Effect of Mn doping on the dielectric properties of BaZr<Subscript>0.2</Subscript>Ti<Subscript>0.8</Subscript>O<Subscript>3</Subscript> ceramics

Pure and Mn-doped BaZr_0.2Ti_0.8O₃ ceramics are prepared via the conventional solid state reaction method. The microstructures, dielectric properties, and diffuse transition of Mn-doped BaZr_0.2Ti_0.8O₃ ceramics have been investigated. The results indicate that manganese ions enter the unit cell maintaining the perovskite structure of solid solution. The addition of manganese leads to the decrease of the Curie temperature. The dielectric loss of the Mn-doped BZT ceramics is lower than that of pure BZT ceramics, and decreases as Mn content increases. The diffuseness of the phase transition of Mn-doped BZT ceramics decreases with the increase of Mn content. There is no obvious frequency dispersion around the dielectric constant peaks for Mn-doped BZT ceramics. The coercive electric field and the remanent polarization decreases as Mn content increases.     

Dielectric properties,microstructure and diffuse transition of Al-doped Ba(Zr<Subscript>0.2</Subscript>Ti<Subscript>0.8</Subscript>)O<Subscript>3</Subscript> ceramics

Pure and Al-doped BaZr_0.2Ti_0.8O₃ (short for BZT) ceramics are prepared via the conventional solid state reaction method. The microstructures, dielectric properties, and diffuse transition of Al-doped BaZr_0.2Ti_0.8O₃ ceramics were investigated. These results indicate that aluminum ions enter the unit cell maintaining the perovskite structure of solid solution. The addition of aluminum leads to the change of the Curie temperature. The dielectric loss of the Al-doped BZT ceramics is higher than that of pure BZT ceramics, and increases as aluminum content increases. The diffuseness of the phase transition of Al-doped BZT ceramics weakens with the increasing of aluminum content. There is no obvious frequency dispersion around the dielectric constant peaks for Al-doped BZT ceramics. The coercive electric field (E _C) increases as Al content increases, and the remanent polarization (P _r) of Al-doped BZT ceramics is lower than that of pure BZT ceramics.     

Structure and properties of Ba(Zr<Subscript>0.2</Subscript>Ti<Subscript>0.8</Subscript>)O<Subscript>3</Subscript> ceramics prepared by spark plasma sintering

Ba(Zr_0.2Ti_0.8)O₃ (BZT) ceramics are prepared from spray-dried powder by spark plasma sintering (SPS) and by normal sintering. By the application of SPS, ceramics with >96% relative densities could be obtained by sintering at 1,100 °C for 5 min in air atmosphere. The pellet as sintered by SPS at 1,100 °C was black and conductive. Although SPS was carried out in air atmosphere, the samples were deoxidized by heating the carbon die. By post-annealing at 1,000 °C for 12 h in air, the pellet was oxidized and became white and insulating. Grain growth was suppressed in the ceramics prepared by SPS, and the average grain size was 0.52 μm. The starting powder contained 1.90% carbon, mainly as binder, and the SPS-prepared ceramics and ordinary prepared ceramics contained 0.15 and 0.024% carbon, respectively. The BZT ceramics obtained by SPS and the subsequent annealing at 1,000 °C for 12 h exhibited a mild temperature dependence of their dielectric constant. The field-induced displacement of the BZT ceramics was less hysteretic and smaller than that of the ceramics sintered by the conventional method.     

Effect of samarium and lanthanum co-dopant on the microstructure and dielectric properties of BaZr<Subscript>0.2</Subscript>Ti<Subscript>0.8</Subscript>O<Subscript>3</Subscript> ceramics

The BaZr_0.2Ti_0.8O₃ ceramics with perovskite structure were prepared by solid state reaction method with addition of x La₂O₃ and x La₂O₃?+?0.2 wt% Sm₂O₃ (x?=?0.0, 0.1 and 0.4 wt%). Microstructure and dielectric behaviour of the obtained ceramics were respectively investigated. The compositions of these ceramics demonstrated a single-phase cubic symmetry in a room-temperature X-ray diffraction study. The dielectric constant peak of those samples with addition of x La₂O₃ and x La₂O₃?+?0.2 wt% Sm₂O₃ greatly reduced along with increasing x. Simultaneously, a drastic increase of the values of γ was also observed when x rose, exhibiting a diffuse phase transition. T _m increased along with increasing La content for x La₂O₃ doped BZT20 ceramics, but decreased along with increasing La content for x La₂O₃?+?0.2 wt% Sm₂O₃ doped BZT20 ceramics. Owing to the doping of Sm³⁺, the x La₂O₃?+?0.2 wt% Sm₂O₃ doped BZT20 ceramics have maintained very low and stable dissipation factors under an increasing environment temperature, making them superior candidates for applications.     

Synthesis,dielectric, and hysteresis behaviour of Ba(Nb<Subscript>0.2</Subscript>Ti<Subscript>0.8</Subscript>)O<Subscript>3</Subscript> ceramics and their solid solutions with BaZrO<Subscript>3</Subscript>

Solid state reaction technique was employed to synthesize Ba(Nb_0.2Ti_0.8)O₃ [BNT], and 0.9Ba(Nb_0.2Ti_0.8)O₃ + 0.1BaZrO₃ [BNT + BZ] samples. Sintered pellets were investigated for its dielectric (ε_r and tanδ) properties in the temperature range 100 K–380 K and in the frequency range of 100 Hz–1 MHz. The variation of ε_r and tan δ may be attributed to hopping of trapped charge carriers, which resulted in an extra dielectric response in addition to the dipole response. Hysteresis loop measurements were studied in the temperature regime 295 K–423 K. Loop area shrunk with the increase of temperature that may be due to phase transition from ferroelectric to paraelectric state.     

Effects of bottom electrodes on dielectric properties of epitaxial 2% Mn doped Ba(Zr<Subscript>0.2</Subscript>Ti<Subscript>0.8</Subscript>)O<Subscript>3</Subscript> thin films

2 mol% Mn doped Ba(Zr_0.2Ti_0.8)O₃ (Mn-BZT) thin films were prepared by pulsed laser deposition (PLD) on single crystal oxide substrates LaAlO₃(001) and MgO(001), with conductive oxide bottom electrodes LaNiO₃ and SrRuO₃, respectively. Both the Mn-BZT films and the bottom electrode films could be c-axial oriented with a cube-on-cube arrangement on the corresponding substrates. The dielectric properties measured with parallel plate capacitor configurations of Au/Mn-BZT/LNO and Au/Mn-BZT/SRO revealed that the Mn-BZT film on LNO bottom electrode exhibited comparatively higher dielectric constant, larger dielectric tunability and lower dielectric loss than that on SRO. It could be mainly attributed to the better epitaxial growth characteristics and mismatch stress of Mn-BZT thin film on LNO, as well as less misfit dislocation and the better morphology of LNO bottom electrode.     

Influence of the state of interfaces on the magnitude of the magnetoelectric effect in Co (Ni) films on PbZr<Subscript>0.45</Subscript>Ti<Subscript>0.55</Subscript>O<Subscript>3</Subscript> and GaAs substrates

Co (Ni) films on ceramic lead zirconate titanate (PbZr_0.45Ti_0.55O₃) ferroelectric substrates and single-crystal GaAs piezoelectric substrates are shown to exhibit a giant magnetoelectric response, which reaches 200 V/A at room temperature and mechanical Q of at least 1000. These findings are interpreted in terms of the formation of stable interfaces in thin-film heterostructures owing to good adhesion of dissimilar materials to substrate surfaces after ion beam sputtering/deposition processing. This will allow one to extend the applicability of the magnetoelectric effect at room temperature to commercially available microelectronic materials and integrate related hybrid structures into single-chip signal generation/processing devices.     

Electrochemical properties of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/C and Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/C/Ag nanomaterials

We have prepared and characterized lithium titanate-based anode materials, Li₄Ti₅O₁₂/C and Li₄Ti₅O₁₂/C/Ag, using polyvinylidene fluoride as a carbon source. The formation of such materials has been shown to be accompanied by fluorination of the lithium titanate surface and the formation of a highly conductive carbon coating. The highest electrochemical capacity (175 mAh/g at a current density of 20 mA/g) is offered by the Li₄Ti₅O₁₂-based anode materials prepared using 5% polyvinylidene fluoride. The addition of silver nanoparticles ensures a further increase in electrical conductivity and better cycling stability of the materials at high current densities.     

Dielectric properties of B<Subscript>2</Subscript>O<Subscript>3</Subscript> doped Sm(Co<Subscript>1/2</Subscript>Ti<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> ceramics at microwave frequency

The microwave dielectric properties and the microstructures of Sm(Co_1/2Ti_1/2)O₃ ceramics with B₂O₃ additions (0.25 and 0.5 wt%) prepared by conventional solid-state route have been investigated. The prepared Sm(Co_1/2Ti_1/2)O₃ exhibited a mixture of Co and Ti showing 1:1 order in the B-site. Doping with B₂O₃ (up to 0.5 wt%) can effectively promote the densification of Sm(Co_1/2Ti_1/2)O₃ ceramics with low sintering temperature. It is found that Sm(Co_1/2Ti_1/2)O₃ ceramics can be sintered at 1,260 °C due to the grain boundary phase effect of B₂O₃ addition. At 1,290 °C, Sm(Co_1/2Ti_1/2)O₃ ceramics with 0.5 wt% B₂O₃ addition possess a dielectric constant (ε _r) of 27.7, a Q × f value of 33,600 (at 9 GHz) and a temperature coefficient of resonant frequency (τ_f) of −11.4 ppm/ °C. The B₂O₃-doped Sm(Co_1/2Ti_1/2)O₃ ceramics can find applications in microwave devices requiring low sintering temperature.     

Fabrication of Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite nanofibers by electrospinning

PVA(Polyvinyl alcohol)/chromium nitrate/aluminum nitrate composite nanofibers were prepared by using sol–gel processing and electrospinning technique. By high temperature calcinating the above precursor fibers, Cr₂O₃/Al₂O₃ composite nanofibers were successfully obtained. The fibers were characterized by XRD, IR, and SEM, respectively. The results showed that the crystalline phase and the morphology of the fibers depended on the calcination temperatures.     

Electric properties of Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript>(BIT)–CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> (CCTO) composite substrates for high dielectric constant devices

A study of the effect of the presence of BIT (Bi₄Ti₃O₁₂) in the dielectric and optical properties of the CaCu₃Ti₄O₁₂ (CCTO) is presented. The samples were prepared by the solid state procedure. Mechanical alloying followed by the solid state procedure has been used successfully to produce powders of CaCu₃Ti₄O₁₂ (CCTO) and BIT (Bi₄Ti₃O₁₂) to be used in the composites. We also look at the effect of the grain size of the BIT and CCTO in the final properties of the composite. The samples were studied using X-Ray diffraction, scanning electron microscopy (SEM), Raman and infrared spectroscopy. We also did a study of the dielectric function K and dielectric loss of the samples. The role played by the grain size of CCTO and BIT in the dielectric constant and structural properties of the substrates are discussed. For frequencies below 10 MHz the K value presented by the CCTO100 sample is always higher than the K value presented by the BIT100 sample. At 100 Hz the value of K 1900 for the CCTO100 sample and 288 for the BIT100 sample. However for the composite sample one has an unexpected result. The dielectric constant is higher for all the frequencies under study. At 100 Hz the value of the K is around 10.000 for the BIT10 sample. Which is more than one order bigger compared to the CCTO100 value for the same frequency. Therefore, these measurements confirm the potential use of such materials for small high dielectric planar devices. These composites are also attractive for capacitor applications and certainly for microelectronics, microwave devices (cell mobile phones for example), where the miniaturization of the devices is crucial.     

Electrical conductivity of nanostructured fluorite-like Sc<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript>

Single-crystal and polycrystalline samples of Sc₄Ti₃O₁₂ have been shown to contain nanodomains (10–50 nm) with different degrees of ordering, coherent with the fluorite-like matrix. The oxygen-ion conductivity of this compound has been determined in the range 300–1000°C in air using impedance spectroscopy. The nanostructured single-crystal and polycrystalline samples are close in the activation energy for bulk conduction at both low and high temperatures: ?1.26 and 1.29 eV in the range 300–775°C, ?1.98 and 2.07 eV in the range 775–1000°C.     

Microwave synthesis and sintering characteristics of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript>

CaCu₃Ti₄O₁₂ (CCTO) was synthesized and sintered by microwave processing at 2·45 GHz, 1·1 kW. The optimum calcination temperature using microwave heating was determined to be 950°C for 20 min to obtain cubic CCTO powders. The microwave processed powders were sintered to 94% density at 1000°C/60 min. The microstructural studies carried out on these ceramics revealed the grain size to be in the range 1–7 μm. The dielectric constants for the microwave sintered (1000°C/60 min) ceramics were found to vary from 11000–7700 in the 100 Hz–00 kHz frequency range. Interestingly the dielectric loss had lower values than those sintered by conventional sintering routes and decreases with increase in frequency.     

Chemical solution deposition of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> thin film

CaCu₃Ti₄O₁₂ (CCTO) thin film was successfully deposited on boron doped silica substrate by chemical solution deposition and rapid thermal processing. The phase and microstructure of the deposited films were studied as a function of sintering temperature, employing X-ray diffractometry and scanning electron microscopy. Dielectric properties of the films were measured at room temperature using impedance spectroscopy. Polycrystalline pure phase CCTO thin films with (220) preferential orientation was obtained at a sintering temperature of 750°C. There was a bimodal size distribution of grains. The dielectric constant and loss factor at 1 kHz obtained for a film sintered at 750°C was k ∼ 2000 and tan δ ∼ 0.05.     

Microwave dielectric properties and its compatibility with silver electrode of LiNb<Subscript>0.6</Subscript>Ti<Subscript>0.5</Subscript>O<Subscript>3</Subscript> with B<Subscript>2</Subscript>O<Subscript>3</Subscript> and CuO additions

The influences of B₂O₃ and CuO (BCu, B₂O₃: CuO = 1:1) additions on the sintering behavior and microwave dielectric properties of LiNb_0.6Ti_0.5O₃ (LNT) ceramics were investigated. LNT ceramics were prepared with conventional solid-state method and sintered at temperatures about 1,100 °C. The sintering temperature of LNT ceramics with BCu addition could be effectively reduced to 900 °C due to the liquid phase effects resulting from the additives. The addition of BCu does not induce much degradation in the microwave dielectric properties. Typically, the excellent microwave dielectric properties of ε_r = 66, Q × f = 6,210 GHz, and τ _f  = 25 ppm/^oC were obtained for the 2 wt% BCu-doped sample sintered at 900 °C. Chemical compatibility of silver electrodes and low-fired samples has also been investigated.     

Ultraviolet-assisted cold poling of Pb(Zr<Subscript>0.52</Subscript>Ti<Subscript>0.48</Subscript>)O<Subscript>3</Subscript> films

This paper discusses the advantages of a room-temperature poling procedure during exposure to ultraviolet light for Pb(Zr_0.52Ti_0.48)O₃ (PZT) films. The results of these experiments include the following: for 1.7-µm-thick chemical solution-deposited PZT films, the saturation photocurrent density after a 10 min white light exposure (190–1900 nm) (no DC bias field applied) increased up to 0.066 µA/cm² with increasing Cr thickness of top electrode in Cr/Pt bilayer electrodes. Furthermore, the d_33,f piezoelectric coefficients for UV-poled samples were 40 and 20% higher than those achieved from field-only poling at either room temperature or 150 °C. Additionally, the development of an internal bias field and pinching were investigated in major and minor polarization–electric field loops. It was found that ultraviolet illumination during the poling process produced photoinduced charge carriers that became trapped by local defects and/or grain boundaries in the films.     

Strain-induced artificial multiferroicity in Pb(Zr<Subscript>0.53</Subscript>Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript>/Pb(Fe<Subscript>0.66</Subscript>W<Subscript>0.33</Subscript>)O<Subscript>3</Subscript> layered nanostructure at ambient temperature

Layered nanostructures (LNs) of the commercial ferroelectric Pb(Zr_0.53Ti_0.47)O₃ (PZT) and the natural ferroic relaxor Pb(Fe_0.66W_0.33)O₃ (PFW) were fabricated with a periodicity of PZT/PFW/PZT (~5/1/5 nm, thickness ~250 nm) on MgO substrates by pulsed laser deposition. The dielectric behavior of these LNs were investigated over a wide range of temperatures and frequencies, observing Debye-type relaxation with marked deviation at elevated temperatures (>400 K). High dielectric constant and very low dielectric loss were observed below 100 kHz and 400 K, whereas the dielectric constant decreases and loss increases with increase in frequency, similar to relaxor ferroelectrics. Asymmetric ferroelectric hysteresis loops across UP and DOWN electric field were observed with high remanent polarization (P_r) of about 33 μC/cm². High imprint (~5–7 V across 250 nm thin films) were seen in ferroelectric hysteresis that may be due to charge accumulation at the interface of layers or significant amount of strain (~3.21) across the layers. Room temperature ferromagnetic hysteresis was observed with remanent magnetization 5.32 emu/cc and a coercive field of ~550 Oe. Temperature and field dependent leakage current densities showed very low leakage ~10⁻⁷–10⁻⁵ A/cm² over 500 kV/cm. We observed imprint in hysteresis that may be due to charge accumulation at the interface of layers or active role of polar nano regions (PNRs) situated in the PFW regions.     

Effect of the synthesis technique on the physicochemical properties of Ce<Subscript>0.8</Subscript>(Sm<Subscript>0.75</Subscript>Sr<Subscript>0.2</Subscript>Ba<Subscript>0.05</Subscript>)<Subscript>0.2</Subscript>O<Subscript>2 − δ</Subscript>

A multicomponent solid electrolyte of composition Ce_0.8(Sm_0.75Sr_0.2Ba_0.05)_0.2O_{2 − δ} has been synthesized by three different techniques: solid-state reaction, laser evaporation, and the glycine nitrate process. Its microstructure, sintering kinetics, and electrical properties have been studied in relation to the synthesis technique. Ceramics produced using laser evaporation consisted of submicron (0.2 μm) grains and offered the highest electrical conductivity: 27 × 10⁻³ S/cm at 873 K.     

Electrical Conductivity and Complex Impedance Analysis of Ba<Subscript>2</Subscript>CrMo<Subscript>0.8</Subscript>W<Subscript>0.2</Subscript>O<Subscript>6</Subscript> Double Perovskite

Electrical properties of Ba ₂CrMo_0.8W_0.2O₆ double perovskite were investigated using admittance spectroscopy technique. According to impedance analysis, the material was modeled by an electrical equivalent circuit. Such analysis proves the presence of relaxation phenomenon in the compound. We also found that ac conductivity follows the Jonscher universal power law. Conduction process is found to be dominated by the thermally activated small polaron (SPH). The activation energy values, inferred from dc conductivity and from the temperature dependence of relaxation time, are closed to each other. Such result indicates that conduction process and relaxation phenomenon are related to the same defect.     

Phase transition and electrical properties of gallium- and indium-doped Bi<Subscript>10</Subscript>Ti<Subscript>3</Subscript>W<Subscript>3</Subscript>O<Subscript>30</Subscript>

Polycrystalline samples of gallium- and indium-doped Bi₁₀Ti₃W₃O₃₀ (mixed-layer Aurivillius phase with the Ti⁴⁺ and W⁶⁺ distributed at random over the perovskite-like slabs) have been prepared by solid-state reactions, and their polymorphism and electrical properties have been studied. Doping with both In³⁺ and Ga³⁺ yields limited solid solutions and shifts the ferroelectric phase transition to lower temperatures. The heterovalent substitutions of In³⁺ and Ga³⁺ for Ti⁴⁺ and W⁶⁺ increase the oxygen vacancy concentration and, accordingly, the conductivity of the material relative to the undoped compound.