Effect of A (A = Li,Na, K) doping on structure and electrical properties of Mn1.2Ni0.3Co1.5O4 polycrystalline ceramics

Journal of Materials Science: Materials in Electronics - In this study, the alkali metal (Li/Na/K) doping has been achieved by using the sol–gel method, and the thermally sensitive ceramic...     

Effect of substrate on microstructure and mechanical properties of sol–gel prepared (K,Na)NbO3 thin films

Lead-free ferroelectric (K, Na)NbO₃ (KNN) thin films (～200 nm thickness) were prepared using a modified sol–gel method by mixing K and Na acetates with the Nb–tartarate complex, deposited by spin-coating method on Pt/Al₂O₃ and Pt/SiO₂/Si substrates and sintered at 650 °C. Pure perovskite phase of K_0.65Na_0.35NbO₃ in film on silicon were revealed, while film on alumina contained also small amount of secondary pyrochlore Na₂Nb₈O₂₁ phase. Homogenous microstructure of film on Si substrate was smoother with the lower roughness (～7.4 nm) and contained spherical (～50 nm) particles. The mechanical properties of films were characterized by nanoindentation. The modulus and hardness of KNN films were calculated from their composite values of film/substrate systems using discontinuous and modified Bhattacharya model, respectively. The KNN film modulus was higher on alumina substrate (91 GPa) in comparison with silicon substrate (71 GPa) and values of film hardness were the same (4.5 GPa) on both substrates.     

Continuous,martensitic nature of the transition ß→γ Li3PO4

The transformation Li₃PO₄ shows characteristics of both continuous and martensitic transformations. Below 340° C, no detectable transformation occurs; between 340 and 410° C, the transformation goes only partially to completion; above 410° C the transformation rapidly goes to completion. At any temperature in the range 340 to 410° C, transformation proceeds rapidly in the initial stages to attain a certain degree of transformation. With prolonged isothermal heating or grinding of the samples, further transformation does not occur. The reverse transformation could not be effected under normal, dry conditions.     

Effect of fine–grained structure on the mechanical properties of superalloys K3 and K4169

The fine–grained structures of superalloys K3 and K4169 were achieved by the addition of refiners. Test bars for the determination of mechanical properties were cast under the chosen conditions to study the tensile properties at room and intermediate temperatures, and the stress rupture properties at intermediate temperatures. Results show that for alloy K3, the yield and tensile strengths of the fine–grained samples are superior to those of the conventional ones at room and intermediate temperatures, but there is little difference in tensile plasticity. The stress rupture life of the fine–grained sample is much longer than that of the conventional at 750ºC, whereas it has no remarkable change at 800ºC. For alloy K4169, the yield and tensile strengths of fine–grained samples are still superior to those of the conventional ones at room temperature and 760ºC. In addition, the stress rupture life of the fine–grained sample is 1.1 times longer thanthat of the conventional one at 760ºC. However, the permanent plasticity almost remainsthe same. The fracture of the samples was examined by scanning electron microscopy (SEM) and the fracture mechanisms were investigated. © 2001 Published by Elsevier Science Ltd.     

Preparation and luminescence properties investigation of Eu3+, Tb3+-doped LaNbO4:RE3+ (RE = Eu,Eu/Tb,Tb)

Journal of Materials Science: Materials in Electronics - In this work, doped and co-doped LaNbO4:RE3+ (RE?=?Eu, Eu/Tb, Tb) single crystals were prepared by a unique hydrothermal method...     

Luminescence properties of the single-phase white light emitting phosphors Li0.04Ca0.93−xSiO3:Eu0.01,Bi0.02,Tbx

The single-phase white light emitting Li_0.04Ca_0.93?xSiO₃:Eu_0.01,Bi_0.02,Tb_x (x?=?0.01–0.05) phosphors were successfully synthesized using the sol–gel method. The phase structure, morphology and photoluminescence properties (PL) of phosphors were characterized by X-Ray Diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) and absorption spectra. The results show that the Li_0.04Ca_0.93?xSiO₃:Eu_0.01,Bi_0.02,Tb_x phosphors only consist of β-CaSiO₃ phase. The diffraction peak of (320) plane shows right-shift caused by Tb³⁺ ions doped into the β-CaSiO₃ host. The Li_0.04Ca_0.93?xSiO₃:Eu_0.01,Bi_0.02,Tb_x phosphors exhibit bright white emitting light on the excitation of 228 nm and the luminescence intensity increases with increase of Tb³⁺ ions until the concentration of Tb³⁺ ions is x?=?0.03. Then the luminescence intensity gradually decreases owing to concentration quenching behavior of Tb³⁺ ions. The emission color of phosphors would move from the white light region towards green direction with the increase of concentrations of Tb³⁺ ions. The color correlated temperature (CCT) values decrease from 8964 to 6118 K with the increase in concentration of Tb³⁺. Li_0.04Ca_0.9SiO₃:Eu_0.01,Bi_0.02,Tb_0.03 phosphor has higher band gap energy E_g (5.43 eV) than that of Li_0.04Ca_0.93SiO₃:Eu_0.01,Bi_0.02 phosphor. The addition of Tb³⁺ ions improve the thermal stability of phosphors with the thermal activation energy of 0.28 eV. The experimental result confirms that Tb³⁺ ions show the transfer energy behavior from Tb³⁺ to Eu³⁺ ions in the Li_0.04Ca_0.93?xSiO₃:Eu_0.01,Bi_0.02,Tb_x phosphors.

     

Effect of B2O3 on the densification and magnetic properties of Li–Zn ferrite

Densification, grain growth and magnetic properties of Li–Zn ferrite (Li_.30Zn_.4Fe_2.30O₄) doped with B₂O₃ as a sintering aid were investigated. B₂O₃ is a low melting point (460 °C) oxide and forms a liquid phase during sintering which affects the densification and grain growth of ferrites. Results showed that density and grain growth rate were sensitive to the B₂O₃ content and sintering temperature. At low amounts of B₂O₃ (<1 wt.%), an increase in the B₂O₃ content increased density and grain growth rate. The highest density and the maximum magnetization were obtained for the sample containing 1.0 wt.% B₂O₃ which was sintered at a lower temperature (1000 °C) for 1.5 h, in comparison with undoped samples. Higher B₂O₃ contents than 1.0 wt.% caused a decrease in density of samples due to secondary phases formation and evaporation of B₂O₃. The sample with the highest grain size showed the highest permeability and the lowest magnetic loss.     

Effect of fluoride on apatite formation from Ca4(PO4)2O in 0.1 mol L−1 KH2PO4

The effect of fluoride on the hydrolysis of tetracalcium phosphate (TTCP; Ca4(PO4)2O) was investigated in 0.1 mol l–1KH2PO4 containing 0–83 mol l–1 KF. Characterization of the final apatite phase formed by the hydrolysis was made with X-ray diffraction and SEM. The initial pH was between 4.5 and 5.4, depending on the solutions, and the pH rapidly increased and was kept constant between 7.3 and 6.5. An increase in KF concentration tended to lower the pH in the final stage of hydrolysis. The calcium concentration was considerably lower than the phosphorus concentration throughout the reaction. The fluoride concentration decreased shortly after the start of hydrolysis. The hydrolysis of TTCP in 0.1 mol l–1 KH2PO4 proceeded to form hydroxyapatite via DCPD when the KF concentration was low. The hydrolysis product was a calcium-deficient non-stoichiometric hydroxyapatite with a Ca/P ratio of about 1.5. With an increase in the KF concentration in the 0.1 mol l–1 KH2PO4 solution, TTCP directly transformed into hydroxyapatite containing F- ions or fluorapatite and with improved crystallinity. The addition of fluoride in the solution initially accelerated the formation of apatite. However, the layer of newly formed apatite adhering to the TTCP particles retarded TTCP dissolution; as a result, hydrolysis was delayed. IR analysis showed that the apatite phase contained HPO2–4 ions in the structure. The formula for the hydrolysis product of TTCP in the presence of fluoride can be expressed as follows: Ca10–x(HPO4)x(PO4)10–x(OH)2–x–yFy. © 1998 Chapman & Hall.     

Color tunning and temperature-dependent photoluminescence properties of Sr0.3Ca0.7−x−y(MoO4)2: xDy3+, yEu3+

Journal of Materials Science: Materials in Electronics - A series of Sr0.3Ca0.7?x?y(MoO4)2: xDy3+, yEu3+ phosphors with a tunable color was prepared by the conventional co-precipitation...     

Self-doping Effects on the Superconducting Properties of Cu0.5Tl0.25M0.25Ba2Ca2Cu3O10−δ (M = Bi, Hg, Nb, Pd, Li, Na, K)

The effect of self-doping and substitution of elements of higher and lower electronegativity, such as Bi, Hg, Nb, Pd, Li, Na, K, on the superconducting properties of Cu_0.5Tl_0.5−x M _x Ba₂Ca₂Cu₃O_10−δ with x=0.25 is investigated. These experiments demonstrated that the elements of lower electronegativity such as Li, Na, and K can easily liberate their outer most s-electron that could be supplied to the conducting CuO₂ planes of Cu_0.5Tl_0.5−x M _x Ba₂Ca₂Cu₃O_10−δ superconductor, and as a result, we get enhanced superconducting properties. However, highly electro-negative elements hinder the transfer of carriers from charge reservoir layer to the conducting CuO₂ planes and promote inferior superconducting properties. In the present studies, we have investigated the effect of post-annealing in nitrogen and oxygen atmospheres for optimizing the carriers in conducting CuO₂ planes of Cu_0.5Tl_0.5−x M _x Ba₂Ca₂Cu₃O_10−δ (M=Bi,Hg,Nb,Pd,Li,Na,K) superconductor. These studies are important since the density of carriers in the conducting CuO₂ planes determines the Fermi-vector k _F and Fermi velocity v _F of the carriers, which ultimately brings about the final superconducting state of the system.      

Effect of the addition of Ca2+ on the structure, microstructure and ferroelectric properties of (Pb1 − y Ca y )(Zr0.8Ti0.2)O3 system with y = 0.0, 0.02, 0.05 and 0.1

This work studies the relationship between ferroelectric properties and structural features of the (Pb_{1 – y} Ca _y )(Zr_0.8Ti_0.2)O₃ system with y = 0.0, 0.02, 0.05 and 0.1. All of the samples were prepared by hot-pressing of PZT calcined powder, prepared by conventional ceramic route. Single phase compositions of rhombohedral (RH) structure were observed for the whole series of the samples studied in this work. However, a linear decrease of RH lattice constant a _p is seen with increasing the Ca²⁺ concentration with a subsequent decrease of lattice strain expressed by (90 – _p). Further, a sharp decline is also observed in the magnitudes of saturation polarization (P _s) of the samples doped with 2 mol% Ca²⁺. However, the rate of decrease slows down for Ca²⁺ concentrations above this level. A diffuse phase transition was observed in the case of 10 mol% Ca²⁺-doped PZT(0.8) which is believed to be possibly due to the distribution in coupling strengths created from a random compositional fluctuations of Ca²⁺ and Pb^2– ions on A-sites. The results are interpreted on crystal-chemical grounds. It is proposed that the long range coupling of (Zr/Ti)O₆ coordination octahedra and Pb²⁺ ions, due to the covalency of the Pb–O bond, is interrupted by the incorporation of Ca²⁺. By considering the effect of calcium on coupling strength and coupling distribution, the observed dielectric response for the above compositions is qualitatively explained.     

Phase structure and electrical properties of (Li,Ta)-doped (K,Na)NbO<Subscript>3</Subscript> lead-free piezoceramics in the vicinity of Na/K = 50/50

The phase structure and electrical properties of (K,Na)NbO₃ (KNN)-based lead-free piezoelectric ceramics with nominal composition Li_0.03 (Na _x K_1−x )_0.97Nb_0.8Ta_0.2O₃ (LKNNT, x = 0.50−0.55) were investigated with an emphasis on the influence of Na/K ratio. By XRD and Raman measurements, it was revealed that the phase transition from the co-existence of O ₁ and T ₁ to the co-existence of O ₂ and T ₂ occurs when x = 0.52. At this Na/K ratio, a peak of dielectric constants was obtained, which also corresponds to a morphotropic phase boundary between T ₁ and T ₂ besides that between O ₁ and O ₂ in LKNNT ceramics. All the Li_0.03 (Na _x K_1−x )_0.97Nb_0.8Ta_0.2O₃ ceramics with x = 0.50 − 0.55 show excellent piezoelectric performance, and the piezoelectric coefficient d*₃₃ can reach as high as 335 pm/V. The room-temperature piezoelectric properties in the present LKNNT ceramics are not sensitive to the change of Na/K ratio, indicating that the orthorhombic to tetragonal phase co-existence dominates the enhancement of piezoelectric properties. However, the results on the piezoelectricity measurement at elevated temperature showed possible to further enhance piezoelectric properties by adjusting Na/K ratio in the tetragonal LKNNT ceramics.     

A novel Ca3(PO4)2–CaCO3 support mixture for the CVD synthesis of roughened MWCNT-carbon fibres

Multiwalled carbon nanotubes (MWCNTs) with unusual rough surfaces (including pits) have been synthesised by the chemical vapour decomposition process of acetylene using a novel Ca₃(PO₄)₂–CaCO₃ support mixture. An Fe–Co bimetallic mixture (50?:?50, w/w) was impregnated (5?wt% loading) onto either Ca₃(PO₄)₂ to give <1% MWCNTs or CaCO₃ to give high yields of MWCNTs with smooth surfaces. Mixtures of Ca₃(PO₄)₂–CaCO₃ (0/100–100/0) yielded tubes with very rough surfaces (t?=?30?min, 1?h) and the CNT yield increased with respect to the amount of CaCO₃ in the support mixture. The inner walls of the CNTs possessed a regular orientation of crystalline graphite sheets (3–5?nm), while the outer surface of the CNTs had a thick, rough, compact layer (～30?nm) of carbon with a random orientation of graphite sheets. These induced extremely rough surfaces of the CNTs could serve as ‘docking stations’ that can harbour a variety of metal catalyst particles for industrially important applications.     

Effect of configurational entropy on dielectric properties of high-entropy perovskite oxides (Ce0.5,K0.5)x[(Bi0.5,Na0.5)0.25Ba0.25Sr0.25Ca0.25]1−xTiO3

Journal of Materials Science: Materials in Electronics - A new kind of high-entropy perovskite oxides (Ce,K)x[(Bi,Na)BaSrCa]1?xTiO3 (x-CKBNBSCTO) were synthesized by using a traditional...     

LuTaO4:Ln3+(Ln=Eu,Tb)透明薄膜制备改进与其发光性能研究

LuTaO₄是一种新型的辐射探测材料, 但是制备高质量的透明薄膜面临着巨大挑战。为了在保证薄膜不开裂与高透明度的前提下提高薄膜的厚度, 通过大量摸索选用聚乙烯吡咯烷酮(PVP)为胶黏剂并优化溶胶中固含量及PVP含量成功制备出单层厚度达到100 nm的LuTaO₄:Ln³⁺(Ln=Eu,Tb)薄膜, 保证了薄膜的透明度同时大大提高了发光性能。该方法为高质量LuTaO₄:Ln³⁺(Ln=Eu,Tb)厚膜的制备和应用奠定了基础。     

Electrical behaviour of La1.33−xM3xTi2O6 perovskites (M=Li,Na and K)

Structural characterization and ionic conductivity properties of the La_1.33−xM_3xTi₂O₆ (M=Li, Na and K) perovskite-type series are reported. From X-Ray diffraction data two different symmetries, tetragonal and orthorhombic, were observed as a function of the ionic size of alkaline cations as well as their proportion in the compounds. Crystallographic features seem to influence on the two possible conduction mechanisms. Orthorhombic samples allow the charge carriers motion through a 3D pathway whereas in the tetragonal ones mobile cations only can move into the A-planes in which are located.