Impact of Pt bottom electrode on the properties of ferroelectric Bi3.25La0.75Ti3O12 capacitors

Lanthanum-modified bismuth titanate (Bi_3.25La_0.75Ti₃O₁₂) (BLT) films have been prepared on platinized silicon substrates using sol–gel method. Highly (001) or (111) oriented platinum layers are used as the bottom electrodes of ferroelectric BLT capacitors to study the effects of Pt orientation on the structural and physical properties of BLT films. X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements demonstrate that the microstructure and morphology of BLT films are not strongly affected by the Pt films. BLT film on highly (111) oriented Pt possesses much higher remanent polarization (∼ 8 μC/cm²) than that on highly (001) oriented Pt although the coercive fields of the two kinds of Bi_3.25La_0.75Ti₃O₁₂ films are almost equal.     

Characterizations of trimetallic heteronuclear Bi1−x La x [Fe(CN)6]·n(H2O) complexes and their thermal decomposition products

Heteronuclear Bi_1−x La _x [Fe(CN)₆]·nH₂O complexes were synthesized, and their crystal structures and thermal decomposition process were investigated by X-ray diffraction (XRD), thermogravimetry analysis (TGA), Auger electron spectroscopy (AES) with scanning electron microscope (SEM), and transmission electron microscopy (TEM). The crystal system of the complexes was orthorhombic having n = 4 for x = 0–0.7 and was hexagonal having n = 5 for x = 1.0. Their mixture was confirmed for x = 0.8 and 0.9. The lattice parameters for the orthorhombic increased with increasing the x value for the complexes. The single phase of trimetallic perovskite-type Bi_1−x La _x FeO₃ was obtained by its thermal decomposition at low temperature. The crystal system was hexagonal for BiFeO₃ (x = 0) and orthorhombic for x = 0.1–1.0. In the case of the decomposed perovskite sample, the lattice parameters decreased with increasing x values for Bi_1−x La _x FeO₃. The particle size was ca. 30 nm for Bi_0.2La_0.8FeO₃ obtained by thermal decomposition at 500 °C and it grew with an increase in decomposition temperature. For the Bi_0.5La_0.5FeO₃, AES showed that the elemental distributions of Bi, La, and Fe on the surface were very homogeneous for the sample decomposed at 700 °C.     

Fatigue and retention properties of Bi3.25La0.75Ti3O12 films using LaNiO3 bottom electrodes

Fatigue-free Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films were grown on LaNiO₃ bottom electrodes grown in a microwave furnace at 700 °C for 10 min from the polymeric precursor method. It was found that LaNiO₃ (LNO) bottom electrode with pseudocubic structure strongly promote the formation of (00l) texture of BLT films. The remanent polarization (P_r) and the drive voltage (V_c) were 11 μC/cm² and 1.3 V respectively, and are better than the values found in the literature. The polarization of the Au/BLT/LNO/SiO₂/Si (100) capacitors with a thickness of 280 nm exhibited no degradation after 1 × 10¹⁰ switching cycles at an applied voltage of 5 V with a frequency of 1 MHz. After several tests the capacitors retain 77% of its polarization upon a retention time of 10⁴ s.     

Study of magnetic and magnetocaloric properties of La0.6Pr0.1Ba0.3MnO3 and La0.6Pr0.1Ba0.3Mn0.9Fe0.1O3 perovskite-type manganese oxides

The compositional dependence of the magnetic and magnetocaloric properties of La_0.6Pr_0.1Ba_0.3MnO₃ (LPBMO) and La_0.6Pr_0.1Ba_0.3Mn_0.9Fe_0.1O₃ (LPBMFO) were investigated. Polycrystalline samples were prepared by the standard solid-state reaction method. Temperature-dependent magnetization measurements and Arrott analysis reveal second-order ferromagnetic transitions in both samples with Curie temperature increasing with doping iron from 94 K for LPBMO to 277 K for LPBMFO. Magnetic entropy change \( | {\Delta S_{\text{M}} } | \) was calculated by applying the thermodynamic Maxwell equation to a series of isothermal field-dependent magnetization curves. However, the analysis of the magnetocaloric effect (MCE) using Landau theory of phase transition shows that the contributions to the free energy from the presence of ferromagnetic clusters are strongly influencing the MCE by coupling with the order parameter around the Curie temperature.     

Influence of transition metal element (Co,Ni, Cu) doping on structural,electrical and magnetic properties of Bi<Subscript>0.9</Subscript>Ca<Subscript>0.1</Subscript>FeO<Subscript>3</Subscript> nanoparticles

The multiferroic Bi_0.9Ca_0.1FeO₃, Bi_0.9Ca_0.1Fe_0.9Co_0.1O₃, Bi_0.9Ca_0.1Fe_0.9Ni_0.1O₃, Bi_0.9Ca_0.1Fe_0.9Cu_0.1O₃ samples were prepared by a simple sol–gel method. Rietveld refinement of X-ray diffraction data and Raman spectra reflect a structural phase transition from single phase (rhombohedral, pure BiFeO₃) to two phase coexistence (rhombohedral R3c and cubic Fm-3 m). The structural distortion of Bi_0.9Ca_0.1Fe_0.9Ni_0.1O₃ is very marked. SEM images show the co-doped nanoparticles having an average size of 50 nm. A contribution from the leakage current have been observed in the P–E loops. XPS results reveal that the concentration of Fe²⁺ and oxygen vacancy decreased after transition metal elements (Co, Ni, Cu) doped into Bi_0.9Ca_0.1FeO₃. Moreover Co, Ni doping can enhance the saturation magnetization, while Cu doping can enhance the coercive field in Bi_0.9Ca_0.1FeO₃.     

Electron Spin Resonance Study of Polycrystalline La<Subscript>0.4</Subscript>Bi<Subscript>0.1</Subscript>Ca<Subscript>0.5</Subscript>MnO<Subscript>3</Subscript>

We have inspected the magnetic properties of polycrystalline La_0.4Bi_0.1Ca_0.5MnO₃ using electron spin resonance (ESR) in the temperature range 150–280 K. The temperature dependence of magnetization indicates that the Curie temperature is T _C= 225 K. ESR spectra revealed that the sample is not completely paramagnetic above its Curie temperature through the presence of ferromagnetic interactions in the temperature range 225–270 K which can be attributed to the presence of Griffiths phase in this temperature range. The sample becomes completely paramagnetic above 270 K. The presence of Griffiths phase can be attributed to the disorder induced by the 6 s ² lone pair electrons of Bi³⁺ ions.     

Sol–gel auto-combustion synthesis of PVP/CoFe2O4 nanocomposite and its magnetic characterization

Poly(vinyl pyrrolidone)/CoFe₂O₄ nanocomposite has been fabricated by a sol–gel auto-combustion method. Poly(vinyl pyrrolidone) was used as a reducing agent as well as a surface capping agent to prevent particle aggregation and stabilize the particles. The average crystallite size estimated from X-ray line profile fitting was found to be 20 ± 7 nm. The high field irreversibility and unsaturated magnetization behaviours indicate the presence of the core–shell structure in the sample. The exchange bias effect observed at 10 K suggests the existence of the magnetically aligned core surrounded by spin-disordered surface layer. The reduced remanent magnetization value of 0.6 at 10 K (higher than the theoretical value of 0.5) shows the PVP/CoFe₂O₄ nanocomposite to have cubic magnetocrystalline anisotropy according to the Stoner–Wohlfarth model.     

Chemical mechanical polishing characteristics in (Bi,La)Ti3O12 damascene process for high-density ferroelectric memories

Ferroelectric thin films such as Pb(Zr,Ti)O₃, SrBi₂Ta₂O₉, and Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films have been widely investigated for non-volatile ferroelectric memories. BLT thin films show advantages such as highly fatigue resistance, low processing temperature, and large remanent polarization. The patterning of these ferroelectric thin films with a vertical sidewall and without plasma damage is strongly required. Chemical mechanical polishing (CMP) process was investigated for the vertical sidewall patterning of BLT thin films. Removal rate and within-wafer non-uniformity (WIWNU%) were examined by change of process parameters. Potential of hydrogen (pH) in slurry was varied for an improvement of the removal rate and WIWNU%. Surface roughness of BLT thin films after CMP process for the improvement of densification was inquired into by atomic force microscopy. The excellent performance such as 188.4 nm/min of removal rate, 2.61% of WIWNU%, 0.95 nm of root mean square roughness, and 6.94 nm of peak-to-valley roughness was obtained. This result will lead the CMP process to pattern the BLT thin films for the vertical sidewall without plasma damage.     

The Multiferroic Properties of (Bi<Subscript>0.9</Subscript>Ba<Subscript>0.1</Subscript>)(Fe<Subscript>0.95</Subscript>Mn<Subscript>0.05</Subscript>)O<Subscript>3</Subscript> Films

(Bi_0.9Ba_0.1)(Fe_0.95Mn_0.05)O₃ films were prepared on LaNiO₃-coated surface oxidized Si substrates. XRD and Raman measurements confirm that the (Bi_0.9Ba_0.1)(Fe_0.95Mn_0.05)O₃ film has pure R3c structure. Clear ferromagnetism with saturated magnetization of about 25 emu/cm³ has been observed at room temperature. The ferroelectric properties of the (Bi_0.9Ba_0.1)(Fe_0.95Mn_0.05)O₃ film was confirmed by the observation of the ferroelectric domains and the converse piezoelectric coefficient d ₃₃ versus applied voltage hysteresis loops by piezoelectric force microscopy (PFM). The observation of ferromagnetism and ferroelectricity in (Bi_0.9Ba_0.1)(Fe_0.95Mn_0.05)O₃ films indicates the potential multiferroic applications.     

Tailoring Magnetoelectric Coupling in BiFeO3/La0.7Sr0.3MnO3 Heterostructure through the Interface Engineering

Electric field control of magnetism ultimately opens up the possibility of reducing energy consumption of memory and logic devices. Electric control of magnetization and exchange bias are demonstrated in all‐oxide heterostructures of BiFeO₃ (BFO) and La_0.7Sr_0.3MnO₃ (LSMO). However, the role of the polar heterointerface on magnetoelectric (ME) coupling is not fully explored. Here, the ME coupling in BFO/LSMO heterostructures with two types of interfaces, achieved by exploiting the interface engineering at the atomic scale, is investigated. It is shown that both magnetization and exchange bias are reversibly controlled by switching the ferroelectric polarization of BFO. Intriguingly, distinctly different modulation behaviors that depend on the interfacial atomic sequence are observed. These results provide new insights into the underlying physics of ME coupling in the model system. This study highlights that designing interface at the atomic scale is of general importance for functional spintronic devices.     

Comparison of Pb(Zr,Ti)O3 capacitors sandwiched with conductive La0.5Sr0.5CoO3 and non-conductive Bi3.25La0.75Ti3O12 layers

Ferroelectric capacitors of Bi_3.25La_0.75Ti₃O₁₂/PbZr_0.4Ti_0.6O₃/Bi_3.25La_0.75Ti₃O₁₂ (BLT/PZT/BLT) and La_0.5Sr_0.5CoO₃/PbZr_0.4Ti_0.6O₃/La_0.5Sr_0.5CoO₃ (LSCO/PZT/LSCO) are fabricated, respectively, on Si substrates in order to study the properties of PZT film sandwiched by conductive oxide and non-conductive oxide layers. It is found that the crystallinity of PZT film grown on LSCO electrode is much better than that on BLT film although the growth temperature of BLT/PZT/BLT is 100 °C higher than that of LSCO/PZT/LSCO. Remanent polarization of LSCO/PZT/LSCO capacitors measured at 10 V is 31.1 μC/cm², which is much higher than the value of 19.8 μC/cm² for BLT/PZT/BLT. Both kinds of the capacitors are fatigue-free up to 10¹⁰ switching cycles. The leakage current density measured at 5 V is about 4.7 × 10^− 6 A/cm² and 1.9 × 10^− 5 A/cm² for BLT/PZT/BLT and LSCO/PZT/LSCO, respectively. The differences for the two kinds of capacitors are discussed in the article.     

Synthesis, and study of magnetic properties, of Bi1?xCdxFeO3

Ceramic Bi_1−x Cd _x FeO₃ (x = 0.0, 0.05, and 0.1) samples were prepared by a citrate-gel method. The as-prepared compounds were calcined at 600 °C for 3 h to obtain nearly single-phase materials. The crystal structure, examined by X-ray powder diffraction (XRD) and Rietveld analysis, confirmed that the samples crystallize in a rhombohedral (space group, R-3c no. 161) structure. Magnetic measurements were carried out on the resultant powders from 300 to ~2.5 K. Magnetic hysteresis loops showed a significant increase in magnetization as a result of Cd doping in BiFeO₃.     

Enhancement of ferromagnetic and dielectric properties of lanthanum doped bismuth ferrite nanostructures

Cylindrical-shaped multiferroic Bi_1?xLa_xFeO₃ (x = 0.0, 0.05, 0.1 and 0.15) were synthesized successfully by hydrothermal method. All samples were found to be rhombohedrally distorted perovskite structure. Diameter of the cylindrical particles reduces from ～450 nm for x = 0.0 to ～100 nm for x = 0.1 prepared under the same conditions. The Neél temperature as well as the dielectric constant was also found to increase with the increase in lanthanum content. Lanthanum doping also enhanced the magnetic properties. Magnetization measurements above room temperature show a significant increase in magnetization at around 400 °C. Enhanced magnetic properties due to lanthanum doping are caused by the breakage of spin cycloid as observed by electron spin resonance study.     

The magnetic properties of Bi0.9Ba0.1Fe0.81M0.09Ti0.1O3 solid solutions (M = Co, Mn, Sc, Al)

Solid solutions with general formula Bi_0.9Ba_0.1Fe_0.81M_0.09Ti_0.1O₃ (M = Co, Mn, Sc, Al) together with parental Bi_0.9Ba_0.1Fe_0.9Ti_0.1O₃ were prepared by the traditional solid state reaction method. Their structural, room temperature magnetic, and dielectric properties were investigated. X-ray diffraction analysis indicated that all samples maintained original R3c space group. M–H hysteresis loop of Co³⁺ doped sample saturated at an applied field of 1 T with spontaneous magnetization of 1.735 emu/g, while Mn⁴⁺ substitution enhanced the magnetization of Bi_0.9Ba_0.1Fe_0.9Ti_0.1O₃ less strongly; addition of Sc³⁺ helped decrease magnetic coercive field while Al³⁺ modified sample exhibited paramagnetic M–H hysteresis loop. Differential scanning calorimetry was applied to determine the Neel temperature (T_N) and the T_N for undoped, Co³⁺, Mn⁴⁺, Sc³⁺, Al³⁺ doped solid solutions were 318.1, 324.3, 335.7, 293.9 and 295.8 respectively. Sc³⁺ substitution had little influence on the dielectric properties of Bi_0.9Ba_0.1Fe_0.9Ti_0.1O₃ while Al³⁺ doping improved its dielectric constant. In contrast, Co³⁺, Mn⁴⁺ doped samples showed decreased permittivity but inhibited tan δ at frequencies larger than 30 kHz.     

Low-Temperature Neutron Diffraction and Magnetic Properties of La1.2Sr0.9Ca0.9Mn2O7

The crystal structure and magnetic properties of a typical polycrystalline double-layered manganite, La_1.2Sr_0.9Ca_0.9Mn₂O₇, were examined using neutron diffraction and magnetization techniques. Neutron diffraction was performed at low and room temperatures and the crystal structure was refined using the Rietveld method based on the space group I4/Mmm. Low temperature neutron diffraction and magnetization measurements clearly revealed antiferromagnetic ordering. A neel transition was observed at approximately 150 K.     

Superconductivity in the tetragonal phase of La1.9Bi0.1CuO4+δ annealed under high oxygen pressure

We have investigated the relation between the crystal structure and superconductivity in La_1.9Bi_0.1CuO_4+δ , in which the phase separation observed in La₂CuO_4+δ is suppressed. A phase diagram in theT?δ plane is given for La_1.9Bi_0.1CuO_4+δ with excess oxygen. For very smallδ values, the crystal structure is orthorhombic, and an orthorhombic-tetragonal phase transition occurs markedly atδ ～ 0.03 in the measured temperature range between 13 and 293 K. Superconductivity is observed in the range of 0.04<δ<0.11. This is clear evidence thathigh-T _c superconductivity also appears in the tetragonal phase.     

Investigation of the crystal structure and electrical properties of La3+-doped SrBi2Ta2O9 ceramics

The layered-perovskite ferroelectric ceramics of La³⁺-doped SrBi₂Ta₂O₂ (SBT), with the chemical formula of SrBi_{(2 - x)}La _x Ta₂O₉ (SBLT), have been prepared by the conventional mixed-oxide method. The effect of substitution of La³⁺ for Bi³⁺ in the crystal structure and electrical properties of SBT ceramics was explored with the aid of X-ray diffraction, (T) curve and ferroelectric hysteresis loop measurements. The electrical properties such as dielectric constant () and remanent polarization (P _r) showed a dependence on the crystal structure, and both reached maxima of 243 and 25 C cm^–2, respectively, with 6 at % La³⁺ substitution, accompanying the greatest structure change. Theoretical considerations were presented to suggest that the atomic displacements and the crystal deformation implied by the crystal structure change are responsible for the improvement of electrical properties. On the other hand, degradation of fatigue resistance was observed in SBLT ceramics, which is believed to be caused by the chemical environment change of the perovskite layers arising from La³⁺ substitution on Bi³⁺ sites.     

Enhanced Al/Ta co-doped Li7La3Zr2O12 ceramic electrolytes with the reduced Ta doping level for solid-state lithium batteries

Garnet Li₇La₃Zr₂O₁₂ (LLZO) is a promising solid-state electrolyte (SSE) candidate for advanced solid-state lithium batteries (SSLBs). In this work, Li_6.25La₃Zr_2-yAl_xTa_yO₁₂ (x?=?0.25, y?=?0; x?=?0.2, y?=?0.15; x?=?0.15, y?=?0.3; x?=?0.1, y?=?0.45; x?=?0.05, y?=?0.6) and Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZT_0.6O) ceramic electrolytes, are prepared via a simple sol–gel process. The effect of Al and Ta co-doping levels on the phase, the microstructure and the ionic conductivity of modified LLZO is discussed in detail. Those Al/Ta co-doped LLZO ceramics (LLZATO) with Ta?≥?0.3 per formula unit, are nearly pure cubic structures with a trace of new phases. The ionic conductivities of Li_6.25La₃Zr_1.55Al_0.1Ta_0.45O₁₂ (LLZA_0.1T_0.45O) and Li_6.25La₃Zr_1.4Al_0.05Ta_0.6O₁₂ (LLZA_0.05T_0.6O), are greatly improved by co-doping Al and Ta, benefitting from the emergence of self-grown LiAlO₂ phase, and the microstructure of large grains contacting small grains. Remarkably, the optimal LLZA_0.1T_0.45O delivers a high ionic conductivity of 6.70?×?10^–4 S cm^?1 and a low electronic conductivity?~?9.83?×?10^–8 S cm^?1 at 25 °C. This work provides available enhanced Al/Ta co-doped LLZO ceramic electrolytes with the reduced Ta doping level for solid-state lithium batteries.

     

Effect of V substitution on microstructure and ferroelectric properties of Bi<Subscript>3.6</Subscript>Ho<Subscript>0.4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films prepared by sol–gel method

Bi_3.6Ho_0.4Ti₃O₁₂ and (Bi_0.9Ho_0.1)_4−x/3Ti_3−x V _x O₁₂ (BHTV) (x = 0.3, 1.2, 3.0 and 6.0%) thin films were prepared on Pt/Ti/SiO₂/Si substrates by sol–gel method. The effect of V content on their microstructure and ferroelectric properties were investigated. All the BHTV samples consisted of the single phase of Bi-layered Aurivillius phase. The B-site substitution with high-valent cation of V⁵⁺, in Bi_3.6Ho_0.4Ti₃O₁₂ films, enhanced the remanent polarizations (2P_r) and reduced the coercive field (2E_c). The BHTV film with x = 0.3% exhibited the better electrical properties with 2P_r 45.5 μC/cm², 2E_c 257 kV/cm, good insulting behavior, as well as the fatigue-free characteristic.     

Preparation, proton conduction, and application in ammonia synthesis at atmospheric pressure of La0.9Ba0.1Ga1– x Mg x O3–α

La_0.9Ba_0.1Ga_1–x Mg _x O_3–α (0 ≤ x ≤ 0.25) was prepared by the microemulsion method. A single phase of LaGaO₃ perovskite structure was formed when x was ≥0.15. Electrochemical hydrogen permeation (hydrogen pumping) proved that La_0.9Ba_0.1Ga_1–x Mg _x O_3–α had proton conduction, and the proton conduction was measured by AC impedance spectroscopy method from 400 to 800 °C in hydrogen atmospheres. Among these samples, La_0.9Ba_0.1Ga_0.8Mg_0.2O_3–α has the highest proton conductivity with the values of 9.51 × 10⁻⁴ to 4.68 × 10⁻² S cm⁻¹ at 400–800 °C. Ammonia was synthesized from nitrogen and hydrogen at atmospheric pressure in an electrolytic cell using La_0.9Ba_0.1Ga_0.8Mg_0.2O_3–α as electrolyte. The rate of NH₃ formation was 1.89 × 10⁻⁹ mol s⁻¹ cm⁻² at 520 °C upon imposing a current of 1 mA through the cell.