Substitution site effect on structural and dielectric properties of La–Bi modified PZT

Substitution site effect of (La:Bi) on the structural and dielectric properties of chemically prepared PZT system Pb_0.92 (La_1−x Bi _x ) _0.08(Zr_0.65Ti_0.35)_0.98O₃ [(a) x = 0.0, (b) x = 0.1, (c) x = 0.2, (d) x = 0.3, (e) x = 0.4 and (f) x = 1.0] have been studied. The samples were prepared by employing a simple co-precipitation technique using nitrates of lead, lanthanum, bismuth, zirconium and titanium isopropoxide. X-ray diffraction studies confirm the formation of phase pure and homogeneous ceramics of rhombohedral symmetry without bismuth addition and a tetragonal symmetry was confirmed for the compounds containing bismuth due to the presence of a doublet (200) peak in these compounds. Scanning electron micrographs shows a uniform grain distribution and the grain size and shape were modified upon bismuth addition. Increase in Bi content causes a decrease in average grain size of the material. Dielectric measurements demonstrate a diffuse type of phase transition and this diffuseness decreases with increasing Bi ion concentration. Composition (A) only showed relaxor type of behaviour. Variation of dielectric constant with temperature shows that both T _c and ε_max increases with increase of Bi concentration. This was explained on the basis of favorable B-site substitution of Bi⁺³ ions and therefore the increased strength of spontaneous polarization. Finally, it is evident that the type of substitution site also has a significant effect on the dielectric properties of the PZT system. All these results suggest that the synthesized ceramics may be suitable for device applications.     

Rare earth titanates ceramics Na2La2Ti3O10: Pr3+ and RE2Ti2O7: Pr3+ (R?=?Gd, Y): sol–gel synthesis, characterization and luminescence

In this work, rare earth (La, Gd, Y) titanate ceramics have been synthesized with a sol–gel process of Ti(OC₄H₉)₄ precursor. It is found that these titanates of the three rare earth ions present two different typical phase composition and crystal structure in spite of the same reaction ratio of the precursors and synthesis conditions, which is taken in the formula Na₂La₂Ti₃O₁₀, and RE₂Ti₂O₇ (RE = Gd, Y), respectively. Besides, the microstructure (particle size and morphology) also show different features for different titanates by SEM. Subsequently, the optical properties (such as ultraviolet–visible diffuse reflectance absorption and photoluminescence) of these titanates activated with Pr³⁺ Na₂La₂Ti₃O₁₀: x mol % Pr³⁺ (x = 0, 0.2, 2, 5, 10, 15), and RE₂Ti₂O₇: x mol % Pr³⁺ (RE = Gd and Y) (both x = 0, 0.2) are compared to study. Especially Na₂La₂Ti₃O₁₀: Pr³⁺ is selected as an example to check that the concentration effect on the luminescence of Pr³⁺, revealing that Na₂La₂Ti₃O₁₀: 0.2 mol % Pr³⁺ possesses the strongest emission.     

Structural and electrical characterization of Bi9?xTi3Mn5+xO27

Solid solutions of bismuth layer structured Bi_9?xTi₃Mn_5+xO₂₇ (x?=?0–3) system were prepared by the solid-state reaction technique using component oxides. X-ray powder diffraction, scanning electron microscopy, dielectric constant, variation of magnetization with magnetic field measurement techniques are used to characterize the compounds. The substitution of Mn³⁺ at Fe³⁺ site in Bi_9?xTi₃Mn_5+xO₂₇ was found to shift the Curie temperature towards the low-temperature region. The relationship between atomic displacement of B site ions (Ti⁴⁺, Fe³⁺, Mn³⁺) and the Curie temperature is discussed. Diffused type of phase transition was observed with a very high loss leading to the formation of soft ferroelectrics.     

Improved dielectric properties in pyrochlore type oxides: Ca3Sm3?xBixTi7Nb2O26.5 (x = 1.0, 2.0 or 3.0) by Bi substitution

Improved dielectric properties are observed in pyrochlore type oxides, Ca₃Sm_3−x Bi_xTi₇Nb₂O_26.5 (x = 1.0, 2.0 or 3.0) by Bi substitution. The dielectric constant increased with increasing Bi concentration. The dielectric constant obtained for Ca₃Bi₃Ti₇Nb₂O_26.5 is 110, whereas, without Bi (Ca₃Sm₃Ti₇Nb₂O_26.5) it is 62 at 100 kHz. The Powder X-ray diffraction analysis reveals that cubic pyrochlore type phase is formed for all the compositions. The experimental results further show that the formation of Bi substituted compounds is complete at a lower temperature than the compounds without Bi. Microstructure studies reveal that the grains formed are acicular when Bi is present in large amounts compared to cuboid grains in samples having no Bi.     

Sol-gel synthesis and photoluminescence of CaTi<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript>: Pr<Superscript>3+</Superscript> phosphors

CaTi_1−x Zr _x O₃: Pr³⁺ phosphors have been synthesized by sol-gel and solid state methods, with x = 1/300, 2/300, 3/300, 4/300, 5/300, 6/300, 7/300, respectively. Powder X-ray diffraction (XRD), UV-visible absorption spectra, photoluminescent spectra (PL), and scanning electron microscopy (SEM) images are used to characterize the powder samples. The inverse absorption at 610 nm appearing in the UV-visible absorption spectra is due to the ¹ D ₂ → ³ H ₄ characteristic emission of Pr³⁺. Changes in the emission spectra at 610 nm were agreed with those in UV-visible absorption spectra. The strongest red excitation obtained from CaTi_1−x Zr _x O₃: Pr³⁺ (x = 4/300) and CaTi_1−x Zr _x O₃: Pr³⁺ (x = 5/300) possesses the strongest emission at 610 nm, similar to the intensities of Ca(Ti_1−x Zr _x )O₃: Pr³⁺ (x = 3/300, 4/300, 6/300), which may be corresponded to the cell parameters of CaTi_1−x ZrxO₃: Pr³⁺.     

Effects of Nb doping on microstructure and properties of Bi4Ti3?xNbxO12 thin films prepared by magnetron sputtering

Bi₄Ti_3−xNb_xO₁₂ ferroelectric thin films were fabricated on p-Si substrates by magnetron sputtering. The effects of Nb doping on microstructure and properties of Bi₄Ti_3−xNb_xO₁₂ films were investigated. Bi₄Ti_3−xNb_xO₁₂ films had the same structure as Bi₄Ti₃O₁₂ with smaller and more uniform grains. The dielectric and ferroelectric properties of Bi₄Ti_3−xNb_xO₁₂ films were improved by Nb doping. Bi₄Ti_3−xNb_xO₁₂ films have better dielectric and ferroelectric properties with P _r = 16.5 μC/cm², E _C < 100 kV/cm, ε _r > 290, low dielectric loss (<0.9%) and clockwise C–V curves with a memory window of 0.9 V when x = 0.03–0.045, while an excessive Nb doping would lead to bad dielectric and ferroelectric properties.     

Microstructure and dielectric properties of Ca1–3/2xBixCu3Ti4O12 (x = 0, 0.05, 0.10, 0.15 and 0.20) ceramics

Influence of bismuth substitution on calcium site in CaCu₃Ti₄O₁₂ has been investigated. Compositions of Ca_1-3/2xBi_xCu₃Ti₄O₁₂ (x = 0, 0.05, 0.10, 0.15 and 0.20) were fabricated by solid-state sintering method. Crystal structure is remained cubic. X-ray diffraction indicates the presence of secondary phase of CuO in CCTO ceramics. Bismuth doping restrains the formation of CuO phase apparently. The grain size of CaCu₃Ti₄O₁₂ ceramics was greatly decreased by Bi³⁺ doping, resulting from the ability of bismuth to inhibit the grain growth. The dielectric and electric properties of CCTO ceramics were found to be influenced by bismuth doping. The fitting results of the complex impedance spectra showed an increase of the resistance of grain and grain boundary by bismuth substitution. Ca_0.70Bi_0.20Cu₃Ti₄O₁₂ showed the highest dielectric constant in the low frequency range. A modest composition such as Ca_0.85Bi_0.10Cu₃Ti₄O₁₂ expressed the optimized dielectric properties of higher dielectric constant (1.3 × 10⁴) and lower dielectric loss (0.06) than pure CCTO. The low and high temperature dielectric loss spectra demonstrate the interfacial polarization of the initial and secondary oxygen ionization, relating with the grain and grain boundary (the electrode contact for Ca_0.70Bi_0.20Cu₃Ti₄O₁₂) respectively.     

Effect of bismuth on the properties of Mn ferrite nanoparticles prepared by co-precipitation method

Nanoparticles of MnBi_xFe_2−xO₄(x = 0.0, 0.02, 0.04, 0.06) have been synthesized by a chemical co-precipitation method. X-ray diffraction analysis (XRD) reveals that bismuth exits in its Bi³⁺ and Bi⁵⁺ state. It was also observed that bismuth substitution enhances the grain growth and density. The dielectric constant (ε′) and the loss tangent (tan δ) increases with increase in bismuth content. Resistivity (ρ) and maximum magnetization (M) was found to decrease with increasing bismuth content.     

The effect of Ba2+ doping on the structure of SrBi4Ti4O15

In this paper, bi-layered structural ferroelectric materials Sr_1–x Ba _x Bi₄Ti₄O₁₅(SBBT) (x=0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) were prepared using sol–gel method. The stable precursors were fabricated by mixing the salts of strontium (Sr), barium (Ba), bismuth (Bi) and titanium butoxide in acetic acid together with ethanolamine as a catalyzer and acetylacetone as a stable agent. The structural evolution of SBBT after Ba²⁺ doping was studied. The experimental results confirm that complete solid solutions of SrBi₄Ti₄O₁₅ and BaBi₄Ti₄O₁₅ are formed. The perovskite lattice will expand after the doping of Ba²⁺ because of the difference of ionic radii of strontium and barium cations, which will lead to increasing of the lattice spacing. With the increase of the content of Ba cations the grain size of SBBT powder increases, the granularity distribution widens and average particle size of SBBT powder also increases. The average particle size of SrBi₄Ti₄O₁₅ and BaBi₄Ti₄O₁₅ is 82.5 and 165.2 nm, respectively.     

Investigations of the Spin Hamiltonian Parameters for the Cu2+ Sites in PrBa2Cu3O6+x and Pr0.5Er0.5Ba2Cu3O6+x

The spin Hamiltonian parameters (the anisotropic g factors g _∥ and g _⊥ and the hyperfine structure constants) for the Cu²⁺ sites in PrBa₂Cu₃O_6+x and Pr_0.5Er_0.5Ba₂Cu₃O_6+x are theoretically investigated using the high order perturbation formulas of these parameters for a 3d⁹ ion in tetragonally elongated octahedra. In these formulas, the tetragonal field parameters are determined from the superposition model and the local structures of the Cu²⁺ sites. The theoretical spin Hamiltonian parameters are in good agreement with the observed values for both systems, and the results show improvements as compared with those based on various adjustable covalency coefficients in the previous work. The larger hyperfine structure constants for PrBa₂Cu₃O_6+x than those for Pr_0.5Er_0.5Ba₂Cu₃O_6+x can be attributed to the weaker covalency due to the relatively longer Cu²⁺– O^[`2]\mathrm{O}^{\bar{2}} bonds in the former.     

Reactions of MnO2, Mn2O3, α-Bi2O3, and Bi12Ti1 – x Mn x O20with Supercritical Isopropanol

Heterogeneous reactions between supercritical isopropanol and metal oxides were studied for the first time. The results demonstrate that Bi₂O₃ is reduced by isopropanol to metallic bismuth, while MnO₂ and Mn₂O₃ are reduced to Mn₃O₄ (hausmannite). The possibility of oxygen extraction from nonstoichiometric oxides is demonstrated by the example of the reaction Bi₁₂Ti_{1 – x} Mn⁵⁺ _x O_{20 +} Bi₁₂Ti_1–x Mn²⁺ _x O_{20 –} .     

The Development of Microstructure and Ferroelectric Properties of Bi<Subscript>4</Subscript>Ti<Subscript>3.96</Subscript>Nb<Subscript>0.04</Subscript>O<Subscript>12</Subscript> Thin Films

Bi₄Ti_3.96Nb_0.04O₁₂ thin films were successfully deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by a sol–gel method and rapid thermal annealing. The effects of Nb-substitution and annealing temperature (500–800°C) on the microstructure and ferroelectric properties of bismuth titanate thin films were investigated. X-ray diffraction analysis reveals that the intensities of (117) peaks are relatively broad and weak at annealing temperatures smaller than 700°C. With the increase of annealing temperature from 500°C to 800°C, the grain size of Bi₄Ti_3.96Nb_0.04O₁₂ thin films increases. The Bi₄Ti_3.96Nb_0.04O₁₂ thin films annealed at 700°C exhibit the highest remanent polarization (2P _r), 36 μC/cm² and lowest coercive field (2E _c), 110 kV/cm. The improved ferroelectric properties can be attributed to the substitution of Nb⁵⁺ to Ti⁴⁺ in Bi₄Ti₃O₁₂ assisting the elimination of defects such as oxygen vacancy and vacancy complexes.     

Magnetic properties of Bi(Fe<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>M<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)O<Subscript>3</Subscript> (M = Mn,Ti)

The magnetic properties of Bi(Fe_{1 − x} M _x )O₃(M = Mn, Ti) solid solutions have been studied in magnetic fields of up to 11.2 × 10³ kA/m, and the composition stability range of the R3c ferroelectric phase has been determined. The results indicate that partial Ti⁴⁺ substitution for Fe³⁺ leads to a transition from a modulated antiferromagnetic state to a homogeneous weakly ferromagnetic ferroelectric state (x = 0.08), whereas the Bi(Fe_1−x ³⁺Mn _x ³⁺)O₃ solid solutions do not exhibit weak ferromagnetism. Charge compensation in is assumed to be ensured by cation vacancies.     

Structure determination at room temperature and phase transition studies aboveT c in ABi4Ti4O15 (A = Ba, Sr or Pb)

The room temperature structure of three compounds belonging to the Aurivillius family (n = 4), ABi₄Ti₄O₁₅ (A = Ba, Sr or Pb) has been analysed. BaBi₄Ti₄O₁₅ crystallizes in a tetragonalI4/mmm space group whereas SrBi₄Ti₄O₁₅ and PbBi₄Ti₄O₁₅ crystallize in the orthorhombic space group A2₁am. The starting model for the Sr and Pb analogues was derived fromab initio methods and refined using the Rietveld method. The cations Ba and Sr are disordered over the Bi sites while the Pb cation is found exclusively in the [Bi₂O₂]²⁺ layers. The TiO₆ octahedra are tilted with the Ti-O bonds forming zigzag chains along the “c” axis. The displacement of Bi atoms along the “a” axis might be responsible for ferroelectricity in these compounds. The high temperature X-ray data aboveT _c indicate no structural transition for A = Ba and Pb while A = Sr transforms to the tetragonal structure.     

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.     

Microstructure and ferroelectric properties of dysprosium-doped bismuth titanate thin films

Bi₄Ti₃O₁₂ (BIT) ferroelectric thin films with Dy³⁺ substitution (Bi_4−xDy_xTi₃O₁₂, x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0, respectively) were grown on Pt(111)/Ti/SiO₂/Si(100) substrates using sol–gel method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed that after annealing at 710 °C for 10 min, all Bi_4−xDy_xTi₃O₁₂ films became polycrystallites. Among all the deposited thin films, the Bi_3.4Dy_0.6Ti₃O₁₂ specimen exhibits improved ferroelectric properties with the largest average remanent polarization (2Pr) of 53.06 μC/cm² under applied field of 400 kV/cm and fatigue free characteristics (16% loss of 2Pr after 1.5 × 10¹⁰ switching cycles), indicating that it is suitable for non-volatile ferroelectric random access memories applications.     

Study of structure and properties of ZnO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Glasses of the ternary system ZnO–Bi₂O₃–P₂O₅ were prepared and studied in two compositional series 50ZnO–xBi₂O₃–(50 − x)P₂O₅ and (50 − y)ZnO–yBi₂O₃–50P₂O₅. Two distinct glass-forming regions were found in the 50ZnO–xBi₂O₃–(50 − x)P₂O₅ glass series with x = 0–10 and 20–35 mol.% Bi₂O₃. All prepared Bi₂O₃-containing glasses reveal a high chemical durability. Small additions of Bi₂O₃ (∼5 mol.%) improve thermal stability of glasses. All glasses crystallize on heating within the temperature range of 505–583 °C. Structural studies by Raman and ³¹P MAS NMR spectroscopies showed the rapid depolymerisation of phosphate chains within the first region with x = 0–15 and the presence of isolated Q⁰ phosphate units within the second region with x = 20–35. Raman studies showed that bismuth is incorporated in the glass structure in BiO₆ units and their vibrational bands were observed within the spectral region of 350–700 cm⁻¹. The evolution of properties and the spectroscopic data are both in accordance with a network former effect of Bi₂O₃.     

High resolution electron microscopy of bismuth oxides with perovskite layers

Layered bismuth oxides of the general formula (Bi₂O₂)²⁺ (A _n−1B_nO_3n+1)²⁻ whereA = Bi or Ba,B = Ti, Fe, W andn = number of perovskite layers have been investigated by high resolution electron microscopy. Lattice images obtained forn = 1 to 6 members show stacking of (n − 1) perovskite layers sandwiched between dark bands due to the (Bi₂O₂)²⁺ layers. It has been possible to resolve the perovskite layer structures in some of the oxides. A highly ordered structure is observed upto then = 3 member, whereas higher members show superstructures, dislocations and stacking faults arising from the side-stepping of (Bi₂O₂)²⁺ layers as well as ferroelectric domain walls. Contribution No. 73 from Materials Research Laboratory.     

Fabrication and ferroelectric properties of sol–gel derived 1–1 intergrowth-superlattice-structured Bi<Subscript>3</Subscript>TiNbO<Subscript>9</Subscript>-Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films

1–1 intergrowth-superlattice-structured Bi₃TiNbO₉–Bi₄Ti₃O₁₂ (BTN–BIT) ferroelectric thin films have been prepared on p-Si substrates by sol-gel processing. The precursor films are crystallized in the desired intergrown BTN–BIT superlattice structures by optimizing the processing conditions. Synthesized BTN–BIT thin films annealed below 750 °C are polycrystalline, uniform and crack-free, no pyrochlore phase or other second phase, and exhibited good ferroelectric properties. As the annealing temperature increases from 600 to 700 °C, both remanent polarization P _r and coercive electric field E _c of BTN–BIT thin films increase, but the pyrochlore phase in BTN–BIT films annealed above 750 °C will impair the ferroelectric properties. The BTN–BIT thin films annealed at 700 °C have a P _r value ~19.1μC/cm² and an E _c value ~135 kV/cm.     

Structure study of Bi4Ti3O12 produced via mechanochemically assisted synthesis

Nanosized bismuth titanate was prepared via high-energy ball milling process through mechanically assisted synthesis directly from their oxide mixture of Bi₂O₃ and TiO₂. Only Bi₄Ti₃O₁₂ phase was formed after 3 h of milling time. The excess of 3 wt% Bi₂O₃ added in the initial mixture before milling does not improve significantly the formation of Bi₄Ti₃O₁₂ phase comparing to stoichiometric mixture. The formed phase was amorphized independently of the milling time. The Rietveld analysis was adopted to determine the crystal structure symmetry, amount of amorphous phase, crystallite size and microstrains. With increasing the milling time from 3 to 12 h, the particle size of formed Bi₄Ti₃O₁₂ did not reduced significantly. That was confirmed by SEM and TEM analysis. The particle size was less than 20 nm and show strong tendency to agglomeration. The electron diffraction pattern indicates that Bi₄Ti₃O₁₂ crystalline powder is embedded in an amorphous phase of bismuth titanate. Phase composition and atom ratio in BIT ceramics were determined by X-ray diffraction and EDS analysis.