Microstructure and dielectric properties of CBS glass-doped Sr0.5Ba0.5Nb2O6 ceramic system

40CaO–20B₂O₃–40SiO₂ (abbreviate as CBS) glass-doped Sr_0.5Ba_0.5Nb₂O₆ (SBN50) ceramics were fabricated by solid-state ceramic route. The effects of CBS glass addition on the firing, the phase formation, the microstructure and dielectric characterization of SBN50 ceramics were investigated. Results show that the density of the samples firstly increase and then slightly decrease with increasing CBS glass content and the highest density achieved has been 97% of the theoretical density for the sample with 2% (mass fraction) CBS glass. The sintering temperature was significantly reduced from 1,350 to 1,100 °C. X-ray diffraction analysis shows the single phase tungsten bronze type structure is preserved up to 2% CBS glass. However, the samples with more than 5% CBS glass are found to have a secondary phase CaNbO₃. The diffuse character and the dielectric constant at room temperature increase as CBS glass content increases. The dielectric constant of the samples at the Curie temperature (T _c) firstly increases and then decreases with increasing the content of CSB glass. Interestingly, the grain sizes of SBN phase are found to obviously increase with increase in CBS glass doping level.     

The enhancement of relaxation of 0.5PZN-0.5PZT annealed in different atmospheres

The as-sintered Pb(Zn_1/3Nb_2/3)_0.5(Zr_0.47Ti_0.53)_0.5O₃ samples were annealed in oxygen and nitrogen. Both annealed specimens exhibited improved degree of relaxation compared with as-sintered specimens. However, the mechanisms inducing enhancement of relaxation were different in the two kinds of specimens. For the oxygen annealed sample, oxygen vacancies were partially filled, which induced the macro-microdomain transition and resulted in the increase of relaxation degree. Whereas, for the nitrogen annealed specimen, the emergence of pyrochlore phase was inevitable due to the flowing reductive atmosphere, the pyrochlore phase broke the long-range transition invariance of perovskite structure and played a key role in improving the relaxation.     

Compositional effects on the properties of (1-x)BaTiO3-xBi0.5Na0.5TiO3 ceramics

The compositional effects on the crystal structure, phase transition, dielectric, ferroelectric and piezoelectric properties of the (1-x)BaTiO₃-x(Bi_0.5Na_0.5)TiO₃ solid solution ceramics were investigated. After sintering at 1200 °C for 2 h, the ceramics with different content of (Bi_0.5Na_0.5)TiO₃ (BNT) formed single-phase solid solutions with perovskite structure. The lattice constant c/a ratio of the solid solutions decreased as BNT content increased except that with 20 mol% BNT, which had the largest value of c/a ratio for all samples. The second phase transition corresponding to BaTiO₃ (BT) at about 5 °C shifted to low temperature and gradually disappeared as BNT increased. A new secondary phase transition appeared at 32 °C and 64 °C, respectively, when BNT content was 5 and 14 mol%. The Curie temperature, T _c, shifted in the temperature range between 112 °C and 166 °C, and the remanent polarization, P _r, decreased whereas the coercive field, E _c, increased as the BNT content increased. The relatively high value of piezoelectric coefficient d₃₃ together with a relatively high Curie temperature and low loss tangent and stable dielectric properties were obtained when the addition of BNT was 20 mol%.     

Neutron structural study of the Bi-monolayer compound (Bi0.5Cu0.5)Sr2(Y0.8Cu0.2)Cu2O7 + δ—the Role of excess oxygen in superconductivity

Comparative neutron structural investigations are made on nonsuperconducting (slow-cooled) and superconducting (liquid-nitrogen quenched;T _c ^onset=70 K andR=0 at 20 K) samples of (Bi_0.5Cu_0.5)Sr₂(Y_0.8Cu_0.2)Cu₂O_{7 + δ} in order to examine the role of excess oxygen on the superconducting behavior of this “1212”-phase compound. Analysis of refined structural parameters shows that the two main factors which influence the superconductivity in (Bi, Cu)-1212 are: (i) the extent of occupancy of excess oxygen at O(5), the 2(e) site located in between the two CuO₂ pyramidal layers, and (ii) the length of the apical Cu(2)-O(2) bond. The (Bi, Cu)-O monolayer plays the role of the “charge reservoir” quite effectively as reflected by the substantial increase in the length of the apical (bridging) Cu(2)-O(2) bond due to depletion of excess oxygen in this layer. Surprisingly, vacancies at as many as 10% of the O(1) site belonging to the CuO₂ planes do not appear to disrupt the flow of current in the Cu(3d)-O(2p) planar network in the superconducting state. Relevant features of the structure of the (Bi, Cu)-1212 phase, in particular the role of excess oxygen and its occupancy at different sites, are discussed in the light of the available data on the isostructural (Pb, Cu)-1212 phase and the (La, Sr, Ca)₃-Cu₂O_{6 + δ} phase superconductors.     

Ion Beam Analysis and Electrical Resistivity Studies of (Cu0.5Tl0.5)-1223 Phase with Added Nano-oxides

In this study, superconducting samples of type Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10??? added by SnO₂ and In₂O₃ in nano-scale were prepared by a solid-state reaction technique. The concentrations of both SnO₂ and In₂O₃ were 0.0, 0.1, 0.2, 0.4, 0.6 and 1.0?wt% of the sample??s total mass. The prepared samples were characterized using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) for phase analysis and microstructure examination. The elemental content of the prepared samples was determined using energy dispersive X-ray (EDX) and particle induced X-ray emission (PIXE). The results of elemental content, determined from EDX and PIXE, were compared and discussed. In addition, The oxygen content of these samples was obtained using non Rutherford backscattering spectroscopy (RBS) at 3 MeV proton beam. It was found that the Oxygen-content of (Cu_0.5Tl_0.5)-1223 phase was not affected by both SnO₂ and In₂O₃ nano-oxides addition. The electrical resistivity of the prepared samples was measured by the conventional four-probe technique from room temperature down to the zero superconducting transition temperature (T ₀). An increase in the superconducting transition temperature T _c from 106 to 119 K was observed as x was varied from 0.0 to 0.6?wt% for (SnO₂) _x Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10??? , followed by a systematic decrease with increasing nano-SnO₂ addition. On the other hand, the T _c values for (In₂O₃) _x Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10??? show a small variation with?x. Moreover, the variation rate of T _c with x, for both nano-additions, was found to be directly proportional to the variation of the volume fraction of the prepared samples.     

Oxygen release behavior of metastable tetragonal t′meta-(Ce0.5Zr0.5)2 phases prepared by reduction and successive oxidation of t′ phase

Tetragonal CaF₂-related-type t′-/Ce_0.5Zr_0.5)O₂ phase was reduced at 773 K ≤ T_red. ≤ 1073 K to prepare precursors with various oxygen compositions: Ce₂Zr₂O_712d /0.111 < δ < 0.379). Metastable tetragonal t^′_meta-(Ce_0.5Zr_0.5)O₂ phases were prepared by oxidizing in O₂ at 873 K the precursors, and subjected to evolved oxygen gas analysis by heating the samples at a constant rate. When the precursor was prepared at T_red: ? 773 K; i.e. δ ? 0:379; the oxygen release behavior of the tetragonal phase agreed approximately with that of the t^′. For δ < 0.29, distinct features of the t^′_meta-(Ce_0.5Zr_0.5)O₂ appeared in the XRD results and Raman spectra. The temperature exhibiting the maximum release rate of oxygen from the t^′_meta became lower with decreasing the d value. It could be concluded that the thermodynamic behavior of the t^′_meta is related closely to the precursor composition and becomes more unstable with decrease in the δ value. The t^′ and t^′_meta phases with disordered arrangement of Ce and Zr ions may belong to the same space group; nevertheless, difference in the random arrays of the Ce and Zr ions was suggested on the basis of the present experimental results.     

Structure of B6O boron-suboxide by Rietveld refinement

The structures of the B₆O samples prepared by oxidizing boron with ZnO at temperatures of 1350–1500°C in an argon atmosphere have been refined by the Rietveld method. The B₆O samples were found to contain an amorphous phase from their X-ray diffraction profiles in addition to B₆O diffraction peaks. The results indicate that the B₆O samples, space group R¯3m, no.166, a _hex = 0.5367(1) nm and c _hex = 1.2328(2) nm in the hexagonal unit cell, have oxygen deficiencies with 0.76(6) oxygen occupancy. A radial distribution function method applied to an extracted portion of the amorphous phase, suggests that each amorphous phase has nearly similar short-range order structure to that of the -tetragonal boron type rather than to those of any other related boron phases.     

Top-Seeded Melt-Growth of YBa2Cus3Ox Crystals for Neutron Diffraction Studies

We have grown cubic centimeter-size crystals of YBa₂Cu₃O _x suitable for neutron studies, by a top-seeded melt-growth technique. Growth conditions were optimized with an eye toward maximizing phase purity. It was found that the addition of 2% Y₂BaCuO₅ and 0.5% Pt (by mass) were required to prevent melt loss and to obtain the highest crystallinity. A neutron diffraction study on a mosaic of six such crystals found that the final Y₂BaCuO₅ concentration was 5%, while other impurity phases comprised less than 1% by volume. The oxygen content was set to x = 6.5, the crystals were detwinned, and then carefully annealed to give the well-ordered ortho-II phase. The neutron study determined that 70% of the mosaic's volume was in the majority orthorhomic domain. The neutron (006) and (110) rocking curve widths were 1° per crystal and 2.2° for the mosaic, and the oxygen chain correlation lengths were >100 Å in the a- and b-directions and 50 Å in the c-direction.     

Effect of Ba Substitution on the Superconducting Properties and the Irreversibility Line of the Compounds TIPb 1223: Tl0.5Pb0.5(Sr 2−xBax)Ca2Cu3O9−δ

The superconducting properties and the irreversibility line of the Tl_0.5Pb_0.5(Sr_2?xBa_x)Ca₂Cu₃O_9?δ were studied by ac susceptibility on both ceramic and powdered samples. The samples were prepared by solid state reaction in flowing oxygen at 880°C or in sealed quartz tube at 960°C. The irreversibility lines were measured up to 4 Tesla and were determined by the maximum of the X″ peak, using the same ac field to allow comparison between them. The presence of the 1212 phase as a minor superconducting phase was clearly evidenced in all cases. The case of samples of TlPbl223 with Tl/Pb ratio different from unity was also examined.     

Mechanical and Electrical Properties of (Cu0.5Tl0.5)-1223 Phase Added with Nano-Fe2O3

Superconducting samples of type (Cu_0.5Tl_0.5)-1223 added with nano-Fe₂O₃ (x=0.0, 0.1, 0.2, 0.4, 0.6 and 1.0 wt.%) were prepared by solid-state reaction technique. The prepared samples were characterized using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) for phase analysis and microstructure examination. The elemental content of the prepared samples was determined using particle induced X-ray emission (PIXE), whereas the Oxygen-content of these samples was obtained using non Rutherford backscattering spectroscopy at 3 MeV proton beam. It was found that the Oxygen-content of (Cu_0.5Tl_0.5)-1223 phase was not affected with the addition of nano-Fe₂O₃. The electrical resistivity measurements showed that the superconducting transition temperature (T _c ) increases up to x=0.2 wt.%, followed by a systematic decrease for x>0.2 wt.%. In addition, room temperature Vickers microhardness (H _v ) measurements were carried out at different applied loads (0.49–2.94 N) to study the performance of the mechanical properties of samples. The experimental results of H _v were analyzed using different models such as elastic, energy dissipation, energy balance and modified energy balance models. It has been found that the energy dissipation model is in a good agreement with the microhardness data.     

X-ray Diffraction Study of the Structure and Defect System of Yb-Activated (Na0.5Gd0.5)WO4 Crystals

Nominally pure and Yb-activated Czochralski-grown (Na_0.5Gd_0.5)WO₄ crystals (scheelite type) were studied by x-ray diffraction (phase analysis, unit-cell parameters, and structure refinement by the Rietveld method and single-crystal techniques). A pseudotetragonal (orthorhombic) superstructure was revealed, which was shown to have doubled unit-cell parameters compared to the scheelite cell. Some of the crystals were found to contain tungsten and oxygen vacancies, which give rise to additional optical absorption. The effects of the growth and heat-treatment conditions and Yb activation on the structure, defect system, and additional absorption spectrum of (Na_0.5Gd_0.5)WO₄ are analyzed.     

Effect of oxygen concentration on superconductivity of Bi-Sr-Ca-K-Cu-O compounds

In order to study the relation between the oxygen content and superconductivity samples of Bi₂Sr₂Ca_1–x K _x Cu₂O _y (x=0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0) were prepared and treated under different conditions. It was found that the superconducting properties are sensitive to the oxygen concentration and theT _c,zero of Bi₂Sr₂Ca_1–x K _x Cu₂O _y can be shifted over a range of about 22 K by the changing oxygen concentration; no structural difference induced by oxygen were observed. The change in superconducting properties may be the result of a change in Cu average valence state. In addition, the change in superconducting phase with K⁺ concentration is also studied.     

Enhanced dielectric temperature stability and energy-storage properties of (Y0.5Nb0.5)4+ co-doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free relaxor ceramics

(Bi_0.5Na_0.5)_0.94Ba_0.06Ti_1?x(Y_0.5Nb_0.5)_xO₃ (abbreviated as BNTBT-100xYN) lead-free relaxor ceramics were designed and prepared using a traditional solid-state sintering technique. The influences of the introduction of (Y_0.5Nb_0.5)⁴⁺ complex ions for the dielectric properties and energy storage performances of BNTBT-100xYN ceramics were systematically studied. All samples exhibited a typical pseudo-cubic symmetry structure and obtained the dense microstructure with the uniform distribution of all elements. The ergodic relaxor behavior of all ceramics was observed and revealed a trend of increase as a function of composition. It accelerated the improvement of the temperature stability of the dielectric constant. All samples showed a single grain conduction mechanism and the activation energy decreased with the addition of composition. It is related to the generation of oxygen vacancies induced by the defect dipoles. BNTBT-6YN ceramic revealed excellent dielectric temperature stability within the temperature range from 87 to 479 °C and the loss tangent less than 0.05 between 25 °C and 474 °C. Besides, a high recoverable energy density of?~?0.91 J/cm³ with the corresponding efficiency of?~?78.5% at applied 115 kV/cm field was achieved for BNTBT-5YN ceramic. Hence, BNTBT-5YN and BNTBT-6YN ceramics will become one of the outstanding dielectric ceramics for the electronic components.

     

Synthesis of monophasic Ce<Subscript>0.5</Subscript>Zr<Subscript>0.5</Subscript>O<Subscript>2</Subscript> solid solution by microwave-induced combustion method

Nanocrystalline monophasic Ce_0.5Zr_0.5O₂ solid solution (1:1 molar ratio) has been synthesized by microwave-induced combustion method in a modified domestic microwave oven (2.45 GHz, 700 W) in approximately 40 min from cerium nitrate and zirconium nitrate precursors using urea as ignition fuel. For the purpose of better comparison, a Ce _x Zr_{1 − x} O₂ solid solution (1:1 molar ratio) was also synthesized by a conventional co-precipitation method from nitrate precursors and subjected to different calcination temperatures. The synthesized powders of both methods were characterized by means of X-ray powder diffraction, thermogravimetry/differential thermal analysis, scanning electron microscopy, and BET surface area techniques. Oxygen storage capacity (OSC) measurements were performed to understand the usefulness of these materials for various applications. The characterization results reveal that the sample obtained by microwave-induced combustion-synthesis route exhibits homogeneous monophasic Ce_0.5Zr_0.5O₂ solid solution whereas the co-precipitated sample displays compositional heterogeneity. The OSC measurements reveal that the materials synthesized by both methods exhibit comparable oxygen vacancy content (δ).     

Structural Studies of the Superconducting La2.5Y0.5CaBa3(Cu1?xFex)7Oz (0 ≤ x ≤ 0.1) Perovskite System by Neutron Diffraction

We have investigated the effect of Fe substitution on the structural and superconducting properties of La_2.5Y_0.5CaBa₃(Cu_1–x Fe _x )₇O _z system by Rietveld refinement of the neutron diffraction patterns of three samples with x = 0.02 (labelled B₁), x = 0.06 (B₂), and x = 0.10 (B₃) along with X-ray diffraction, resistivity, AC susceptibility, and oxygen-content measurements. Samples B₁, B₂, and B₃ are superconducting with T _c ^R=0 values of 73, 62, and 41 K, respectively. Neutron diffraction studies confirm (i) the formation of a single phase tetragonal structure (space group P4/mmm) for all three samples, (ii) Ca and Y ions substitution at the La site concomitantly displaces La onto Ba sites, and (iii) increasing x from 0.02 to 0.10 increases oxygen content (the amount of oxygen per unit cell), as well as Cu(1)— O(4) and Cu(1)— O(1) bond lengths whereas Cu(2)— O(4) bond length decreases with corresponding decrease in T _c to 41 K due to increasing occupancy of Fe ions at Cu(2) site. The change in bond lengths with oxygen content are essentially the same as those of Fe content (x). Present studies establish a correlation between the bond lengths (Cu(1)— O(1), Cu(1)— O(4), and Cu(2)— O(4)) and the measured T _c values of three samples.     

X-Ray Diffraction Studies on LaBa2Cu3Ox Cuprates with Iron Substitution

LaBa₂Cu_3–y Fe _y O _x ceramic samples with y = 0.00–1.50 are synthesized by the solid-state reaction technique. Rietveld analysis for X-ray diffraction is performed on these iron-doped samples. A BaCuO₂ impurity phase and a ceramic cuprate phase coexist in each sample. An orthorhombic-to-tetragonal (OT) phase transition occurs in the doping range of 0.03y0.06, and a tetragonal-to-orthorhombic (TO) one occurs in the doping level of 0.10y0.25. There is a jump in the structural parameters due to the iron doping. The occupancy of oxygen at the O(4) site, which is in the La plane at z = 1/2, increases with increase in iron content. These results may relate to the iron preferential occupancy for the Cu(1) site at the lower doping level, and for Cu(2) sites at the higher doping level.     

Cellulose-precursor synthesis of nanocrystalline Co0.5Cu0.5Fe2O4 spinel ferrites

Nanocrystalline Cu_0.5Co_0.5Fe₂O₄ powders were prepared via a metal-cellulose precursor synthetic route. Cellulose was used as a fuel and a dispersing agent. The resulting precursors were calcined in the temperature range of 450–600 °C. The phase development of the samples was determined by using Fourier transform infrared (FT-IR) spectroscopy and powder X-ray diffraction (XRD). The field-dependent magnetizations of the nanopowders were measured by vibrating sample magnetometer (VSM). All XRD patterns are of a spinel ferrite with cubic symmetry. Microstructure of the ferrites showed irregular shapes and uniform particles with agglomeration. From XRD data, the crystallite sizes are in range of 16–42 nm. Saturation magnetization and coercivity increased with increasing calcining temperature due to enhancement of crystallinity and reduction of oxygen vacancies.     

Role of La0.5Sr0.5CoO3 template layers on dielectric and electrical properties of pulsed-laser ablated Pb(Nb2/3Mg1/3)O3-PbTiO3 thin films

Relaxor ferroelectric thin films of 0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ (PMN-PT) deposited on platinized silicon substrates with and without template layers were studied. Perovskite phase (80% by volume) was obtained through proper selection of the processing conditions on bare Pt/Ti/SiO₂/Si substrates. The films were initially grown at 300 °C using pulsed-laser ablation and subsequently annealed in a rapid thermal annealing furnace in the temperature range of 750-850 °C to induce crystallization. Comparison of microstructure of the films annealed at different temperatures showed change in perovskite phase formation and grain size etc. Results from compositional analysis of the films revealed that the films initially possessed high content of lead percentage, which subsequently decreased after annealing at temperature 750-850 °C. Films with highest perovskite content were found to form at 820-840 °C on Pt substrates where the Pb content was near stoichiometric. Further improvement in the formation of perovskite PMN-PT phase was obtained by using buffer layers of La_0.5Sr_0.5CoO₃ (LSCO) on the Pt substrate. This resulted 100% perovskite phase formation in the films deposited at 650 °C. Dielectric studies on the PMN-PT films with LSCO template layers showed high values of relative dielectric constant (3800) with a loss factor (tan δ) of 0.035 at a frequency of 1 kHz at room temperature.     

Effect of the level of the addition of Pb(Y0.5Nb0.5)O3 on the structure, microstructure and ferroelectric properties of PZT(53/47)

In this work an attempt is made to study [Pb(Zr_0.53Ti_0.47O₃)O₃]_1-X-[Pb(Y_0.5Nb_0.5)O₃]_X system with x = 0.0125, 0.025, 0.05, 0.075 and 0.1. It was shown that there is limited solid solubility (2.5 mol%) of Pb(Y_0.5Nb_0.5)O₃ (PYN) in PZT (53/47). The substitution of PYN gave rise to the reduction of the volume of PZT’s unit cell. For the samples doped above this level of PYN, an extra phase comprising of Y³⁺, Zr⁴⁺ and Ti⁴⁺ cations were detected based on EDS-SEM and XRD analysis and also a structural shift towards a rhombohedral phase was noticed for the main PZT phase. Further, the addition of PYN up to 2.5 mol% was seen to increase the room temperature relative permittivity and d₃₃ parameter. However, these parameters declined for the samples substituted with more than 2.5 mol% PYN due to the formation of non ferroelectric extra phase.