Magnetic properties of doped LaMnO<Subscript>3</Subscript> ceramics obtained by a polymerizable complex method

Substituted lanthanum manganites with the general formula A_1−x B _x MnO₃ (A = La, B = Ca, Sr…) have attracted a lot of attention due to their exceptional electric and magnetic properties. In this work, pure and Ca²⁺, Sr²⁺-doped LaMnO₃ (LMO) with the concentrations of dopants 30% Ca²⁺ (LCMO), 30% Sr²⁺ (LSMO) and 15% Ca²⁺ + 15% Sr²⁺ (LCSMO) (in mol. %) were synthesized by polymerizable complex method. Bulk samples were prepared by sintering at 1300 °C for 4 h in oxygen atmosphere. It was found that sintering in oxygen atmosphere enables preparation of single phase ceramics with rhombohedral crystal structure. Chemically prepared fine, submicronic precursor powders provided uniform microstructure and grain size distribution in final ceramics. As a result, pure and doped LMO ceramics with excellent microstructural and magnetic properties were obtained. Depending on the composition, magnetic measurements showed high saturation magnetizations (up to 93 emu/g), with values of the Curie temperature in the range 180–390 K and magnetoresistance up to 67%.     

Synthesis and microwave dielectric properties of Ca<Subscript>0.6</Subscript>La<Subscript>0.267</Subscript>TiO<Subscript>3</Subscript> nanocrystalline powders by sol–gel method

Ca_0.6La_0.267TiO₃ nanocrystalline powders were successfully synthesized by the sol–gel method using PEG1000 as a dispersant in this study. The sinterability of the powders and the microwave dielectric properties of the ceramics were also investigated. The XRD diffraction result showed that pure Ca_0.6La_0.267TiO₃ powder with orthorhombic perovskite structure could be synthesized at 600 °C for 2 h without any detectable intermediate phase. The average grain size of the as-synthesized powder was as low as 35 nm. Compared with Ca_0.6La_0.267TiO₃ ceramics fabricated by conventional solid-state process, the bulk materials prepared by sintering as-prepared nanopowders performed better in densification and microwave dielectric properties. The ceramics sintered at 1,300 °C exhibited a higher relative density of 98.3% combined with a dielectric constant (ε _r ) of 120.3, a quality factor (Q × f) of 23,550 GHz and a temperature coefficient of resonant frequency (τ _f ) of +220.7 ppm/°C, respectively.     

Preparation of Ca<Subscript>3</Subscript>Co<Subscript>4</Subscript>O<Subscript>9</Subscript> by polyacrylamide gel processing and its thermoelectric properties

Ca₃Co₄O₉ powder was prepared by a polyacrylamide gel route in this paper. The effect of the processing on microstructure and thermoelectric properties of Ca₃Co₄O₉ ceramics via spark plasma sintering were investigated. Electrical measurement shows that the Seebeck coefficient and conductivity are 170 μV/K and 128 S/cm, respectively, at 700 °C, yielding a power factor value of 3.70 × 10⁻⁴ W m⁻¹ K⁻² at 700 °C, which is larger than that of Ca₃Co₄O₉ ceramics via solid-state reaction processing. The polyacrylamide gel processing is a fast, cheap, reproducible and easily scaled up chemical route to improve the thermoelectric properties of Ca₃Co₄O₉ ceramics by preparing the homogeneous and pure Ca₃Co₄O₉ phase.     

B<Subscript>2</Subscript>O<Subscript>3</Subscript> additives on sintering and microwave dielectric behaviors of Mg<Subscript>4</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> ceramics synthesized through the aqueous sol–gel Process

The relationships between the sintering temperatures and the microwave dielectric properties of (1−x)Mg₄Nb₂O₉-xB₂O₃ (x = 0.5–10 wt. %) compounds were investigated by the sol–gel method in order to reduce the sintering temperature in this study. A suitable amount of B₂O₃ doping was effective in allowing low sintering temperatures without a little detrimental effect on these dielectric properties of the Mg₄Nb₂O₉ compounds. The variations in the dielectric constant (ε _r ) and the quality factor (Q·f) of the Mg₄Nb₂O₉ compounds depended on the amount of B₂O₃ doping and the sintering temperature. As a result, a ε _r value of ~12.8 and a Q·f value of ~142,570 GHz were obtained when the Mg₄Nb₂O₉ compound with x = 3% was sintered at 1,200 °C for 4 h. The temperature coefficient of resonant frequency (τ _f ) of the 3%-B₂O₃ doping Mg₄Nb₂O₉ compound slightly changed from −33 to −48 ppm/°C with an increased sintering temperature.     

Preparation of a biphasic calcium phosphate from Ca(H2PO4)2·H2O AND CaCO3

Sintered hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP) are the two most common bio-ceramics for bone substitute. Although their composition are analogous to the constituent of human hard tissue, but some disadvantages are always exist till now, such as they need a high temperature sintering process, and this would lose the functional groups for bioactivity and closed the micro- pores without any interconnections, that hamper the body fluid transportation and angiogenesis during regeneration. Furthermore, the sintered ceramics with block and fixed size is difficult to fit non-regular defect area. In this study, the mixtures of Ca(H₂PO₄)₂·H₂O and CaCO₃ were adjusted firstly, then distilled water were introduced in wet chemical method, and a biphasic ceramic of HAp/β-TCP will be obtained after drying and sintering, then the result product that prepared by wet chemical method will be the sample in this investigation. The physical properties of result powders were characterized by DTA/TG, XRD and SEM, respectively, the particle size of two bio-ceramics that after heat treatment were found under 5 μm in SEM examination. Powder type calcium phosphate ceramics with the Ca/P molar ratio of 1.67 can be as bone cement by mixing with polymeric binder, the fine particle product of the setting cement will possess micro-pores and macro-pores that after suitable heat treatment process, and this is good for fluid transportation and tissue regeneration.     

Preparation and Electrical Properties of Hydroxyapatite Containing Yttrium

Abstract

Hydroxyapatite (HAP) containing yttrium ion was synthesized and sintered for obtaining apatite ceramics with new functional properties. The preparation of the ceramics was carried out by synthesis using the wet process and by sintering under water vapor atmosphere. The product was recognized to be a solid solution. By substituting Y for Ca, O^2- and lattice defect (□) will form as follows: OH^? → O^2- + H₂O + □. Then, a following formula can be described for this solid solution produced:

Ca₁0-x^yx^(PO₄)2-x-2y^Ox+2y□y. The ionic conductivity of the product was measured by the ac two probe method. The plot.of conductivity-Y content relation gave a characteristic curve with a sharp peak at a fixed composition, Y=0.65. It was considered that this tendency was due to a change in the charge carrier in HAp crystal from OH- to H⁺ and O^2? with varying Y content. Electromotive force was observed in a water vapor cell assembled using the phosphate ceramics, and hydrogen gas generation was recognized. These phenomena led a fact that proton conduction exists in the ceramics. It was concluded that this ceramics will be used as a fuel cell.     

Neutron powder diffraction study and B-site ordering in microwave dielectric ceramics Ba(Ca1/3Nb2/3)O3

Microwave dielectric powder Ba(Ca_1/3Nb_2/3)O₃ with high B-site cation ordering was synthesized by the molten salt method. Neutron powder diffraction (NPD) and Raman scattering spectra were introduced to investigate the variable ordering degree during the sintering process. It was revealed that the as-synthesized Ba(Ca_1/3Nb_2/3)O₃ powder had a nearly completely ordered structure, and the sintered Ba(Ca_1/3Nb_2/3)O₃ presented a bit higher ordering degree based on the detailed quantitative NPD Rietveld full profile fitting. The complete Raman mode assignment for the Ba(Ca_1/3Nb_2/3)O₃ was presented. The phonon bands could also confirm the order–disorder structural model and increasing ordering degree with the increasing sintering temperature. Final microwave dielectric measurements on sintered samples showed the present compound to tailor other dielectric materials for microwave applications with the dielectric properties of ?_r = 47.11, and Qf = 1389 GHz, and τ_f was about 113 ppm/°C.     

Phase,crystal struture and sintering behavior of shock-synthesized Pb(Zr0.95Ti0.05)O3 powders

With a cylindrical shock-wave-loading technique, the single perovskite-phase Pb(Zr_0.95Ti_0.05)O₃ powders (PZT 95/5) were synthesized by shock-induced chemical reactions in heterogeneous multi-material powder mixtures of Pb₃O₄, ZrO₂ and TiO₂. The phase and crystal structure of as-synthesized powders were characterized by X-ray diffraction (XRD) and fourier transform infrared (FT-IR) analysis. And the microstructure and electrical properties of PZT 95/5 ceramics prepared with as-synthesized PZT powders at different sintering temperature were analyzed. The results showed that the shock-wave-induced a large quantity of lattice defects and distortion of the crystal structure in the shock-synthesized PZT powders, which could enhance the sintering activity. Thus, the optimal density and electrical properties of PZT ceramics prepared with as-synthesized powders could be obtained at a sintering temperature of 1200–1225 °C for 3 h, significantly lower than the sintering temperature of PZT 95/5 ceramics prepared by conventional solid-state reaction.     

Some studies on the phase formation and kinetics in TiO<Subscript>2</Subscript> containing lithium aluminum silicate glasses nucleated by P<Subscript>2</Subscript>O<Subscript>5</Subscript>

Lithium aluminum silicate (LAS) glasses of compositions (wt%) 10.6Li₂O–71.7SiO₂–7.1Al₂O₃–4.9K₂O–3.2B₂O₃–1.25P₂O₅–1.25TiO₂ were prepared by the melt quench technique. Crystallization kinetics was investigated by the method of Kissinger and Augis–Bennett using differential thermal analysis (DTA). Based on the DTA data, glass ceramics were prepared by single-, two-, and three-step heat treatment schedules. The interdependence of different phases formed, microstructure, thermal expansion coefficient (TEC) and microhardness (MH) was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo-mechanical analysis (TMA), and microhardness (MH) measurements. Crystallization kinetics revealed that Li₂SiO₃ is the kinetically favored phase with activation energy of 91.10 kJ/mol. An Avrami exponent of n = 3.33 indicated the dominance of bulk crystallization. Based upon the formation of phases, it was observed that the two-stage heat treatment results in highest TEC glass ceramics. The single-step heat treatment yielded glass ceramics with the highest MH.     

Thermal investigations on phase transformations of Syrian phosphorite: Part I

The phase transformations of Syrian phosphorite upon mechanochemical activation are examined in the present work. The latter is carried out in planetary mill equipped with 20 mm steel milling bodies and duration from 30 to 300 min. The established by means of DTA, DTG, TG analyses transformation of non-activated carbonate fluorine apatite type B into the carbonate hydroxyl fluorine apatite (COHFAp) mixed type A2-B leads to substantial changes in the properties of the activated samples expressed in lowering the degree of crystallinity, strong defectiveness of the structure, and increase of the citric solubility. The thermal analysis gives evidence for the decomposition of the carbonate-containing component within the phosphorite, as from the positions placed in the vicinity of the hexagonal 6₃ axis (type A2), as well as from the positions of the phosphate ion (type B), and from the free carbonates. The data from the thermal analysis, the powder X-ray analysis and the infrared spectroscopy give also evidence for phase transformations of the activated apatite (with admixtures of quartz and calcite) into Ca₁₀FOH(PO₄)₆, β-Ca₃(PO₄)₂, Ca₄P₂O₉, Ca₃(PO₄)₂ · Ca₂SiO₄ and for that one of the quartz—into larnite and wollastonite. The influence of the α-quartz as a concomitant mineral is considered to be positive. The α-quartz forms Si–O–Si–OH bonds retaining humidity in the solid phase thus facilitating the isomorphous substitution OH⁻ → F⁻ with the subsequent formation of partially substituted COHFAp. Calcium silicophosphate and Ca₄P₂O₉ are obtained upon its further heating. The presented here results settle a perspective route for processing of low-grade phosphate raw materials by means of tribothermal treatment aiming at preparation of condensed phosphates suitable for application as slowly acting fertilizer components.     

Thermal properties of Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–PbO–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glass system

Thermal behavior of xGa₂O₃–(50 − x)PbO–50P₂O₅ (x = 0, 10, 20, and 30 mol.% Ga₂O₃) and xGa₂O₃–(70 − x)PbO–30P₂O₅ (x = 0, 10, 20, 30, and 40 mol.% Ga₂O₃) glassy materials were studied by thermo-mechanical analysis (TMA) and differential thermal analysis (DTA). Replacement of PbO for Ga₂O₃ is accompanied by increasing glass-transition temperature (263 ≤ T _g/°C ≤ 535), deformation temperature (363 ≤ T _d/°C ≤ 672), crystallization temperature (396 ≤ T _c/°C ≤ 640) and decreasing of coefficient of thermal expansion (5.1 ≤ CTE/ppm K⁻¹ ≤ 16.7). Values of Hruby parameter were determined (0.1 ≤ K _H ≤ 1.3). The thermal stability of prepared glasses increases with increasing of concentration of Ga₂O₃.     

One-step approach for nano-crystalline hydroxyapatite coating on titanium via micro-arc oxidation

Nano-crystalline hydroxyapatite (HAp) films were formed at the surface of Ti by a single-step micro-arc oxidation (MAO) using Ca²⁺ and P⁵⁺ ion-containing electrolytes. The HAp films were 10–25 μm thick, showing strong crystallinity dependence on the CaCl₂ concentration in the electrolytes. Also, the formation of an amorphous CaTiO₃ interlayer was identified to exist between the HAp and Ti substrates. In contrast to the previous researches using K₂HPO₄ for the electrolytes, KH₂PO₄ was used in this study, and this could allow the formation of the crystalline HAp layer. It is suggested as the most probable mechanism for the HAp formation that the high-density hydroxyl groups of TiO(OH)₂, formed by the reactions between the amorphous CaTiO₃ interlayer and the H⁺ ions from the dissolution of the KH₂PO₄, can play a key role in the nucleation and crystal growth of HAp by attracting Ca²⁺ and P⁵⁺ ions in the electrolytes.     

Structure of the calcium pyrophosphate monohydrate phase (Ca2P2O7·H2O): towards understanding the dehydration process in calcium pyrophosphate hydrates

Calcium pyrophosphate hydrate (CPP, Ca₂P₂O₇·nH₂O) and calcium orthophosphate compounds (including apatite, octacalcium phosphate etc.) are among the most prevalent pathological calcifications in joints. Even though only two dihydrated forms of CPP (CPPD) have been detected in vivo (monoclinic and triclinic CPPD), investigations of other hydrated forms such as tetrahydrated or amorphous CPP are relevant to a further understanding of the physicochemistry of those phases of biological interest. The synthesis of single crystals of calcium pyrophosphate monohydrate (CPPM; Ca₂P₂O₇·H₂O) by diffusion in silica gel at ambient temperature and the structural analysis of this phase are reported in this paper. Complementarily, data from synchrotron X‐ray diffraction on a CPPM powder sample have been fitted to the crystal parameters. Finally, the relationship between the resolved structure for the CPPM phase and the structure of the tetrahydrated calcium pyrophosphate β phase (CPPT‐β) is discussed.     

A novel low temperature synthesis technique of sol–gel derived nanocrystalline alumina abrasive

The effect of ball milling process, co-doped seed and two step sintering technique on the properties of sol–gel derived alumina abrasive sintered at low temperature was investigated. The results showed that ball milling time with 10 h can be effective in enhancing the activity of the precursor and the microstructural uniformity of sintered alumina abrasive. A small amount of Al₂O₃–(NH₄)₃AlF₆ co-doped seed addition had potential synergistic effects for reducing α-Al₂O₃ phase transformation temperature and improving the mechanical property of alumina abrasive. A remarkable suppression of grain growth was achieved by controlling sintering temperature with two-step sintering method. Therefore, by using ball milling process, co-doping α-Al₂O₃–(NH₄)₃AlF₆ seed and two-step sintering technique, the sol–gel derived uniform nanocrystalline alumina abrasive is easily achieved at low temperature. Nanocrystalline alumina abrasive prepared at these conditions exhibited excellent mechanical properties and wear resistance compared to fused corundum abrasive and those sol–gel derived corundum abrasive with conventional sintering methods.     

Low temperature preparation and electric properties of highly (100)-oriented Pb<Subscript>0.8</Subscript> La<Subscript>0.1</Subscript>Ca<Subscript>0.1</Subscript>Ti<Subscript>0.975</Subscript>O<Subscript>3</Subscript> thin films prepared by a sol–gel route

Highly (100)-oriented Pb_0.8La_0.1Ca_0.1Ti_0.975O₃ (PLCT) thin films deposited on Pt/Ti/SiO₂/Si substrate were successfully achieved by a sol–gel route. The influence of annealing temperature on microstructures and electric properties was investigated; it was found that the PLCT film could be crystallized only at 450 °C. When the annealing temperature increased to 500 °C, the PLCT film exhibited highly (100)-oriented, which also possessed higher remnant polarization Pr (27 μC/cm²) and better pyroelectric figure of merit (F _d = 205 μC/m²k) at room temperature. It was also found too high annealing temperature (625 °C) could lead to recrystallization of film, and the small grains caused by recrystallization could make polarization reversal difficult and disturbed the preferred crystal growth in film, which was not benefit to obtain enhanced electric properties.     

Effect of vapor thermolysis on microstructure development of sol–gel-derived lead zirconate–titanate (PZT) and PZT-Sr(K<Subscript>0.25</Subscript>Nb<Subscript>0.75</Subscript>)O<Subscript>3</Subscript> solid solutions

Ceramic granules of PZT (Pb(Zr₅₃,Ti₄₇)O₃) and fibers of SKN-doped PZT (1 Mol-% Sr(K_0.25Nb_0.75)O₃ substitution in PZT) were fabricated from sol–gel precursors. The transformation of the metal–organic gel to the oxide and its crystallization behavior was investigated by thermogravitmetry, and XRD. The formation of pyrochlore or perovskite phase was sensitive to the preceeding heat treatment conditions in moist atmosphere (termed vapor thermolysis). Lower thermolysis temperatures resulted in the preferred formation of metastable pyrochlore phase. Higher thermolysis temperatures favored the formation of perovskite. Investigation of sintered materials revealed a superior sintering activity for samples with pronounced intermediate pyrochlore content whereas low-pyrochlore samples remained highly porous after sintering. For constant chemical precursors the vapour thermolysis conditions (220–280 °C) siginificantly affected crystallization and sintering behavior of the PZT and SKN-PZT material.     

Crystal chemistry and phase equilibria of the CaO-½Eu2O3-CoOz system at 885 °C

The CaO-½Eu₂O₃-CoO_z system prepared at 885 °C in air consists of two calcium cobaltate compounds, namely, the 2D thermoelectric oxide solid solution, (Ca_3−xEu_x)Co₄O_9−z (0 ≤ x ≤ 0.5) which has a misfit layered structure, and the 1D Ca₃Co₂O₆ compound which consists of chains of alternating CoO₆ trigonal prisms and CoO₆ octahedra. Ca₃Co₂O₆ was found to be a point compound without the substitution of Eu on the Ca site when prepared at 885 °C. A solid solution region of distorted perovskite, (Eu_1−xCa_x)CoO_3−z (0 ≤ x ≤ 0.22, space group Pnma) was established. The (Eu_0.91(1)Ca_0.09(1))CoO_3−z perovskite member has a distorted structure with tilt angles θ (17.37°), ϕ (8.20°), and ω (19.16°) which represent rotations of an octahedron about the pseudo-cubic perovskite [110]_p, [001]_p and [111]_p axes. The reported Eu₂CoO₄ phase was not observed at 885 °C, but a ternary Ca-doped oxide, (Eu_1+xCa_1−x)CoO_4−z (Bmab) where 0 ≤ x ≤ 0.10 was found to be stable at this temperature. In the peripheral binary systems, Eu was not present in the Ca site of CaO, while a small solid solution region was identified for (Eu_1−xCa_x)O_(3−z)/2 (0 ≤ x ≤ 0.05). Seven solid solution tie-line regions and six three-phase regions were determined in the CaO-½Eu₂O₃-CoO_z system in air.     

Indium oxide co-doped with tin and zinc: A simple route to highly conducting high density targets for TCO thin-film fabrication

Indium oxide co-doped with tin and zinc (ITZO) ceramics have been successfully prepared by direct sintering of the powders mixture at 1300 °C. This allowed us to easily fabricate large highly dense target suitable for sputtering transparent conducting oxide (TCO) films, without using any cold or hot pressing techniques. Hence, the optimized ITZO ceramic reaches a high relative bulk density (∼ 92% of In₂O₃ theoretical density) and higher than the well-known indium oxide doped with tin (ITO) prepared under similar conditions. All X-ray diagrams obtained for ITZO ceramics confirms a bixbyte structure typical for In₂O₃ only. This indicates a higher solubility limit of Sn and Zn when they are co-doped into In₂O₃ forming a solid-solution. A very low value of electrical resistivity is obtained for [In₂O₃:Sn_0.10]:Zn_0.10 (1.7 × 10⁻³ Ω cm, lower than ITO counterpart) which could be fabricated to high dense ceramic target suing pressure-less sintering.     

Development of sulfide glass-ceramic electrolytes for all-solid-state lithium rechargeable batteries

Development of Li₂S–P₂S₅-based glass-ceramic electrolytes is reviewed. Superionic crystals of Li₇P₃S₁₁ and Li_3.25P_0.95S₄ were precipitated from the Li₂S–P₂S₅ glasses at the selected compositions. These high temperature or metastable phases enhanced conductivity of glass ceramics up to over 10⁻³ S cm⁻¹ at room temperature. The original (or mother) glass electrolytes itself showed somewhat lower conductivity of 10⁻⁴ S cm⁻¹ and have important role as a precursor for obtaining the superionic crystals, which were not synthesized by a conventional solid-state reaction. The substitution of P₂O₅ for P₂S₅ at the composition 70Li₂S·30P₂S₅ (mol%) improved both conductivity and electrochemical stability of glass-ceramic electrolytes. The all-solid-state In/LiCoO₂ cell using the 70Li₂S·27P₂S₅·3P₂O₅ (mol%) glass-ceramic electrolyte showed initial capacity of 105 mAh g⁻¹ (gram of LiCoO₂) at the current density of 0.13 mA cm⁻² and exhibited higher electrochemical performance than that using the 70Li₂S·30P₂S₅ glass-ceramic electrolyte.     

Theoretical study of reaction mechanism for Se + O<Subscript>3</Subscript>

The reaction mechanism of Se + O₃ on the singlet potential energy has been investigated at CCSD(T)/6-311++G(2df,2pd) level of theory based on the geometric parameters optimized at the B3LYP/6-311++G(3df,3pd) level of theory. The calculated results show that the reactants are firstly associated into the adduct Se–O₃ with any intrinsic barrier. Subsequently, through a variety of transformations of isomer Se–O₃, two kinds of products P₁(SeO₃(D_3h)) and P₂(SeO + ³O₂) are obtained. The breakage and formation of the chemical bonds in the reaction have been studied by the topological analysis of electronic density. The topological analysis results show that the ring transitional structure region does not only occur in cis-OSeOO → SeO₃(C_s) process but also occur in SeO₃(C_s) → SeO₃(D_3h).