Effect Of Ca Doping Research Articles

Effects of Ca doping on structural and optical properties of PZT nanopowders

The influence of the addition of calcium ions (Ca2+) in the Pb(1-x)CaxZr0.52Ti0.48O3 system (PCZT) for x = 0.05, 0.10, 0.15, 0.20, and 0.25 on the structural and optical properties was systematically studied. The compositions were synthesized through a polymerized-complex approach based on the Pechini polymeric precursor route. The solubility limit of calcium ions within the PCZT lattice is in between x = 0.10 and x = 0.15, at which a CaTiO3 secondary phase is detected. The Goldschmidt tolerance factors, modified tolerance factors, and the effective vacancy sizes were all estimated for the synthesized nanopowders. While the Goldschmidt tolerance factors suggest the formation of a distorted perovskite structure, the values of the modified tolerance factor were extremely close to unity, indicating a strong stable ferroelectric perovskite structure. The optical band gap was found to decrease with calcium concentration to a minimum at x = 0.20 and then slightly increase at x = 0.25.

Three-dimensional Heisenberg critical phenomena in La0.6Bi0.1Sr0.3−xCaxMn0.9Cu0.1O3 manganites (x = 0 and 0.05)

In this paper, our main objective is to study the effect of Ca doping on the critical properties of La0.6Bi0.1Sr0.3−xCaxMn0.9Cu0.1O3 (x = 0 and 0.05). The X-ray diffraction analysis reveal that both specimens are indexed in the rhombohedral structure with R–3c space group. As for the magnetic studies, a second-order ferromagnetic–paramagnetic (FM–PM) phase transition takes place around the transition temperature (TC). Based on different methods such as extrapolation of the Arrott curve, Kouvel-Fisher procedure and critical isothermal analysis depending on the data from magnetic investigations, the examination of the critical behavior was performed. The values of the deduced critical exponent (β, γ, δ) for both compounds proved to be close to those predicted by Heisenberg's 3D model, revealing an inhomogeneous magnetic exchange coupling at short distances. These critical exponents show a good agreement with their corresponding values proven by Widom's law of scale, as well as the theory of scale. Additionally, a typical soft FM behavior with a low coercive field was observed at 10 K according to the hysteresis loops. These outcomes make our compounds good candidates for memory devices and magnetic recording.

Studies on effect of Ca-doping on structure and electrochemical properties of garnet-type Y3-xCaxFe5O12-δ

In this study, effect of Ca-doping on electrical and electrochemical properties of garnet structure Y3-xCaxFe5O12-δ (x ​= ​0, 0.05, 0.1, 0.3, 0.5 and 0.7) was investigated. Cubic-phase (Ia-3d) garnet was prepared through sol-gel method and sintered at 1100 ​°C for 2 ​h in air. Highest oxygen non-stoichiometry (δ ​= ​0.19) was found in x ​= ​0.3 member. X-ray absorption spectroscopy (XAS) confirmed the formation of hole carriers (Fe.Fe) due to Ca-substitution for Y in Y3Fe5O12. 4-Probe DC measurements showed that electrical conductivity increased with an increase in Ca amount until x ​= ​0.1 (1.58 ​S/cm at 750 ​°C) and then decreased due to decrease in the concentration of the charge carriers. Lowest area specific resistance (ASR) of 1 Ωcm2 was seen at 750 ​°C in air for the symmetrical cell with x ​= ​0.3 garnet-LSGM composite electrode. Studies on pO2 dependent ASR and impedance spectroscopy genetic programming (ISGP) analysis revealed that oxygen dissociation and partial reduction of adsorbed oxygen molecule co-limit the electrochemical performance for oxygen reduction reaction (ORR).

Effect of Calcium doping on Structural and Morphological properties of YBCO Superconductor

In this paper, we have reported the effect of Ca doping in YBCO superconductors with an aim of understanding the effect of novel local nano distortions on the superconducting properties of YBCO. Solid state reaction method is used to prepare the samples. X-Ray diffraction pattern shows that the samples are polycrystalline and having orthorhombic structure while Resistivity measurement shows that Tc decreases with increase in Ca-doping.Morphological studies reveals clear evolution of microstructure from a grains and grain boundaries like structure in YBCO and low Ca concentrations to a smooth well connected microstructure upon higher Ca content.

Effect of CaCO3 on catalytic activity of Fe-Ce/Ti catalysts for NH3-SCR reaction.

In the present work, fresh and Ca poisoned Fe–Ce/Ti catalysts were prepared and used for the NH3-SCR reaction to investigate the effect of Ca doping on the catalytic activity of catalysts. And these catalysts were characterized by BET, XRD, Raman, UV-vis DRS, XPS, H2-TPR, and NH3-TPD techniques. The obtained results demonstrate that Ca doping could lead to an obvious decrease in the catalytic activity of catalysts. The reasons for this may be due to the smaller specific surface area and pore volume, the decreased ratio of Fe3+/Fe2+ and Ce3+/Ce4+, as well as the reduced redox ability and surface acidity.

Effect of Ca doping on the properties of Sr2Bi4Ti5O18 ferroelectric thin films

This study examined the effect of Ca doping on the properties of Sr2Bi4Ti5O18 (SBTi) ferroelectric thin films. According to the results of the study, the performance of SBTi thin films are improved by suitable Ca doping. It can be seen from XRD analysis, all of the thin films formed a bismuth layered perovskite structure without other impure phases. SEM shows that the sample with a doping content of 10 mol% has good crystallization, uniform grain size and good film density. Compared with the characteristics of other films, the thin film sample with 10 mol% Ca shows high crystallinity, the lowest Ti3+ content, the lowest oxygen vacancy concentration, and with the large remanent polarization 2Pr = 33.5 μC/cm2, the double coercive field 2Ec = 182.8 kV/cm; furthermore, the leakage current density is 1.67 × 10−7 A/cm2. The film sample doped with 10 mol% Ca also displays better dielectric properties, with a larger dielectric constant (er = 795) and lower dielectric loss (tanδ = 0.03) when the test frequency is 105 Hz. The dielectric tunability T = 18.6% at 200 kV/cm and 500 kHz.

Effect of Ca Doping on the Structure and Magnetic and Electronic Properties of La1 − xCaxCr0.8Cu0.2O3 (x = 0~0.3)

A series of La1 − xCaxCr0.8Cu0.2O3 samples were successfully prepared by sol-gel method, and their crystal structures were refined by using X-ray powder diffraction data. All samples had orthorhombic structure with a space group Pbnm. Two magnetic transitions were observed for all of samples, and the paramagnetism-antiferromagnetism transition temperature decreased, and the antiferromagnetism-ferromagnetism transition temperature increased with increasing Ca content. Moreover, Cu and Ca co-doping improved conductivity and active energy.

Effect of Ca doping on structural, magnetic and electronic properties of TbMnO3

First principles calculations have been carried out to investigate the structural, magnetic and electronic properties of the multiferroic manganite TbMnO3 with and without Ca doping. For pure TbMnO3, results show that spiral-spin antiferromagnetic ordering is energetically found favorable. The presence of Ca doping at the manganite Tb1−xCaxMnO3 with x = 0.25, 0.5 and 0.75 directly affects the Mn ordering. For x ≤ 0.5, the ferromagnetic ordering is most favored. While for x = 0.75, the most stable magnetic configuration is antiferromagnetic arrangement. It is found that the decrease in the intensity of the ferromagnetic double-exchange interaction has been correlated with the increase in the Ca content and the Mn-O-Mn bond angle.

Effect of Ca Doping on the Selective Catalytic Reduction of NO with NH3 Over Ce–Ti Oxide Catalyst

A series of Ca doped Ce–Ti oxides prepared by a single step sol–gel method were investigated for the selective catalytic reduction of NO with NH3. The results show that Ca doping had both positive and negative effects on the activities of Ce–Ti oxide. Ca0.1CT possessed the best catalytic activity and widest temperature window. Further investigations on BET, XRD, XPS, H2-TPR and NH3-TPD demonstrated that the good SCR performance of Ca0.1CT could be attributed to the increase in the amount of Ce3+ and surface adsorbed oxygen as well as the enhancement of Bronsted acidity and redox ability. In addition, the good dispersion of active Ce species, the alleviation of support sintering, and the interaction among Ce, Ti and Ca species were also responsible for its enhanced activity.

Effect of Ca-doping on electrical properties of La0.46Sm0.21Sr0.33-xCaxMnO3 ceramics prepared by sol-gel technique

La0.46Sm0.21Sr0.33−xCaxMnO3 (x = 0.00, 0.05, 0.10, 0.15, and 0.20) ceramics synthesized by Pechini sol–gel method were investigated by X-ray diffraction analysis, scanning electron microscopy, and energy-dispersive spectroscopy. Temperature dependence of resistivity (R-T) was measured using the standard four-probe method. All the samples had single phases of orthorhombic perovskite crystal structure. By substituting Sr ion with Ca ion, the samples achieved high crystalline quality, density, and chemical uniformity. After the substitution, the resistivity of samples decreased, and the metal–insulator (M–I) transition temperature (TP) shifted to a lower temperature, making the M–I transition sharper. Therefore, the temperature coefficient of resistance increased. Moreover, the substitution decreased the A-site average cationic radius , thus decreasing the Mn–O–Mn bond angle. This weakens the double exchange between Mn3+ and Mn4+.

Research Update: Ca doping effect on the Li-ion conductivity in NASICON-type solid electrolyte LiZr2(PO4)3: A first-principles molecular dynamics study

In this work, we used a density functional theory-based molecular dynamics simulation to investigate the Ca content-dependent Li-ion conductivity of NASICON-type Li1+2xCaxZr2-x(PO4)3 (LCZP) solid electrolytes (0.063 ≤ x ≤ 0.375) which exhibit a Li-excess chemical composition. The LCZP systems show a higher room temperature Li-ion conductivity and a lower activation energy than pristine LiZr2(PO4)3 (LZP), and the tendencies of those properties agree with the experimental results. In addition, the Li-ion conduction mechanisms in LCZP were clarified by analyzing the radial distribution functions and site displacement functions obtained from our molecular dynamics simulations. For minimal Ca substitution for LZP, the Li-ion conductivity is enhanced because of the creation of interstitial Li ions by Ca doping in the LCZP systems; the frequency of collisions with Li ions dramatically increases. For substantial Ca substitution for LZP, the Li-ion conductivity gradually worsened because some Li ions were trapped at the M1 (most stable) and M2 (metastable) sites near Ca atoms.

Low Temperature Cofiring and Dielectric Properties of Ca-Doped Al2O3/K2O3–B2O3–SiO2 Composite Ceramics for LTCC Applications

Al2O3/K2O3–B2O3–SiO2 low temperature cofired ceramics (LTCC) dielectric materials doped with CaCO3 were prepared by using a solid-state reaction. The microstructure and dielectric properties of Al2O3/K–B–Si borosilicate, together with the effects of Ca doping, were investigated. A new material system candidate of Al2O3/KBSiO borosilicate doped by Ca was achieved after sintering at 880°C, which presents an optimized performance on dielectric properties with a permittivity εr < 8 and dielectric loss tan δ ≤ 0.002 and excellent stabilities across very broad frequency and temperature ranges. Most importantly, the initial results have also indicated that the new dielectric composite material is well compatible with the existing LTCC process, suggesting a considerable potential for practical LTCC applications.

Investigation of layered perovskite NdBa0.5Sr0.25Ca0.25Co2O5+δ as cathode for solid oxide fuel cells

Layered perovskite oxides with and without Ca-doped NdBa0.5Sr0.25Ca0.25Co2O5+δ (NBSCaCO) and NdBa0.5Sr0.5Co2O5+δ (NBSCO) are studied to investigate the effects of Ca doping on the crystal structure, thermal behavior, electrical and electrochemical properties. Both NBSCO and NBSCaCO are tetragonal structure with P4/mmm space group. The average thermal expansion coefficient (TEC) value is reduced from 23.3 × 10−6 K−1 to 19.8 × 10−6 K−1 during 30–800 °C. The electrical conductivities are increased by Ca doping. Both electrical conductivities of NBSCO and NBSCaCO are higher than 600 S·cm−1 over 30–800 °C. Substitution of Sr with Ca can effectively improve the electrochemical properties of NBSCaCO. From 650 °C to 800 °C, the area specific resistance (ASR) of NBSCaCO are decreased from 0.62 to 0.062 Ω cm2 and the corresponding output power density are increased from 258 to 812 mW cm−2. On the basis of these results, Ca doped layered perovskite NBSCaCO can be a good cathode candidate material for SOFC application.

Simultaneously enhanced piezoelectric properties and depolarization temperature in calcium doped BiFeO3-BaTiO3 ceramics

Polycrystalline piezoelectric ceramics 0.7Bi1-xCaxFeO3-0.3BaTiO3 (BCxF-BT) were fabricated by the solid state reaction route. Effects of Ca doping on microstructures, electrical properties and their temperature dependence were investigated systematically. The results show that Ca doping has little influence on crystal structure, while significant grain growth takes place. Improved piezoelectric properties with d33 = 168 pC/N, kp = 0.28 and Smax = 0.146%, concurrently with high temperature stability (Td = 420 οC and Tm = 438 οC) are obtained for 0.75% Ca doped ceramics. The high degree poling induced domain texture and improved stability of long-range ferroelectric state at high temperature may be responsible for the enhanced piezoelectric properties and depolarization temperature respectively. The results indicate that Ca doped BCxF-BT lead-free piezoceramics are intriguing for applications in high-temperature sensor and actuator.

Oxygen transport properties of Ca-doped Pr2NiO4

Praseodymium nickelate Pr2NiO4+δ with layered Ruddlesden–Popper (R–P) structure is a promising material for the ceramic membranes for oxygen separation and for SOFC cathodes due to its mixed ionic-electronic conducting nature and high oxygen mobility and surface reactivity. However, a low thermal stability and the inadequate electronic conductivity of Pr2NiO4+δ require its doping for a more efficient performance. This work presents results of study of the effect of Ca doping on the structural and transport properties of Pr2NiO4. Pr2−xCaxNiO4 oxides (x = 0–0.6) were synthesized by a co-precipitation method and characterized by XRD, XPS and TEM methods. The oxygen content in these materials and its variation with increasing temperature was evaluated using TGA. The oxygen transport properties of powdered samples were studied by the temperature-programmed oxygen isotope heteroexchange with C18O2 (TPIE). Electrical conductivity of compact samples was measured by a dc four-probe technique. Electrochemical measurements were performed using an impedance spectroscopy method with symmetrically arranged electrodes on the Ce0.8Sm0.2O1.9 electrolyte. It was shown that doping resulted in enhanced electrical conductivity and at a low Ca content the electrochemical activity of electrodes increased while the interstitial oxygen content and oxygen diffusivity gradually decreased. For x > 0.3 increasing the lattice anisotropy resulted in the co-existence of 2–3 channels of oxygen diffusion revealed as separate peaks in TPIE curves. The fast diffusion channel (D⁎ ~ 10−8 cm2/s at 700 °C), with a share in the total diffusion drastically decreasing at big doping levels, corresponds to the fast interstitial oxygen diffusion via the cooperative mechanism while the slow channels (D⁎ < 10−10 cm2/s) are probably related to the oxygen transport in perovskite layers and the complicated transport involving interlayer positions near the dopant cation sites.

Experimental and theoretical investigation on tunable optical property of nanocrystalline Ca-doped CeB6

Nanocrystalline Ca-doped CeB6 powders have been synthesized via a solid-state reaction of CaO and CeO2 with NaBH4 under a vacuum condition. The Ca doping effects on phase composition, grain morphology and optical absorption properties of nanocrystalline CeB6 were investigated. As a result, all the synthesized nanocrystalline hexaborides are composed by single phase of CsCl-type structure. The grain size and morphology are very sensitive to the reaction temperature. The optical absorption result indicates that the absorption valley of nanocrystalline CeB6 shows a red-shift from 619 nm to 685 nm with increasing Ca doping content, which means the tunable optical absorption of nanocrystalline Ca-doped CeB6. In addition, a first-principles calculation has been used to reveal the origin of the tunable optical properties. It is found that Ca doping reduces the total kinetic energy of the electrons of CeB6 and leads to the absorption valleys shift to longer wavelength direction.

Ca doping effect on the magnetic and electronic transport properties in double perovskite PrBaCo2O5+δ films

Ca doped double perovskite PrBa1-xCaxCo2O5+δ (x = 0, 0.3, and 0.5) thin films were epitaxially grown on the (001) SrTiO3 substrates to systematically investigate the A′ site doping effect on the magnetic and electronic transport properties. With the increase in the Ca content, the magnetization measurements on the films show that the magnetic moments are significantly increased and the largest magnetic moment of 88 emu/cm3 can be achieved in the film with x = 0.5 or about 90 times larger than that from the undoped PrBaCo2O5+δ film. The electronic transport property measurements on the films indicate that the electrical conductivity can be altered by various Ca doping contents. It is interesting to note that both undoped PrBaCo2O5+δ and PrBa0.5Ca0.5Co2O5+δ films exhibit simple activation behavior, but the PrBa0.7Ca0.3Co2O5+δ film exhibits the 3D variable-range hopping mode conduction.

Effect of Ca-doping on the electrical properties of La0.2Nd0.47Sr0.33MnO3 ceramics prepared by sol–gel technique

A series of ceramic samples La0.2Nd0.47Sr0.33−xCaxMnO3 (x = 0.00, 0.03, 0.06, 0.09 and 0.12) were prepared by sol–gel technique. The crystal structure was analyzed by X-ray diffraction, which reveals that all the samples are single-phase without any detectable secondary phases. The grain size and surface morphology were investigated by scanning electron microscope ,which indicates that ceramic samples with better crystallization have high density. The resistivity dependence of the temperature (R-T) of the bulk samples was studied by the standard four-probe method. The result of the R-T curves shows that the metal-insulator transition temperature shifts to the lower temperature and the resistivity as well as the maximum value of the temperature coefficient of resistivity increase. It is usually interpreted as the Ca-doping decreases the A-site cationic radius and the tolerance factor, which results in MnO6 octahedral tilting and the decrease of the double exchange between Mn3+ and Mn4+.

Effect of Ca2+ substitution on impedance and electrical conduction mechanism of Ba1−xCaxZr0.1Ti0.9O3 (0.00≤x≤0.20) ceramics

The Ca modified Ba1−xCaxZr0.1Ti0.9O3 (BCZT) system for x=0.00–0.20 is synthesized by the high-temperature conventional solid state reaction method. The morphotropic phase boundary (MPB) between the tetragonal and cubic structure is obtained at room temperature for the composition x=0.15. The doping of Ca facilitates the enhancement of the homogeneity of microstructure and growth of the grain size. The phase transition is also confirmed by Raman spectroscopy. In order to explore the effect of Ca concentration variation on the conduction mechanism of BaZr0.1Ti0.9O3 (BZT) ceramic, the frequency dependent ac impedance spectroscopy technique is used at various temperatures. The effect of Ca doping on the electrical properties of BZT is clearly noticeable. The resistance of the grain (bulk) and the grain boundary is increased as a consequence of the increase in the activation energy of Ca substituted BZT samples. The enhanced resistivity of the Ca substituted BZT ceramics is explained in terms of the decrease in the mobility of the charge carriers associated with the lattice distortion. The electric modulus analysis reveals the enhanced capacitance of BCZT ceramics which is in good agreement with the results obtained from complex impedance analysis.

Effect of Ca-Doping on the Structure and Morphology of Polycrystalline La0.7(Ba1-xCax)0.3MnO3 (x = 0; 0.03; and 0.05)

In this paper, we report structure and morphology of polycrystalline La0.7(Ba1-xCax)0.3MnO3 (x = 0; 0.03; 0.05). Basically, these materials are perovskite manganites type with the general structure AMnO3 (A= trivalent rare earth with divalent ion-doped) which have been extensively studied due to their interesting physical properties. It was known that the electron transport in this material influenced by ion doped at A site. Doping with different divalent ions should cause the lattice distortion. Hence, double exchange interaction is enhanced. In this study, we prepared our sample through the sol-gel method. It is show that the method has resulted in powder materials with ultra-fine particle size. The effect of Ca+2 and Ba+2 doping on the structure did not make any phase changing, but the lattice parameter of La0.7(Ba1-xCax)0.3MnO3 decreased below × = 0.03. Microstructure observed by scanning electron microscope to the sintered samples indicated that the microstructure is homogeneous with fine size of equiaxed grain morphology. Microanalysis by EDS confirmed there is no significant different between designated composition and measured one. It is concluded that effect of Ca+2 and Ba+2 doped in LaMnO3 has resulted in microstructural and lattice parameter changes. The doped materials are remaining single phase.