20 for x=0.2, y=0.05 at 100Hz. This improvement in dielectric properties is likely due to the changes of lattice parameters and suppression of oxygen vacancies caused by La and Pr co substitution.

Structural and magnetic characterization of Bi_{0.9}Ca_{0.1}Fe_{0.98}X_{0.02}O_3 (X = Mg, Al, Ti, V) polycrystalline multiferroic compounds

The multiferroic compounds Bi_{0.9}Ca_{0.1}Fe_{0.98}X_{0.02}O_3, X = Mg, Al, Ti, V, were prepared by the solid state reaction method and were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometry, and differential scanning calorimetry. The compounds were found to have the rhombohedral perovskite-like structure, accompanied by the existence of small amounts of the usual impurity phases Bi_2Fe_4O_{9} and Bi_{25}FeO_{40}. The appearance of weak ferromagnetism is due to partial destruction of the spiral spin structure due to lattice distortion and suppression of oxygen vacancies. The magnetic transition temperatures of the compounds are 342, 346, 349, and 345 °C, respectively.

Ferroelectric and Piezoelectric Studies on Mo—Substituted SrBi2Ta2O9 Ferroelectric Ceramics

Samples of compositions SrBi2MoxTa2-xO9 (SBMT), with x = 0.0, 0.025, 0.050, 0.075, 0.10 have been synthesized by solid-state reaction method taking SrCO3, Bi2O3, Ta2O5 and MoO3 in their stoichiometric ratios. X-ray diffraction patterns of the samples confirm the formation of single phase layered perovskite structure in the samples with x up to 0.05. The effect of Mo+6 substitution on the dielectric behavior of SBT was studied by measuring the capacitance and tangential loss using an impedance analyzer (HP 4294A). The temperature dependence of dc conductivity vis-á-vis molybdenum content shows a decrease in conductivity, which is attributed to the suppression of oxygen vacancies. The ferroelectric and piezoelectric studies of the Mo substituted SBT ceramics show that the remanent polarization and d33 values increase with increasing concentration of molybdenum.

Multiferroic Behavior of Sn-Modified BiFeO[sub 3] Thin Films

BiFe x Sn 1-x O 3 (x = 0 and 0.05) (BFSO-x) thin films were grown in situ on Pt/TiO 2 /SiO 2 /Si(100) substrates with a SrRuO 3 buffer layer by off-axis radio-frequency sputtering. The effects of Sn substitution on the multiferroic behavior of BFO thin films were investigated. The leakage current of BFSO-x thin films decreases substantially with the introduction of Sn. The BiFe x Sn 1-x O 3 (x = 0.05) thin film exhibits a lower dielectric loss (tan δ ∼ 0.013) and a much higher dielectric permittivity (e r ∼ 307) as compared with those of BFO thin films, together with the polarization of 2P r ∼ 108.5 μC/cm 2 . The fatigue endurance was greatly improved because of the suppression of oxygen vacancies caused by Sn substitution, while the magnetic behavior was degraded with the introduction of nonmagnetic Sn.

Microstructures and properties of Bi3.25La0.75Ti2.94V0.06O12 ferroelectric thin film deposited by sol–gel method

Bi3.25La0.75Ti2.94V0.06O12 (BLTV) thin film was fabricated on the Pt/TiO2/SiO2/p-Si(100) substrate using sol–gel method. The microstructures and electrical properties of the film after cosubstitution of La and V were investigated. The BLTV thin film shows less highly c-axis oriented than the BIT thin film mainly with fine rod-like grains. Raman spectroscopy shows that TiO6 (or VO6) symmetry decreases and Ti–O (or V–O) hybridization increases for V substitution. The Pr and Ec values of the BLTV thin film are 26.3 μC/cm2 and 98 kV/cm at a voltage of 12 V, respectively. The thin film also exhibits a very strong fatigue endurance up to 1010 cycles and low leakage current density. The excellent properties of the BLTV thin film are attributed to the effective decrease or suppression of oxygen vacancies after La and V cosubstitution in the thin film.

Fatigue-free La-modified PbTiO3 thin films prepared by pulsed-laser deposition on Pt/Ti/SiO2/Si substrates

Fatigue-free 14 mol % La-modified PbTiO3 (PLT) thin films were grown on Pt/Ti/SiO2/Si substrates using pulsed-laser deposition and crystallized by furnace annealing at 600 °C. The 220-nm-thick PLT film capacitors with a Pt top electrode showed excellent ferroelectric properties. The remanent polarization (2Pr) and the coercive field (2Ec) were about 20 μC/cm2 and 70 kV/cm, respectively, and the PLT capacitors did not show any noticeable fatigue up to 3×109 read/write switching cycles at a frequency of 1 MHz and switching voltage of 5 V. By comparing the microstructures, electric, and dielectric properties with those of pure PbTiO3 thin films, the suppression of oxygen vacancies and/or charged defects, and the coral-like microstructures developed in PLT films were attributed to its fatigue-free feature.