Ionic Doping Effects in SrBi2Nb2O9 Ferroelectric Ceramics

Ionic doping effects of various ions in Bi-layered ferroelectric SrBi₂Nb₂O₉ (SBN) ceramics were studied. Un-doped and doped SBN ceramics with Ba²⁺, Pb²⁺, Ca²⁺, Bi³⁺, La³⁺, Ti⁴⁺, Mo⁶⁺, and W⁶⁺ ions were made with solid state reactions. Temperature dependent dielectric constants were measured. Ferroelectric transition temperature (T_C) decreased with Ba²⁺ and Pb²⁺ ions but increased with Ca²⁺ ion which substitutes the 12-coordinated Sr²⁺ site. T_C increased with Ti⁴⁺, Mo⁶⁺, and W⁶⁺ ions which substitute the 6-coordinated Nb⁵⁺ sites. With trivalent Bi³⁺ and La³⁺ ions, T_C increased with Bi³⁺ ion but much decreased with La³⁺ ion. These results showed that the ion size plays an important role in ferroelectricity of SBN ceramics.     

Effect of doped Ni2+ on the dielectric properties of NiO-BaTiO3 composites

NiO-BaTiO₃ composites were prepared by sintering BaTiO₃ together with NiO in air at 1300°C. Microstructure and morphology of the composites were detected by XRD and SEM, and the dielectric properties were measured by LCZ meter. The results indicate that the perovskite phase is formed in fact in status of solid solution doped with Ni²⁺, although only a small amount of Ni ions can dissolve into the perovskite phase. Ni doping decreases the formation temperature of the composite without inhibiting the grain growth of the crystalline phase. The dielectric constant decreases sharply and the dielectric loss decreases smoothly with increasing Ni²⁺ below NiO addition of 0.5 wt.%. When NiO addition increases above 0.5 wt.%, the dielectric constant and loss correlate with mixing rule of the two phases. Meanwhile, the replacement of Ni²⁺ for Ti⁴⁺ decreases the Curie temperature of perovskite phase by 30°C.     

Effect of cobalt doping on the dielectric response of Ba0.95Pb0.05TiO3 ceramics

Dielectric response of Ba_0.95Pb_0.05TiO₃ ceramics doped with 0.1 and 1 wt.% of Co₂O₃, synthesized by conventional high-temperature method, was studied in wide temperature and frequency range. The temperature dependences of the real and the imaginary parts of dielectric permittivity of the ceramics were compared with those of BaTiO₃ and Ba_0.95Pb_0.05TiO_3. The addition of Co³⁺ ions results in a broadening of dielectric anomalies related to the transition to paraelectric cubic phase, and the structural transition between the tetragonal and the orthorhombic phases. At low temperatures (125–200 K) the dielectric absorption of Co-doped Ba_0.95Pb_0.05TiO₃ ceramics was found to exhibit relaxor-like properties. The dielectric response has been found to contain the contributions characteristic of fluctuations of the polar nanoregion boundaries and reorientations of the dipole moments between allowed directions in the nanoregions in the rhombohedral and the orthorhombic phases. The behavior speaks in favor of ordering of polar defects in the host lattice of Ba_0.95Pb_0.05TiO₃ in a form polar nanoregions_.     

Piezoelectric properties and dielectric behavior of Bi1/2Na1/2[Ti1−x (Sb1/2Nb1/2) x ]O3 lead-free piezoelectric ceramics

New lead-free piezoelectric ceramics of ABO₃ perovskite type, Bi_1/2Na_1/2[Ti_1−x (Sb_1/2Nb_1/2) _x ]O₃, were synthesized by conventional solid state reaction. The effect of the replacement of complex ions of (Sb_1/2Nb_1/2)⁴⁺ in the B cationic site on structural and electrical properties was investigated. The XRD analysis showed that all samples exhibited a single phase of perovskite structure. Piezoelectric and dielectric measurement revealed that the substitution of (Sb_1/2Nb_1/2)⁴⁺ ions lead to an increase in piezoelectric constant(d ₃₃), electromechanical coupling factor(k _t), relative dielectric constant(ɛ _r),and loss tangent (tanδ), while excess of (Nb_1/2Sb_1/2)⁴⁺ ions results in a decrease in d ₃₃, k _t, ɛ _r, but an increase in tanδ. Temperature dependence of dielectric constant ɛ _r measurement indicated these compounds were relaxor ferroelectric. At low frequency and high temperature, dielectric constant increased sharply attributed to the superparaelectric clusters after (Sb_1/2Nb_1/2)⁴⁺ ions substitution.     

Fabrication of AMO4 (A = Ba, Sr, Ca M = Mo, W) films on M substrate by solution reaction assisted ball rotation

An alkaline earth molybdates and tungstates, such as AMoO₄ and AWO₄, films have been successfully fabricated on the respective metal substrate in AOH (A = Ba, Sr, Ca) solutions by a ball rotation-assisted solution reaction at room temperature. This film consists the polyhedral crystals of AMO₄ with an average grain size of 8 μm. The dissolution of substrate surface was mainly controlled by the concentration of H₂O₂ oxidizing agent and ball rotation to form MO₄ ^{2 −} in the solution. AMO₄ was deposited on the substrate by the reaction between MO₄ ^{2 −} and A^{2 +} ions without any high energy or high temperature treatment. Also, the mass transport of alkaline earth ions on to the solid/solution interface was improved as a result of the vigorous solution agitation by the ball rotation. Therefore, the deposition rate of the AMO₄ films was accelerated by the ball rotation. A decrease in the grain size of the film was observed incase of an excessive ball rotation.     

Dielectric anomalies of Pb0.7La0.2TiO3-based perovskite

Dielectric transitions from normal ferroelectric to relaxor-like and then to quantum paraelectric-like behaviour were observed by substituting 10 to 60% of Ca²⁺ for Pb²⁺ into A-site of Pb_0.7La_0.2TiO₃ with the required stoichiometry of Pb_0.7(1−x)Ca_0.7x La_0.2TiO₃ (PCLT). The quantum ferroelectric relation that commonly applies to SrTiO₃-based perovskites, T _maxα (X − X _c )^1/2, fails to describe the observed dielectric anomalies in PCLT, whereby the transition temperature vanishes with a finite slope. Quantum ferroelectric behaviour that exhibits a sharp dielectric peak but violates the Curie-Weiss law was not observed throughout the composition range studied. Unlike the typical quantum paraelectric SrTiO₃, the quantum paraelectric-like behaviour observed for PCLT with x = 0.55 and 0.60 exhibit negative transition temperatures, as shown by the fittings to both the Curie-Weiss and Barrett’s relations. Thermal hysteresis was surprisingly observed in substituted PCLT with x = 0.30 and 0.40 that exhibit frequency dispersive relaxation. To establish a correlation between the dielectric anomalies and structural parameters, analyses on global and local perovskite lattices were carried out using X-ray diffraction technique and micro-Raman spectroscopy.     

Preparation of a sensor substrate using functionalized mesoporous silica on a gold film for surface plasmon resonance (SPR) spectroscopy

The use of surface plasmon resonance (SPR) spectroscopy has been applied to a wide variety of fields such as biosensors and surface analysis instruments. In general, a SPR substrate is prepared using self-assembled monolayer (SAM) method of organic molecules as receptor for the target on a layer of gold or silver. However, mesoporous inorganic materials such as SBA-15 have benefits as sensor substrate for SPR. Mesoporous silica has a large surface area which receptor molecule can be attached and has a rigid body which has an excellent stability in the extreme condition compared to organic sensing layer. We prepared an organic modified mesoporous silica and successfully immobilized it on a gold surface, in an attempt to use as a substrate for SPR spectroscopy. For the comparison of sensitivity of prepared substrate, Pt²⁺ detection was selected as a model system. Substrate prepared in this study exhibited the capability of selective sensing for Pt²⁺ ions.     

Ferroelectric Property and Crystal Structure of KNbO3 Based Ceramics

Rietveld refinement analysis was carried out to obtain the knowledge on the solid solution structure of the La and Fe co-doped KNbO₃ ceramics. The diffraction data was well fitted with tetragonal space group P4mm, and showed that La and Fe located at K and Nb sites in KNbO₃ perovskite, respectively. The sum of both occupancy ratios agreed almost well with the doping content. Furthermore, the effects of MnO₂ addition on the ferroelectric properties and crystal structure of the La and Fe co-doped KNbO₃ ceramics were investigated. MnO₂ addition strongly affected the ferroelectric and piezoelectric properties, because the valence of Mn ions changed from Mn^{4 +} to some extents of Mn^{3 +} and Mn²⁺, which were suggested by XAFS analysis.     

Effect of La3+ substitution on microwave dielectric properties of (Pb0.5Ca0.5)(Fe0.5Nb0.5)O3 ceramics

Microwave dielectric properties of the [(Pb_0.5Ca_0.5)_1?x La_2x/3](Fe_0.5Nb_0.5)O₃ and [(Pb_0.5Ca_0.5)_1?x La _x ](Fe_0.5Nb_0.5)O₃ ceramics were investigated as a function of La³⁺ content $ {\left( {0.0 \leqslant \times \leqslant 0.2} \right)} $ . A single perovskite phase was detected in [(Pb_0.5Ca_0.5)_1?x La_2x/3](Fe_0.5Nb_0.5)O₃, while Pb₃Nb₄O₁₃ were detected as a secondary phase in [(Pb_0.5Ca_0.5)_1?x La _x ](Fe_0.5Nb_0.5)O₃ beyond x?=?0.05 due to the excess of unbalanced charge. The amount of Pb₃Nb₄O₁₃ was proportional to the unbalanced charge. Qf value of [(Pb_0.5Ca_0.5)_1?x La_2x/3](Fe_0.5Nb_0.5)O₃ decreased remarkably with La³⁺ substitution due to the increase of oxygen vacancy. For [(Pb_0.5Ca_0.5)_1?x La _x ](Fe_0.5Nb_0.5)O₃ ceramics, dielectric constant and Qf value increased with La³⁺ content up to x?=?0.03 due to an increase of density and grain size. Temperature coefficient of resonant frequency (TCF) was depended on B-site bond valence in single perovskite phase.     

Electrical Conduction and Magnetoelectric Effect in CuFe1.8Cr0.2O4–Ba0.8Pb0.2TiO3 Composites

Magnetoelectric composites of CuFe_1.8Cr_0.2O₄– Ba_0.8Pb_0.2TiO₃ were prepared using high temperature solid-state reaction technique. X-ray structural analysis of these composites confirms the presence of both the phases in the composite. Detailed studies of dielectric properties (, tan and _ac ) as a function of frequency (100 Hz to 1 MHz) and temperature (30°C to 250°C) show that these compounds exhibit diffuse ferroelectric phase transitions. Results of ac conductivity, dc resistivity and thermoelectric power measurements show that conduction occurs by hopping of charge carriers. The magnetoelectric effect has been studied as a function of intensity of magnetic field. The electrical polarisation was induced in piezoelectric (Ba_0.8Pb_0.2TiO₃) phase as result of strain induced in the ferrite (CuFe_1.8Cr_0.2O₄) phase by the applied magnetic field. The Jahn-Teller distortion caused in the ferrite lattice by Jahn-Teller ions like Cu²⁺ and Cr³⁺ is also responsible for the elastic coupling of strain to the Ba_0.8Pb_0.2TiO₃ phase.     

Phase transition behaviors of (Na1/2Bi1/2)1−x TiPb x O3 thin films

Ferroelectric thin films of (Na_1/2Bi_1/2)_1?x TiPb _x O₃ have been synthesized via a sol–gel route. Structural changes of the films were investigated by using X-ray diffraction (XRD) and Raman spectroscopy over the composition range 0?<?x?<?0.9. There occur different nano-sized clusters in the films. More interestingly, in contrast to the previously reported results on (Na_1/2Bi_1/2)_1?x TiPb _x O₃ bulk ceramics, the ferroelectric thin films exhibit a rhombohedral–tetragonal structure change at x?=?0.4–0.5, together with a long range tetragonal symmetry at x?≥?0.8. The unique phase transition behaviors are discussed in relation to the growth of Pb²⁺TiO₃ clusters upon the substitution of Pb²⁺ for Na⁺/Bi³⁺ cations in the (Na_1/2Bi_1/2)_1?x TiPb _x O₃ films.     

Mechanoluminescence of Ca2MgSi2O7: Eu2+, Dy3+ Phosphor by Impulsive Deformation

Di-calcium magnesium silicate phosphor doped with Eu²⁺ and Dy³⁺ was prepared using solid state reaction technique under a reducing atmosphere. Prepared sample suffered an impulsive deformation with an impact of a piston for mechanoluminescence (ML) investigations. A temporal characteristic of ML of the phosphor was observed, which expressed single sharp peak with a long decaying section. In order to investigate about the luminescence centre responsible for ML peak, ML spectrum of the same phosphor was also observed. ML spectrum recorded shown similarity in shape as well as peak wavelength with Photoluminescence (PL) spectrum that verifies the existence of single emission centre due to the transition of Eu²⁺ ions i.e. transitions from any of the sublevels of 4f⁶5d¹ configuration to ⁸S_7/2 level of the 4f⁷ configuration. Decay rates for different impact velocities were also calculated using curve fitting technique. Time of ML peak and rate of decay did not change largely with respect to increasing impact velocity of the load and peak ML intensity varied linearly. Increasing impact velocity causes more number of Eu²⁺ ions to get excited to the higher energy level, subsequently de-excitation of more Eu²⁺ ions occurs. This gives rise to increase in ML intensity.     

Effect of additives on Cu electrodeposits: electrochemical study coupled with EQCM measurements

The effect of polyethylene glycol (PEG) and chloride ions on Cu electrodeposition mechanism is investigated. Using blank electrolyte, electrochemical measurements show that PEG adsorbs more or less on the electrode surface depending on the nature of this surface (copper, gold). Alternative current techniques and electrochemical quartz crystal microbalance (EQCM) experiments are performed at open circuit and under polarisation. They show that the PEG adsorption on the Cu electrode is weak at open circuit, but increases under polarisation. In complementary EQCM tests made on Au and on electrodeposited Cu, we conclude that the H₂ gas production reduces the apparent mass of the gold surface. In contrary on Cu, H₂ entrapped in the Cu deposit increases the mass. In all cases, there is an important mass hysteresis. Whatever the substrate, the addition of PEG + Cl⁻ to solution has a beneficial effect by reducing this hysteresis due to the H₂ production. For Cu electrolytes, the PEG addition to solution has little effect, while the simultaneous PEG + Cl⁻ addition inhibits both the Cu²⁺ reduction current and the mass increase. Atomic force microscopy (AFM) images made on the deposits confirm the beneficial effect of the two additives in solution.     

Effect of Ba2+ – Sr2+ co-substitution on the structural and dielectric properties of Lead Titanate

Growing interest in developing new materials for device applications led to study of ferroelectric oxides in a wide range and variety of compositions. In the present work, polycrystalline samples of lead barium strontium titanate (Pb_1-xBa_0.5xSr_0.5xTiO₃) solid solution system have been synthesized. Phase formation studies and crystal structure analysis were carried out by X ray diffractometry at room temperature, which suggested formation of single phase compound with tetragonal structure up to x?=?0.8 and cubic structure for x?=?1.0. The XRD pattern has been analyzed by employing Rietveld method. The phase transition in the system was confirmed by Differential Scanning Calorimetry (DSC). Samples with 0.0????x????0.8 are in ferroelectric state whereas with x?=?1.0 is found to be in paraelectric state at room temperature. Co-substitution of Ba²⁺ and Sr²⁺ into lead titanate shows reduction in anisotropy as well as porosity. The dielectric studies of the system as a function of temperature and frequency were carried out in the range 323?K to 773?K and 100?Hz to 1?MHz respectively. Variation of dielectric constant and loss tangent with temperature shows peaking effect near Curie temperature. Frequency dependant dielectric studies clearly show that the dielectric constant and loss tangent decrease exponentially with increased frequency.     

Pyroelectric infrared sensors made of La-modified PbTiO3 thin films and their applications

Abstract

High sensitive pyroelectric infrared (IR) sensors have been fabricated by using c-axis oriented La-modified PbTiO₃ (Pb_1–xLa_xTi_1?x/4O₃, PLT) thin films. The PLT thin films were deposited on (100)-cleaved MgO single crystal substrates by intermittent rf-magnetron sputtering method. The PLT thin films have high figures of merit for IR sensor without a poling treatment. High performance pyroelectric IR sensors (single element type and linear array type) were fabricated by using PLT (x=0·1, γ=5·5x10^?8 C/cm²K, ?_r=200) thin films. The sensors have remarkably high D* of 3–6x10⁸ cmHz^1/2/W and very fast response. A new compact IR sensing system using the linear array sensor (8 elements) has been developed for a new type of room air-conditioner. This system can measure thermal distribution (8x64) by horizontal scanning of the vertical linear array. Image processing with neural network concept makes possible high-accuracy using a few data from the sensor elements. This sensing system provides ‘‘smart airconditioning'’to improve the comfortable control.     

Structural disorder in BZN-based pyrochlores

Careful structural investigations have been carried out on the Bi_1.5ZnNb_1.5O₇ based dielectric system (of A ₂ B ₂O₇ pyrochlore structure type) in an attempt to understand the origin and tolerance of relaxor behavior in such materials. A highly structured, characteristic diffuse intensity distribution was observed in electron diffraction patterns, which arises from static disordering caused by local short range ordering of Bi and Zn ions on the pyrochlore A sites and associated structural relaxation of the O’A ₂ sub-structure. This structural disordering is not affected by B site substitution of the Nb⁵⁺ ions by Sn⁴⁺ or Ti⁴⁺ ions. The result is of significance for optimizing the dielectric properties of bismuth-based advanced ceramics.     

Ionic conduction and crystal structure of aluminum doped NASICON-type LiGe<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> glass-ceramic crystallized at different times and temperatures

In this communication, NASICON-type glass-ceramic (lithium germanium phosphate, LiGe₂(PO₄)₃) was prepared as lithium super ionic conductor using aluminum as dopant for ionic conduction improvement. The solid solution was Li_1?+?xAl_xGe_2-x(PO₄)₃ (x?=?0.5) that Ge⁴⁺ ions were partially substituted by Al³⁺ ions in crystal structure. Initial glasses were converted to glass-ceramics at different times and temperatures for maximum ionic conduction achievement. The crystals were characterized by X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Energy-Dispersive X-ray spectroscopy (EDX), Differential Scanning Calorimetry (DSC) and Complex Impedance Spectroscopy (CIS) methods. The maximum lithium ion conductivity for glass-ceramic, 5.32?×?10^?3 S/cm at 26 °C was obtained for specimen crystallized at 850 °C for 8 h with minimum activation energy of 0.286 eV. Increasing the crystallization temperature results in secondary phase formation in grain boundary and increasing in crystallization time results in microcracks formation in specimen. Both phenomena decreased the ionic conductivity.     

Photoluminescence properties of a green to red-emitting Eu3+, Tb3+ co-doped CaBi2Ta2O9 ferroelectrics

The CaBi₂Ta₂O₉ bismuth layered-structure ferroelectrics doped with rare earth ions Eu³⁺ and Tb³⁺, or co-doped with Eu³⁺/Tb³⁺ were prepared by the conventional solid-state reaction method. The microstructure and photoluminescence properties of CaBi₂Ta₂O₉: Eu³⁺, CaBi₂Ta₂O₉: Tb³⁺ and CaBi₂Ta₂O₉: Eu³⁺/Tb³⁺ were investigated. The XRD patterns demonstrate that the rare earth ions have been effectively doped into CaBi₂Ta₂O₉ host lattices. The photoluminescence properties of CaBi₂Ta₂O₉ with different activator ions are researched in details. The novel red and green light emissions were observed under the excitation of blue and near-UV light. Notably, tunable emissions and a warm-white color have been achieved in the Eu³⁺ and Tb³⁺ co-doped CaBi₂Ta₂O₉ powders. These results suggest that CaBi₂Ta₂O₉: Eu³⁺, CaBi₂Ta₂O₉: Tb³⁺ and CaBi₂Ta₂O₉: Eu³⁺/Tb³⁺ could be novel luminescence materials. It is also expected that rare earth doped CaBi₂Ta₂O₉ ferroelectrics can find potential applications in new multifunctional photoluminescence ferroelectric devices.     

Redox behavior and electrical properties of Sr and Zr substituted BaTiO3

The oxidation and reduction behavior of Sr and Zr substituted BaTiO₃ has been studied by measuring equilibrium electrical conductivities as a function of oxygen activity. The substitution of Sr⁺² and Zr⁺⁴ for Ba²⁺ and Ti⁴⁺ in BaTiO₃ shifted the conductivity profiles to lower oxygen partial pressures. The replacement of Ba with smaller Sr ions suppresses the oxygen dissociation from the lattice, consequently increasing the enthalpy for reduction (ΔH _n ), whereas the Sr substitution requires less energy for oxidation (ΔH _p ). The increase in reduction enthalpy at lower oxygen activities suppresses the formation of oxygen vacancies, the materials becoming resistant to reduction process. Such a reduction resistant behavior gave rise to greater electrical resistivities for (Ba_0.9Sr_0.1)(Ti_0.9Zr_0.1)O₃ than for Ba(Ti_0.9Zr_0.1)O₃ when the samples were sintered at lower P(O₂).     

Effect of Co-substitution on the structure and magnetic properties of MnZn power ferrite

MnZn power ferrites with a composition of Mn_0.681-xZn_0.246Fe_2.073Co_xO₄ were prepared by conventional ceramic technique. The samples were sintered in a computer-driven furnace at 1320 °C for 4 h. Then the influences of Co-substitution on the crystalline structure, microstructure and the magnetic properties of MnZn power ferrite were studied. It shows that Co-substitution has not changed the structure of MnZn ferrite, but improved the crystallization. With the increase of Co substitution content, Co²⁺ ions firstly replace Mn²⁺ ions and then replace Fe³⁺ ions. And at room temperature, the initial permeability increases with the increase of Co-substitution content. Co-substitution can also reduce the porosity and the power loss. In addition, the corresponding temperature of the minimum power loss shifts to a lower temperature.