Step Solid State Reaction Method Research Articles

OSL and TA-OSL properties of Li2B4O7:Al for radiation dosimetry

Lithium tetraborate is one of the tissue equivalent material that has been modified with numerous dopant/codopant to improve its Thermoluminescence and Optical stimulated Luminescence properties. Lithium tetraborate doped with Aluminum is being investigated for Optical stimulated Luminescence dosimetry in this paper. Polycrystalline nano-phosphor samples were synthesized using two step solid state reaction method with optimized concentration of Aluminum equals to 2% (by wt.). Formation of the same and its morphology was confirmed using X-ray Diffractometry and Transmission Electron Microscopy. The various dosimetric properties of the obtained phosphor along with related Optical stimulated Luminescence kinetic parameters have been studied. The phosphor exhibits good linearity for gamma radiation in the range of 0.1–500 Gy with other properties such as low fading, satisfactory reusability & reproducibility and minimum detectable dose of 0.05 Gy. In this paper we have also explored the Temperature-Assisted Optical stimulated Luminescence properties of the obtained phosphor in the range of 25 ֯C to 200 ֯C and the optimized temperature corresponding to the maximum Optical stimulated Luminescence intensity was found to be 125 ֯C with activation energy equals to 0.108 ± 0.02 eV. The studied nanophosphor has also shown linear response with dose gamma (1–200 Gy) and beta (0.05–3 Gy) at 125 ֯C. • Tissue equivalent Li 2 B 4 O 7 :Al nanophosphor is developed using solid state reaction with two stage heating process. • The optimized level of Al doping in Li 2 B 4 O 7 shows non-toxic, robust response for reusable dosimetry. • CW-OSL/TA-OSL studies of gamma and beta irradiated Li 2 B 4 O 7 :Al are reported for the first time. • Linear CW-OSL/TA-OSL response in the observed dose range has been observed. • Optimized elevated temperature corresponding to the maximum OSL intensity is found to be 125 ֯C. • Activation energy equals 0.108±0.02 eV is calculated using Arrhenius equation.

Effect of Cd intercalation on the superconducting properties of (Cu0.5-yKyTl0.5)Ba2Ca2Cu3-xCdxO10-δ (y = 0, 0.25; x = 0, 0.5, 1.0, 1.5, 2.0) superconductors

(Cu0.5Tl0.5)Ba2Ca2 Cu3-xCdxO10-δ (x = 0, 0.5, 1.0, 1.5, 2.0) samples are synthesized for the investigation of role of an-harmonic oscillations in the mechanism of high Tc superconductivity. The density of carriers in the conducting planes is enhanced with the doping of K at the (Cu0.5Tl0.5)Ba2O4-δ by synthesizing (Cu0.25K0.25Tl0.5)Ba2Ca2Cu3-xCdxO10-δ (x = 0, 0.5, 1.0, 1.5, 2.0) samples. These samples were synthesized by two step solid state reaction method accomplished at 860 °C and studied their superconducting properties by resistivity measurements, X-ray diffraction analysis and FTIR absorption measurements. The planar reflections observed in the XRD analysis of the samples are best fitted to the orthorhombic crystal structure. The c-axis length and the volume of the unit cell increases with the enhanced doping of Cd in the final compound. The onset temperature of superconductivity Tc (onset) and the zero-resistivity critical temperature Tc (R = 0) suppresses with the increased doping of Cd in the final compound. An improvement in the Tc (onset) and Tc (R = 0) is observed in K-doped samples that arises due to increase in the density of free carriers supplied by alkali atoms. A softening of apical oxygen mode of type Cu(1)‒OA‒Cu(2)/Cd is observed with the increased doping of Cd at the CuO2 planar sites. The apical oxygen mode of type Tl‒OA‒Cu(2)/Cd is, however, did not change with the doping of Cd in the final compound. The planar oxygen mode (545 ‒ 570 cm−1) is hardened with the enhanced doping of Cd in the final compound. The excess conductivity analyses of conductivity data have shown a shift in the various cross-over temperatures, Tcmf and T* towards lower temperatures with the enhanced doping of Cd in the final compound. The value of α determining the defect density also increases with the increased doping of Cd in the final compound. The coherence length along the c-axis ξc(0), interlayer coupling J, magnetic field penetration depth λp.d and Ginzburg Landau (GL) parameter κ decreased with the increase doping of Cd. The phase relaxation time of the carriers Ꞇϕ, the Fermi velocity VF of the carriers decreased while Bc0(T), Bc1(T) and Jc (0) are enhanced with increase doing of Cd in the final compound.

Isovalent Substitution Effects of Arsenic on Structural and Electrical Properties of Iron-Based Superconductor NdFeAsO0.8F0.2

In this paper, nominal compositions of NdFeAsO0.8F0.2, NdFeAs0.95Sb0.05O0.8F0.2 and NdFeAs0.95P0.05O0.8F0.2 were prepared by one step solid state reaction method. The structural, electrical and morphological properties of samples were characterized through the XRD pattern, the 4 probe method and SEM, respectively. The crystal structure of our samples was tetragonal with P4/nmm:2 symmetry group. Also, the (x, y, z) and occupancy of ions and lattice parameters were changed by isovalent substitution of Phosphorus P and Antimony Sb in the NdFeAsO0.8F0.2 sample. The alfa and beta bond angles and Fe-As bond length are changed from the corresponding value of alfa and beta regular FeAs4 tetrahedron by isovalent doping p/As and Sb/As, that they are effective on the superconductivity transition temperature. The microstrain and crystalline size of samples were studied by the Williamson Hall method. The superconducting critical temperatures were attained at 56K and 46K for NdFeAsO0.8F0.2, NdFeAs0.95Sb0.05O0.8F0.2, respectively. The NdFeAs0.95P0.05O0.8F0.2 showed the structural transition temperature at 140K. It seems that there is a relation between the superconductivity and shrinkage of the crystal lattice. The flake type of grains was observed by SEM pictures of samples.

Effect of electric poling on structural, magnetic and ferroelectric properties of 0.8PbFe0.5Nb0.5O3-0.2BiFeO3 multiferroic solid solution

The effect of electric poling on structure, magnetic and ferroelectric properties of 0.8PbFe 0.5 Nb 0.5 O 3 -0.2BiFeO 3 (0.8PFN-0.2BFO) multiferroic was studied through XRD, Raman, magnetic and ferroelectric measurements. Single step solid state reaction method was adopted to synthesize single phase 0.8PFN-0.2BFO multiferroic at lower calcination and sintering temperature. Room temperature (RT) XRD pattern before and after poling confirmed the monoclinic structure with Cm space group. Rietveld refined XRD for poled and unpoled sample shows the influence of electric poling on Fe-O1, Fe-O2, Nb-O and Bi-O modes. There is a small variation in the lattice parameters after electric poling. The structural properties were also studied in detail for the poled and unpoled 0.8PFN-0.2BFO using Raman spectroscopy. Raman measurements were carried out over a wide range of temperature (250–550 K) for both poled and unpoled samples. At RT unpoled 0.8PFN-0.2BFO multiferroic exhibit 8 active modes at 211, 263, 440, 484, 571, 706, 785 and 1120 cm -1 in the frequency range 100–1200 cm -1 . The Raman peaks exhibits significant changes in intensity as well as shape of the spectra at the characteristic temperature T C (470 K) and T N (310 K). Poled Raman spectra show major changes in the Fe/Nb-O modes intensities around T N and are due to dynamic nature of spin phonon coupling. Changes observed in the temperature dependent magnetic measurements i.e. ZFC/FC and M − H loop evidence the existence of converse magneto-electric coupling (CME) and this is due to the poling effects on Fe-O, Nb-O active modes. Due to rotation of the oxygen octahedral the electric field induced strain will originate in the system. P-E loops after poling show an increase in remnant polarisation and coercive field due to an improvement in domain ordering. The potential tunability of magnetisation with electric poling is an ideal tool for realisation of application in practical devices.

Low Temperature Dielectric and Impedance Spectroscopy Studies of 0.9PFN - 0.1BFO Multiferroic Solid Solution

Single step solid state reaction method was adopted to synthesize 0.9PFN - 0.1BFO (PFN - BFO) multiferroic solid solution. Single phase was confirmed through X-Ray Diffraction (XRD) and the structural analysis from Rietveld refinement confirms the monoclinic structure with Cm space group. Temperature dependent dielectric constant and loss tangent shows an anomaly around Néel temperature (TN) at 240 K and is a clear signature of existence of indirect magnetoelectric coupling in the solid solution. The complex impedance spectroscopy exhibits a significant contribution from the grains and confirms the non Debye type nature. Bulk resistance decreases with increase in temperature shows negative temperature coefficient of resistance (NTCR) behavior. Electrical modulus spectra are of non Debye type. The ac and dc conductivity of the materials were found to increase with increase in temperature.

Impedance spectroscopy studies on PbFe0.5Nb0.5O3 –BiFeO3 multiferroic solid solution

(1-x) PbFe0.5Nb0.5O3 (PFN) – (x) BiFeO3 (BFO) (PFN – BFO) multiferroic solid solution (x = 0.1, 0.2, 0.3 and 0.4) were synthesized by single step solid state reaction method. Single phase was confirmed in all the samples through room temperature (RT) X-ray Diffraction (XRD) with monoclinic structure (Cm space group). Transmission Electron Microscopy (TEM) studies confirm the high crystallinity of the materials with the average particle size of 100nm. The temperature (313–528K) and frequency (100Hz – 5MHz) dependent impedance, modulus and DC conductivity of PFN – BFO solid solutions were investigated. An impedance spectroscopy result shows a significant contribution from the grains (bulk) to the conductivity and exhibits non-Debye type of relaxation. The bulk (grain) resistance reduces as the temperature increases corresponds to negative temperature coefficient of resistance (NTCR) behaviour. Electric modulus exhibits thermally dependent relaxation phenomena in the material. The Bergmann modified KWW function fitted to the imaginary modulus with non-Debye type of relaxation. DC conductivity of PFN – BFO solid solutions was found to follow the Arrhenius behaviour.

Structural, dielectric and conductivity studies of PbFe0.5Nb0.5O3 - BiFeO3 multiferroic solid solution

Single step solid state reaction method was adopted to synthesize (1-x) PbFe0.5Nb0.5O3 (PFN) - (x) BiFeO3 (BFO) (PFN - BFO) multiferroic solid solution with x = 0.1, 0.2, 0.3 and 0.4. Structural analysis of PFN - BFO solid solution was carried out by X Ray Diffraction (XRD) and confirmed the single phase in all solid solutions with negligible amount of pyrochlore (x = 0.2 and 0.4). The Rietveld refined XRD data was well fitted with monoclinic structure (Cm space group). The TEM analysis showed good crystallinity and the average particle size was found to be 100 nm. Dielectric constant (ε′), loss tangent (tan δ) and AC conductivity (σac) of PFN - BFO solid solution were carried out over a wide range of frequency (100 Hz–1 MHz) and temperature (303 K–600 K). The dielectric constant and loss tangent showed the temperature and frequency dependent nature in all solid solutions. The temperature dependent dielectric constant exhibits broad diffuse ferroelectric to paraelectric phase transition with systematic shift in ferroelectric to paraelectric transition temperature (TC). The TC value gets shifted to 423 K, 473 K, 523 K and 563 K for x = 0.1, 0.2, 0.3 and 0.4 respectively and was well supported by differential scanning calorimetric (DSC) measurements. Frequency dependent AC conductivity of PFN - BFO solid solution obeys Johnscher's power law and the conduction mechanism follows Correlated Barrier Hopping (CBH) model. AC conductivity exhibits negative temperature coefficient resistance (NTCR) kind of behaviour.

Structural, Magnetic and Dielectric Studies of Pb0.9Bi0.1Fe0.55Nb0.45O3 Multiferroic Solid solution

Single phase Pb0.9Bi0.1Fe0.55Nb0.45O3 (PFN-BFO) multiferroic solid solution was synthesized through single step solid state reaction method using low temperature annealing technique. The crystal structure, microstructure, magnetic and dielectric properties of PFN-BFO solid solution were investigated at room temperature (RT). Sintered samples were then subjected to XRD analysis and it revealed the formation of single phase without any impurities. The structural analysis was carried out by Rietveld Refinement technique through the Full Prof suite. The RT Rietveld refined XRD pattern confirms the monoclinic structure with Cm space group and obtained cell parameters are a = 5.666(3)A, b = 5.667(4)A, c = 4.017(2)A and p = 89.943(4)°. The surface morphology of the sample was studied by Scanning electron microscope (SEM) and average grain size was estimated to be ∼5μm. M-H curve shows the weak ferromagnetic kind of behaviour with antiferromagnetic ordering. Room temperature dielectric constant, loss tangent and impedance spectroscopic data were measured at different frequencies (100Hz - 5MHz). The impedance spectroscopy reveals the contribution from the grains towards the electrical parameters.

Effect of Sintering Temperature and Duration on the Formation of Single-Phase Pb0.9Bi0.1Fe0.55Nb0.45O3 Solid Solution

ABSTRACTEffect of sintering temperature and duration on single phase formation and structural properties of Pb0.9Bi0.1Fe0.55Nb0.45O3 (PBFNO) solid solution was investigated. The single step solid state reaction method was adopted to achieve the pure perovskite phase. Calcination was carried out at 700oC for 2 h and sintering at different temperatures as 800o, 850o, 900o, 950o, 1000o and 1050oC for 1 h and also at 800oC for 1-5 h to achieve the single phase in PBFNO solid solution. From the X-ray diffraction studies, it was found that sintering at 800oC for 3 h was optimum for achieving single phase and all the other conditions showed an impurity phase. Rietveld refinement was carried out on single phase PBFNO solid solution by using FullProf Suite, which confirmed the monoclinic structure with Cm space group and the obtained refinement parameters were Rp=15.7; Rw p=20.7, Rexp=16.72, χ2(Chi2)=1.54. The lattice parameters were: a=5.666(3) Å, b=5.667(4) Å, c=4.017(2) Å and α=γ=90o, β=89.943(4)o. Scanning electron micrograph showed an average grain size of ∼2 μm with uniform morphology. All the results clearly revealed the significance of low temperature and short duration sintering to control the single phase in PBFNO solid solution.

Determination of density of states, conduction mechanisms and dielectric properties of nickel disulfide nanoparticles

Temperature and frequency dependent ac electrical measurements were used to explore density of states, conduction mechanisms and dielectric properties of nickel disulfide (NiS2) nanoparticles. The NiS2 nanoparticles were prepared by conventional one step solid state reaction method at 250 °C. X-ray diffraction (XRD) confirmed cubic phase of prepared nanoparticles. Scanning electron microscope (SEM) images revealed presence of irregular shaped nanoparticles as small as 50 nm. The ac electrical measurements were carried out from 300 K to 413 K. Two depressed semicircular arcs from 20 Hz to 2 MHz showed presence of bulk and grain boundary phases in NiS2 nanoparticles at all temperatures. Small polaron hopping conduction from 300 K to 393 K and correlated barrier hopping conduction mechanism at temperatures higher than 393 K was observed. High value of density of states (of the order of 1024 eV−1cm−3) was calculated from ac conductivity. At low frequencies high values (of the order of 104-107) of real part of dielectric constant (ε′) were observed at different temperatures. These observations suggest that NiS2 nanoparticles may find applications in electronic devices.

Investigation on structural, Mössbauer and ferroelectric properties of (1−x)PbFe0.5Nb0.5O3–(x)BiFeO3 solid solution

In this study, (1−x)PbFe0.5Nb0.5O3(PFN)–(x)BiFeO3(BFO) multiferroic solid solutions with x=0.0, 0.1, 0.2, 0.3 and 0.4 were synthesized through single step solid state reaction method and characterized thoroughly through X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infra-Red (FTIR), Raman, Mössbauer spectroscopy and ferroelectric studies. The room temperature (RT) XRD studies confirmed the formation of single phase with negligible amount of secondary phases (x=0.2 and 0.4). The zoomed XRD patterns of (1−x)PFN–(x)BFO solid solutions showed the clear structural phase transition from monoclinic (Cm) to rhombohedral (R3c) at x=0.4. The Raman spectra of the (1−x)PFN–(x)BFO solid solutions showed the composition dependent phase transition from monoclinic (Cm) to rhombohedral (R3c). With increasing x in PFN, the modes related monoclinic symmetry changes to those of rhombohedral symmetry. The RT Mössbauer spectroscopy results evidenced the existence of composition dependent phase transition from paramagnetic to weak antiferromagnetic ordering and weak antiferromagnetic to antiferromagnetic ordering. The Mössbauer spectroscopy showed paramagnetic behavior with a doublet for x=0.0, 0.1 and 0.2 are shows the weak antiferromagnetic with paramagnetic ordering. For x=0.3 and 0.4 shows the sextet pattern and it is a clear evidence of antiferromagnetism. The ferroelectric (P–E) loops at RT indicate the presence of small polarization, as the x concentration increases in PFN, the remnant polarization and coercive field were decreased, which may due to the increase in the conductivity and leaky behavior of the samples.

Fabrication and microstructure of cerium doped lutetium aluminum garnet (Ce:LuAG) transparent ceramics by solid-state reaction method

Polycrystalline Ce3+ doped lutetium aluminum garnet (Ce:LuAG) transparent ceramics fabricated by one step solid-state reaction method using synthetic nano-sized Lu2O3, commercial α-Al2O3 and CeO2 powders were investigated in this paper. The green compacts shaped by the mixed powders were successfully densified into Ce:LuAG transparent ceramics after vacuum sintering at 1750°C for 10h. The in-line optical transmittance of the Ce:LuAG ceramic made by home-made Lu2O3 powders could reach 57.48% at 550nm, which was higher than that of the ceramic made by commercial Lu2O3 powders (22.96%). The microstructure observation showed that light scattering centers caused by micro-pores, aluminum segregation and refraction index inhomogeneities induced the decrease of optical transparency of the Ce:LuAG ceramics, which should be removed and optimized in the future work.

Low temperature magnetic studies on PbFe0.5Nb0.5O3 multiferroic

PbFe0.5Nb0.5O3 (PFN), a well-known A(B′1/2B″1/2)O3 type multiferroic, was successfully synthesized in single phase by a single step solid state reaction method. The single phase PFN was characterized through XRD, microstructure through SEM, and magnetic studies were carried out through a temperature dependent vibrating sample magnetometer (VSM) and neutron diffraction (ND) measurements. PFN exhibits a cusp at around 150K in the temperature dependent magnetic susceptibility corresponding to the Néel temperature (TN1) and another peak around 10K (TN2) corresponding to spin-glass like transition. In the temperature dependent ND studies, a magnetic Bragg peak appears at Q=1.35Å−1 (where Q=4πsinθ/λ, is called the scattering vector) below TN (150K) implying antiferromagnetic (AFM) ordering in the system. On the basis of Rietveld analysis of the ND data at T=2K, the magnetic structure of PFN could be explained by a G-type antiferromagnetic structure.

Structural and electrical studies on Zn 2+ doped LiCoPO 4

Zinc doped LiCoPO4 was prepared by two step solid state reaction method. XRD studies ensure the formation of phase pure LiCoPO4 with olivine phase orthorhombic structure with pnma phase group. 2θ value of XRD peaks of LiCoPO4 is found to be shifted upon Zn2+ doping. The conductivity of pure LiCoPO4 is noticed to be increased by one order upon doping of Zn2+. The scaling behavior of Z″ indicates that the ion dynamical process are temperature independent for both pure and Zn2+ doped LiCoPO4. The temperature dependence of conductivity for both pure and Zn2+ doped sample obeys Arrhenius law of conduction.

Mg-doped TlBa2(Ca2-xMgx)(Cu2.2Ti0.8)O10-δ (x = 0, 0.05, 0.15, 0.25, 0.35) superconductors

Ti-doped TlBa2(Ca2-xMgx)(Cu2.2Ti0.8)O10-δ (x = 0, 0.05, 0.15, 0.25, 0.35) samples are synthesized at 860 °C by two step solid state reaction method. All these samples have shown metallic variations of resistivity from room temperature down to onset of superconductivity. The room temperature resistivity systematically increases with increased Mg contents in the final compound. The onset temperature of superconductivity [Tc(onset)], as observed in the resistivity and susceptibility measurements, and the zero resistivity critical temperature are found to increase for Mg-doping of x = 0.05 and 0.15; however, the values of these parameters are suppressed for Mg-doping of x = 0.25 and 0.35. Magnitude of the superconductivity also increases for Mg-doping of x = 0.05 and 0.15, whereas its values decrease for Mg-doping of x = 0.25 and 0.35. All TlBa2(Ca2-xMgx)(Cu2.2Ti0.8)O10-δ (x = 0, 0.05, 0.15, 0.25, 0.35) samples have shown orthorhombic crystal structure and the c-axis lattice parameter is systematically suppressed with the increase of Mg-doping. In the phonon modes assignment as observed from Fourier transform infrared spectrometer absorption measurements, the planar oxygen mode is softened, whereas the apical oxygen mode of type Tl-OA-Cu(2)/Ti is hardened with increased Mg-doping. The Oδ mode of oxygen atoms increases in intensity with increased Mg incorporation in the final compound. It is most likely that the density of phonon modes increases till mg-doping of x = 0.15, but for x = 0.25 and 0.35 the c-axis length decreases further, which may enhance the population of an-harmonic modes of oscillations. Such competitive modes of oscillations are most likely produced due to the presence of two different masses existing in the conducting CuO2/TiO2 planes, i.e., Ti (47.90 amu) and Cu (63.54 amu). Since the distance between the planes decreases with increased Mg-doping, the equilibrium population of the phonon modes in CuO2/TiO2 planes may also change and hence the Tc and magnitude of superconductivity. These observations strongly suggest the existence of electron-phonon interactions essential for the mechanism of high Tc superconductivity.

Significant enhancement of the intergrain coupling in lightly F-doped SmFeAsO superconductors

A series of polycrystalline SmFeAsO1−xFx bulks (x = 0–0.25) were synthesized by a one step solid state reaction method at a low heat temperature of 900 ° C, which was about 300 ° C lower than the conventional temperature (∼1200 ° C). The magnetic susceptibility measurements showed single step superconducting transitions for the lightly doped samples with 0.05 ≤ x ≤ 0.12, while the double-step-like transitions were observed in samples x ≥ 0.15, indicating weak-link behavior of the grains. The double step transition is due to the possible occurrence of intergranular (at low temperature) and intragranular (near Tc) superconductivity consisting of coupled superconducting grains, and becomes broad with increasing x. The lightly doped samples with x = 0.10–0.12 have the onset Tc up to 51 K and the intergranular critical current density of over 103 A cm−2 at 5 K in self-field. This intergrain Jc value is one order of magnitude higher than the optimally doped samples (x = 0.2, Tc = 57 K), as assessed by remanent magnetization measurements. These results suggest strong intergrain coupling, and are expected to motivate future research and development for lightly fluorine-doped regions of REFeAs(O, F) superconductors.

Synthesis and structural characterization of Co2+ ions doped ZnO nanopowders by solid state reaction through sonication

Cobalt ions doped zinc oxide nanopowder was prepared at room temperature by a novel and simple one step solid-state reaction method through sonication in the presence of a suitable surfactant Sodium Lauryl Sulphate (SLS). The prepared powder was characterized by various spectroscopic techniques. Powder XRD data revealed that the crystal structure belongs to hexagonal and its average crystallite size was evaluated. From optical absorption data, crystal fields (Dq), inter-electronic repulsion parameters (B, C) were evaluated. By correlating optical and EPR spectral data, the site symmetry of Co2+ ion in the host lattice was determined as octahedral. Photoluminescence spectra exhibited the emission bands in ultraviolet and blue regions. The CIE chromaticity coordinates are also evaluated from the emission spectrum. FT-IR spectra showed the characteristic vibrational bands of ZnO.

Photoluminescence and photoconductivity studies of ZnO nanoparticles prepared by solid state reaction method

In the present work, the effect of annealing temperature on the luminescence and photoconductivity properties of ZnO nanoparticles (NPs) has been investigated. The ZnO NPs have been prepared at low temperature by a simple one step solid state reaction method using ZnSO4·7H2O as a starting precursor. X-ray diffraction results show, the prepared samples have a hexagonal wurtzite structure of ZnO NPs. FE-SEM reveals that the prepared ZnO nanoparticles have perfect spherical shape with little agglomeration. UV–visible absorption spectrum of as-prepared ZnO sample shows an absorbance peak at ~372 nm (~3.32 eV), which is blue shifted as compared to bulk ZnO (~386 nm). The annealed sample exhibits red shift of absorption peak. The photoluminescence spectra of as-prepared sample as well as annealed samples show one emission peak in UV region, and violet, blue, blue-green and green emissions in visible region. The sample annealed at 650 °C results in a significant reduction in luminescence as compared to that of the sample annealed at 450 °C. The photoconductivity properties such as voltage dependence of photocurrent, growth and decay of photocurrent as well as wavelength dependence of photocurrent have been studied in detail.

Superconductivity in CeO 1−xF xFeAs with upper critical field of 94 T

We have successfully synthesized Ce based oxypnictide superconductors with fluorine doping (CeO 1− x F x FeAs) by a two step solid state reaction method. Detailed XRD and EDX confirm the crystal structure and chemical compositions. We observe that an extremely high H c2(0) of 94 T can be achieved in the x = 0.1 composition. This increase in H c2(0) is accompanied by a decrease in transition temperature (38.4 K in x = 0.1 composition) from 42.5 K for the x = 0.2 phase. The in-plane Ginzburg–Landau coherence length is estimated to be ∼27 Å at x = 0.2 suggesting a moderate anisotropy in this class of superconductors. The Seebeck coefficient confirms the majority carrier to be electrons and strong dominance of electron–electron correlations in this multiband superconductor.

熱電変換材料 二段階固相反応法によるＢａｙＦｅｘＣｏ４−ｘＳｂ１２の合成および電気的性質

Filled skutterudite compounds, BayFexCo4-xSb12 (x=0-3.0, y=0-0.7), were synthesized by a two step solid state reaction method. Electrical transport properties of BayFexCo4-xSb12 were investigated. The lattice constants of BayFexCo4-xSb12 increased with increasing Ba filling fraction and Fe content. The maximum filling fraction of Ba (ymax) in BayFexCo4-xSb12 increased with increasing Fe content, and was found to be rather greater than that of CeyFex Co4-xSb12. The ymax, varied from 0.35 to near 1.0 when Fe content (x) changed from 0 to 4.0. Carrier concentration and electrical conductivity increased with increasing Fe content, and decreased with increasing Ba filling fraction for BayFexCo4-xSb12. At the same x and y, carrier concentration and electrical conductivity of BayFexCo4-xSb12 were larger than that of CeyFexCo4-xSb12.