Doped Specimens Research Articles

High-temperature thermoelectric properties of La and Fe co-doped Ca–Co–O misfit-layered cobaltites consolidated by spark plasma sintering

A series of Ca3Co4−yFeyO9 and Ca3−xLaxCo4−yFeyO9 ceramics was prepared by sol–gel method followed by spark plasma sintering. The X-ray diffraction analysis indicates that Fe is substituted at the Co-site in rock salt Ca2CoO3 layers. The partial substitution of Fe at Co-site shows a simultaneous increase in the electrical conductivity and thermopower, which results in an increased power factor. For (La, Fe) co-doped specimens, although, the electrical conductivity is decreased but the thermopower is increased sufficiently to obtain a higher power factor. The temperature dependent electrical conductivity data represents that hole-hopping is the dominant conduction mechanism for all the pure and doped specimens above 573K. The thermal conductivity is greatly suppressed by (La, Fe) co-doping because of the increased phonon scattering. A larger ZT value of 0.32 at 1000K was achieved with (La, Fe) co-doping which is about 70% higher than that of pure Ca3Co4O9.

Sol–gel derived Al and Ga co-doped ZnO thin films: An optoelectronic study

Al and Ga co-doped ZnO (AGZO) thin films with different doping contents of 0.5–4at.% were synthesized via sol–gel route using dip coating method and the results were compared to the single doped specimens Al:ZnO (AZO) and Ga:ZnO (GZO). All samples were highly transparent in visible region (T>85%) with band gap values around 3.3eV. Introduction of Al and Ga to the ZnO crystal structure decreased the crystallinity and reduced the particle size of the films. Electrical resistivity was investigated and engineered in this study as the main parameter. Single doped samples showed reduction of resistivity compared to the un-doped ZnO. In this regard, Ga was more efficient than Al in decreasing the electrical resistivity. Furthermore, samples with 1at.% Al and 1at.% Ga showed the minimum amount of electrical resistivity. Co-doping was performed with two different approaches including variable doping content (Al+Ga≠cte) and constant doping content (Al+Ga=0.5, 1, and 2at.%) for the sake of the comparison with single doped samples. Samples with Al=1at.% and Ga=1at.% showed the lowest electrical resistivity in AGZO samples of former approach. However, in latter approach the lowest resistivity was obtained in Al+Ga=2at.% sample. The results proved the capability of co-doped samples in optoelectronic industry regarding partially substitution of expensive Ga with Al and obtaining co-doped AGZO transparent conductive thin films with lower resistivity compared to conventional AZO thin films and also achieving commercial advantages compared to costly GZO thin films.

Doping concentration dependence on VUV luminescence of Tm:CaF2

Luminescence and scintillation properties of Tm3+ 0.1–15% doped CaF2 crystals were systematically investigated. The crystals were grown by a simple solidification method which allowed us to obtain single crystals conveniently. In X-ray induced radio luminescence spectra, the luminosity of the self-trapped-exciton (STE) emission of CaF2 at 270nm decreased with increasing of Tm3+ concentration. The Tm3+ 5d-4f transition based emission lines appeared at 175nm (4f115d high spin state (HS)→3H6) and at 165nm (low spin state (LS) to 3H6). Pulse height spectra were measured under α-ray irradiation by using vacuum ultra-violet (VUV) sensitive photomultiplier tube (PMT) R8778 and Tm3+ 0.1% doped specimen exhibited the highest light yield.

Co-doping of (Bi0.5Na0.5)TiO3: secondary phase formation and lattice site preference of Co

Bismuth sodium titanate (Bi0.5Na0.5)TiO3 (BNT) is considered to be one of the most promising lead-free alternatives to piezoelectric lead zirconate titanate (PZT). However, the effect of dopants on the material has so far received little attention from an atomic point of view. In this study we investigated the effects of cobalt-doping on the formation of additional phases and determined the preferred lattice site of cobalt in BNT. The latter was achieved by comparing the measured x-ray absorption near-edge structure (XANES) spectra to numerically calculated spectra of cobalt on various lattice sites in BNT. (Bi0.5Na0.5)TiO3 + x mol% Co (x = 0.0, 0.5, 1.0, 2.6) was synthesized via solid state reaction. As revealed by SEM backscattering images, a secondary phase formed in all doped specimens. Using both XRD and SEM-EDX, it was identified as Co2TiO4 for dopant levels >0.5 mol%. In addition, a certain amount of cobalt was incorporated into BNT, as shown by electron probe microanalysis. This amount increased with increasing dopant levels, suggesting that an equilibrium forms together with the secondary phase. The XANES experiments revealed that cobalt occupies the octahedral B-site in the BNT perovskite lattice, substituting Ti and promoting the formation of oxygen vacancies in the material.

The effect of light doping on the creep of β-Sn single crystals induced by superconducting transition

Yield strength and characteristics of the transient creep in β-Sn single crystals doped with substitutional impurities In, Cd, Zn at the concentration of 0.01 at. % were measured at T = 1.6 K. The transient creep in samples with (100) 〈010〉 plastic slip orientation was observed after their normal–superconducting transition. As was earlier shown by the authors, plastic flow in such a slip system in pure β-Sn at low temperatures is determined by the dislocations overcoming Peierls barriers through the mechanism of nucleation and expansion of paired kinks (fluctuation creep stage) or over-barrier dislocation motion (dynamic creep stage). Comparison of the creep behavior in the pure and doped specimens allowed obtaining the information on the influence of impurity atoms on kinetics and dynamics of the motion of dislocation string in Peierls energy landscape. It was found that In and Cd impurities form weak obstacles for dislocations and cause a minor increase in yield strength while stimulating the dynamic creep stage. On the contrary, Zn atoms produce high barriers for dislocation motion, significantly increase the yield point and strongly reduce the contribution of dynamic effects.

Effect of metal chloride solutions on coloration and biaxial flexural strength of yttria-stabilized zirconia

The effect of three kinds of transition metal dopants on the color and biaxial flexural strength of zirconia ceramics for dental applications was evaluated. Presintered zirconia discs were colored through immersion in aqueous chromium, molybdenum and vanadium chloride solutions and then sintered at 1450 °C. The color of the doped specimens was measured using a digital spectrophotometer. For biaxial flexural strength measurements, specimens infiltrated with 0.3 wt% of each aqueous chloride solution were used. Uncolored discs were used as a control. Zirconia specimens infiltrated with chromium, molybdenum and vanadium chloride solutions were dark brown, light yellow and dark yellow, respectively. CIE L*, a*, and b* values of all the chromium-doped specimens and the specimens infiltrated with 0.1 wt% molybdenum chloride solution were in the range of values for natural teeth. The biaxial flexural strengths of the three kinds of metal chloride groups were similar to the uncolored group. These results suggest that chromium and molybdenum dopants can be used as colorants to fabricate tooth colored zirconia ceramic restorations.

Effect of La3+ on microwave dielectric properties of (Pb1− x Ca x )(Fe0.5Nb0.5)O3 (x = 0.5–0.6) ceramics

Abstract Microwave dielectric properties of La3+-doped (Pb1− x Ca x )(Fe0.5Nb0.5)O3 (x = 0.5–0.6) ceramics were investigated, and a superstructure was detected in these ceramics. The dielectric constant (∊r) and the temperature coefficient of the resonant frequency (TCF) decreased, while the Qf value of the specimens increased with the increase in Ca2+ content. At the same Ca2+ content, the ∊r and Qf values of La3+-doped specimens were much higher than those of undoped ones. This is attributed to the elimination of oxygen vacancies by the solid solution of surplus La3+ with (Pb, Ca)2+. Excellent microwave dielectric properties of Qf = 6795 GHz, ∊r = 96.41 with TCF = −4.99 ppm · K−1 were obtained at x = 0.55.

Influence of Vo(II) doping on the thermal and optical properties of magnesium rubidium sulfate hexahydrate crystals

We have prepared pure and divalent vanadyl ion-doped magnesium rubidium sulfate hexahydrate crystals by using slow evaporation solution growth technique. It is interesting to observe that Vo(II) doping influences the physical properties of MRSH. Presence of Vo(II) ions in the doped specimen was confirmed by energy dispersive spectroscopy and electron paramagnetic resonance spectroscopy. FTIR studies reveal that the doping of vanadium ion has not altered the basic structure of MRSH. Scanning electron microscope studies of doped sample reveals that structure defect centers are formed in the crystals. Gradual decomposition patterns were observed for pure and doped specimens in thermogravimetry and differential thermogravimetry. The grown crystals were also characterized by powder X-ray diffraction. The second harmonic generation efficiency tested using Kurtz powder technique is not influenced by the added dopant.

Cation substitution in synthetic meridianiite (MgSO4·11H2O) I: X-ray powder diffraction analysis of quenched polycrystalline aggregates

Meridianiite, MgSO4·11H2O, is the most highly hydrated phase in the binary MgSO4–H2O system. Lower hydrates in the MgSO4–H2O system have end-member analogues containing alternative divalent metal cations (Ni2+, Zn2+, Mn2+, Cu2+, Fe2+, and Co2+) and exhibit extensive solid solution with MgSO4 and with one another, but no other undecahydrate is known. We have prepared aqueous MgSO4 solutions doped with these other cations in proportions up to and including the pure end-members. These liquids have been solidified into fine-grained polycrystalline blocks of metal sulfate hydrate + ice by rapid quenching in liquid nitrogen. The solid products have been characterised by X-ray powder diffraction, and the onset of partial melting has been quantified using a thermal probe. We have established that of the seven end-member metal sulfates studied, only MgSO4 forms an undecahydrate; ZnSO4 forms an orthorhombic heptahydrate (synthetic goslarite), MnSO4, FeSO4, and CoSO4 form monoclinic heptahydrates (syn. mallardite, melanterite, bieberite, respectively), and CuSO4 crystallises as the well-known triclinic pentahydrate (syn. chalcanthite). NiSO4 forms a new hydrate which has been indexed with a triclinic unit cell of dimensions a = 6.1275(1) A, b = 6.8628(1) A, c = 12.6318(2) A, α = 92.904(2)°, β = 97.678(2)°, and γ = 96.618(2)°. The unit-cell volume of this crystal, V = 521.74(1) A3, is consistent with it being an octahydrate, NiSO4·8H2O. Further analysis of doped specimens has shown that synthetic meridianiite is able to accommodate significant quantities of foreign cations in its structure; of the order 50 mol. % Co2+ or Mn2+, 20–30 mol. % Ni2+ or Zn2+, but less than 10 mol. % of Cu2+ or Fe2+. In three of the systems we examined, an ‘intermediate’ phase occurred that differed in hydration state both from the Mg-bearing meridianiite end-member and the pure dopant end-member hydrate. In the case of CuSO4, we observed a melanterite-structured heptahydrate at Cu/(Cu + Mg) = 0.5, which we identify as synthetic alpersite [(Mg0.5Cu0.5)SO4·7H2O)]. In the NiSO4- and ZnSO4-doped systems we characterised an entirely new hydrate which could also be identified to a lesser degree in the CuSO4- and the FeSO4-doped systems. The Ni-doped substance has been indexed with a monoclinic unit-cell of dimensions a = 6.7488(2) A, b = 11.9613(4) A, c = 14.6321(5) A, and β = 95.047(3)°, systematic absences being indicative of space-group P21/c with Z = 4. The unit-cell volume, V = 1,176.59(5) A3, is consistent with it being an enneahydrate [i.e. (Mg0.5Ni0.5)SO4·9H2O)]. Similarly, the new Zn-bearing enneahydrate has refined unit cell dimensions of a = 6.7555(3) A, b = 11.9834(5) A, c = 14.6666(8) A, β = 95.020(4)°, V = 1,182.77(7) A3, and the new Fe-bearing enneahydrate has refined unit cell dimensions of a = 6.7726(3) A, b = 12.0077(3) A, c = 14.6920(5) A, β = 95.037(3)°, and V = 1,190.20(6) A3. The observation that synthetic meridianiite can form in the presence of, and accommodate significant quantities of other ions increases the likelihood that this mineral will occur naturally on Mars—and elsewhere in the outer solar system—in metalliferous brines.

Influence of multi-component glass on sintering behavior and microwave properties of Zr non-stoichiometricly substituted Ca[(Li1/3Nb2/3)]O3-δ ceramic

A low melting point multi-component glass (Li2O-B2O3-SiO2-CaO-Al2O3) was incorporated into Zr non-stoichiometric substituted Ca[(Li1/3Nb2/3)]O3-δ ceramic to lower its sintering temperature for LTCC applications. The glass acts as liquid phase sintering aid and it can lower the sintering temperature of the ceramic from 1,170 °C to 900 °C. Dense and perovskite solid solutions can be obtained in all glass doped specimens with, however, a small amount of Ca2Nb2O7-type pyrochlore phase. Raman spectra indicate that the B-site 1:2 ordering structure in Ca[(Li1/3Nb2/3)0.95Zr0.15]O3+δ ceramic is gradually softened with the increase of the glass content and localized B-site 1:1 ordering domains begin to appear when the glass content reaches 15 wt%. The optimal microwave dielectric properties of er = 29.37, Qf = 5,420 GHz and τf = −24.9 ppm/°C can be obtained in 5 wt% glass doped Ca[(Li1/3Nb2/3)0.95Zr0.15]O3+δ ceramic when sintered at 940 °C for 4 h. No chemical reaction exists between Ag and the above ceramic, which indicates itself a potential candidator in LTCC industry.

Conductivity and electrical modulus studies of La2−x Nd x Mo1.7W0.3O9−δ oxygen ion conductor

La2−xNdxMo1.7W0.3O9−δ (x = 0 − 0.5) and, for comparison, La2Mo2O9 compounds have been synthesized following solid state reaction technique. Temperature-dependent electrical conductivity of La2−xNdxMo1.7 W0.3O9−δ reveals suppression of the phase transition as compared to parent La2Mo2O9 compound. Partial substitution of Nd at the La site of La2Mo1.7W0.3O9−δ increases the conductivity of La2Mo1.7W0.3O9−δ in the entire temperature regime. In the intermediate temperature region (405 °C ≤ T ≤ 570 °C), the overall conductivity of La2−xNdxMo1.7W0.3O9−δ (0.1 ≤ x ≤ 0.5) is higher than that of the parent compound, and the conductivity of the compound with x = 0.1 is almost same with the La2Mo2O9 in the high temperature region (T ≥ 640 °C). Arrhenius to Vogel–Tamman–Fulcher (VTF) transition is observed in all doped specimens above 460 °C. Ion relaxation mechanism has been discussed in the framework of electrical modulus analysis in the temperature range RT–530 °C and is found to be non-Debye type of conductivity relaxation with the distribution of transition rates for hopping ions in the range of 0.60–0.70.

Doped ions (Co2+, Fe3+) tuning morphologies and magnetic properties of indium oxide nanoparticles

Transition-metal ion-doped indium oxide was potentially used in spintronic devices. In this article, 10 at.% Co2+- and Fe3+-doped indium oxide nanocrystals were, respectively, prepared by direct solvothermal method. The influences of doped ions on their morphologies and magnetic properties of indium oxide nanocrystals were investigated. It was found that the doped ions could tune the microscopic morphologies and crystalline structures of indium oxide nanoparticles. Co2+-doped samples were polycrystalline nanoflowers aggregated by about 5 nm nanocrystals while Fe3+-doped specimens were single-crystalline nanocubes with crystalline sizes of about 16 nm. Meanwhile, the magnetic transition from diamagnetism to paramagnetism was also realized by doping Co2+ or Fe3+ ions into the indium oxide host matrices. In addition, their magnetic properties were further demonstrated to be intrinsic and not caused by impurities.

The concentration effects of s-, p-, d- and f-block element doping on the growth, crystalline perfection and properties of KDP crystals

The effect of dopants (over a wide concentration range from 0.5 to 10 mol%), namely s-, p-, d- and f-block elements (Mg, Sb, Pd and La) on the growth process, crystalline perfection, external morphology, vibrational patterns, XRD profile and second order nonlinear optical (NLO) properties of potassium dihydrogen phosphate (KH2PO4, KDP) crystals grown by the slow evaporation solution growth technique has been systematically investigated. Incorporation of the dopants into the crystalline matrix even at low concentrations was well confirmed by the inductively coupled plasma (ICP) technique. The change in intensity patterns in XRD profiles of doping specimens reveals lattice distortion, further supported by slight shifts in characteristic vibrational frequencies in FT-IR. The scanning electron microscope (SEM) micrographs exhibit the effectiveness of the impurity in varying the surface morphology. The high-resolution X-ray diffraction (HRXRD) studies used to evaluate the crystalline perfection reveal many interesting features on the ability of accommodating the dopants by the crystalline matrix. It appears that the crystalline perfection depends mostly on the concentration of the dopant. Multi-peaks appear for highly doped specimens indicating the inhomogeneous accommodation. The second harmonic generation (SHG) efficiency is enhanced considerably when the concentration of the dopant is low while depressed activity is observed with poor crystalline perfection at high concentrations irrespective of the nature of the dopants.

Physicochemical properties and cellular responses of strontium-doped gypsum biomaterials.

This paper describes some physical, structural, and biological properties of gypsum bioceramics doped with various amounts of strontium ions (0.19–2.23 wt%) and compares these properties with those of a pure gypsum as control. Strontium-doped gypsum (gypsum:Sr) was obtained by mixing calcium sulfate hemihydrate powder and solutions of strontium nitrate followed by washing the specimens with distilled water to remove residual salts. Gypsum was the only phase found in the composition of both pure and gypsum:Sr, meanwhile a shift into lower diffraction angles was observed in the X-ray diffraction patterns of doped specimens. Microstructure of all gypsum specimens consisted of many rod-like small crystals entangled to each other with more elongation and higher thickness in the case of gypsum:Sr. The Sr-doped sample exhibited higher compressive strength and lower solubility than pure gypsum. A continuous release of strontium ions was observed from the gypsum:Sr during soaking it in simulated body fluid for 14 days. Compared to pure gypsum, the osteoblasts cultured on strontium-doped samples showed better proliferation rate and higher alkaline phosphatase activity, depending on Sr concentration. These observations can predict better in vivo behavior of strontium-doped gypsum compared to pure one.

Ni<SUP>2+</SUP> Doped Indium Oxide Nanocubes: Doped Contents Inducing Transferring of Their Intrinsic Magnetisms

A series of Ni2+ doped indium oxide nanocubes with different Ni2+ contents (nominally from 3 at.% to 20 at.%) were prepared by direct solvothermal method. We found that the highest Ni2+ doped percentage was 20 at.% in the experiment and crystalline sizes of these Ni2+ doped indium oxide specimens linearly increased with increments of doped contents and then decreased. Meanwhile, their magnetisms were also transferred from ferromagnetism to paramagnetic properties due to the stronger Ni-O-Ni paramagnetic chemical bonds. HRTEM, SAED and XRD further confirmed their magnetic properties were intrinsic and not caused by second impure phases.

Low energy Xe milling for the quantitative profiling of active dopants by off-axis electron holography

Off-axis electron holography is a powerful technique that can be used to measure the active dopants in semiconductors. The preparation of thin transmission electron microscopy specimens containing nm-scale regions of interest is extremely challenging and as a consequence ion milling is an essential tool. The exposure of doped specimens to energetic ions creates defects deep in the specimens that trap the active dopants, being the principle cause of what is known as the inactive region. The inactive thickness leads to an underestimation of the dopant potential in the specimens. Here we show that this artifact can be significantly reduced from 140 nm for specimens prepared using only Ga ions at 30 kV to only 10 nm by preparing specimens using 1.5 keV Xe ions for specimens containing p-n junctions with dopant concentrations of 2 × 1018 cm−3.

Effect of nonmagnetic alkaline-earth dopants on magnetic properties of BiFeO3 thin films

Bi0.95A0.05FeO3 (A = Ba, Sr, Ca) thin films were deposited on (111) Pt/Ti/SiO2/Si substrates via chemical solution deposition. The magnetization of the doped specimens increases sharply as compared to that of pure BiFeO3, and it increases as the doped ionic radius gets larger. X-ray diffraction analysis reveals that the films are single phase, and no other extra magnetic phases are detected. X-ray photoelectron spectroscopy analysis suggests that the content of Fe3+ increases and that that of Fe2+ decreases. According to the x-ray diffraction and Raman analyses, there are corresponding changes in the lattice parameters and the Raman spectra as the doped ionic radius gets larger. These results indicate that neither the magnetic coupling of Fe2+ nor the parasitic magnetic phases could be the origin of the magnetization improvement, and we consider that the magnetization improvement mainly originates from the doped ionic radius size effect.

Dehydrochlorination of Interpolymer Complexes and Composites of Polyanilines with Poly Acids

The temperature ranges of dehydrochlorination (50–180°C) and degradation (320°C and above) of polyanilines have been determined. A study has been made of the thermal stability of polyaniline interpolymer complexes and composites in a wide temperature range. The activation energy of the dehydrochlorination of doped polyaniline specimens has been established.

Abrasive wear resistance of SiO2-doped polycrystalline alumina

A range of silica-doped alumina ceramics with addition of 0, 0.5, 1, 5 and 10 wt.% of SiO2 was prepared by hot pressing at 1450 °C. Controlled grain growth was achieved by high temperature annealing of hot pressed specimens at 1600 °C. Resistance against wet abrasive wear was tested using custom-built sample holder on a standard grinder/polisher machine. The wear rates increased with increasing rotation speed and loading force, and with size of alumina grains, and decreased with increasing content of SiO2 addition. The measured wear rates were comparable to those of alumina–SiC nanocomposites with similar alumina matrix grain size, but inferior to pure alumina ceramics with submicrometre microstructure. The wear rates of silica doped specimens increased, similarly to monolithic alumina, with the time of high temperature isothermal treatment, which primarily resulted in the growth of alumina grains. The change of the phase composition (crystallisation of low thermal expansion phase mullite) and resulting change of the stress state of the annealed silica doped specimens had negative impact on both the hardness and wear resistance.

The effect of impurity-induced lattice strain and Fermi level position on low temperature oxygen diffusion in silicon

Oxygen diffusion in silicon is known to be affected by high concentrations of impurities, although the mechanism underpinning this is poorly understood. We have studied oxygen transport in Czochralski silicon by analyzing data on the locking of dislocations by oxygen as a function of time and temperature. In this paper, we present new data from crystals grown to contain high levels of germanium and arsenic. We analyze these new data, together with our previous data for silicon with a high boron concentration, to further the understanding of the mechanism by which high impurity concentrations affect oxygen transport at temperatures at which the oxygen dimer dominates transport (up to 550 °C). Our results show that a high level of boron doping (∼3 × 1018cm−3) enhances the effective diffusivity of oxygen by a factor of ∼8 to ∼25 relative to low doped material with the same oxygen concentration. High levels of germanium doping (∼8 × 1019cm−3) and arsenic doping (∼2 × 1019cm−3) can both have a slight retardation effect on oxygen transport. The magnitude of the reduction measured is less than a factor of ∼4 in the heavily germanium doped specimens and less than a factor of ∼5 in the heavily arsenic doped specimens, and in most cases is significantly less than this. Germanium doping introduces considerable strain into the silicon lattice without affecting the Fermi level position, so data from these samples show that lattice strain affects oxygen dimer transport. The arsenic and boron doping levels in the materials studied give rise to lattice strain with a smaller magnitude and opposite sign to that in the germanium doped samples. It is therefore suggested that the Fermi level position also affects the transport of oxygen dimers.