INVESTIGATION OF THE PHOTOELECTRONIC PROPERTIES OF RARE-EARTH MONOPHOSPHIDES

The optical, electrical and photoelectronic properties of rare earth monophosphides (LnP, Ln = La, Nd, Sm and Y) have been studied. The experimental results indicate that their resistivities are low, the electric conduction in all of them is N-type, the energy gaps of LaP, NdP, SmP and YP are 1.46eV, 1.15eV, 1.1eV and 1.0eV, respectively. The SmP/Si and YP/Si junctions exhibit the photovoltaic effect. They may be used as photoelectronic sensors.

THE PHOTOELECTRIC PROPERTIES OF THIN-FILMS OF RARE-EARTH MONOPHOSPHIDES

The optical, electrical and photoelectric properties of rare earth monophosphides (LnP, Ln = La, Nd, Sm, Y, Dy and Yb) have been studied in thin films. The films exhibit semiconducting behaviour with energy gaps of 1.0-1.46 eV and n-type electrical conduction. Their resistivities are 10(-2) OMEGA-cm with corresponding Hall mobilities of 8.5-400 cm2 V-1 s-1. The films are deposited on a p-type silicon substrate in vacuum. Voltage-current characteristic measurements show that a p-n junction has been formed between LnP and silicon. Spectral sensitivity and a photovoltaic effect have been observed in LnP-Si junctions. They may be useful photoelectric materials.

STUDY ON RARE EARTH-HEDTA-SERINE TERNARY SYSTEM BY POTENTIOMETRY AND FLUORESCENCE SPECTROSCOPY

In this pare earth-HEDTA-serine (Ser) ternary system has been studied by potentiometric titration at 25 degrees C with an ionic strength of 0.15 mol.L-1 (NaCl). The excitation and fluorescence spectra of TbCl3, Tb-Ser, Tb-HEDTA and Tb-HEDTA-Ser have hem determined at room temperature. The stability constants of these ternary complexes have been obtained, It lieu been found that Tb-HEDTA-Ser ternary system exhibit characteriatic fluorescence spectrum of Tb3+ sensitized by two ligands,The results mean that the chemical hood between the control ion and the ligand in this ternary system is predominantly ionic in character,and the energy transfer from ligand to Tb8+ is performed by a kind of abort-range electron exchange action.

THERMODYNAMICS OF COMPLEXATION OF RARE EARTHS BY L-METHIONINE

The protonation constant of the ligand and stability constants of it complexes with rare earths have been determined by potentiometric titration at 25 degrees C and ionic strength mu=0.15 mol - L-1. The results indicate that rare earth elements can form 1:1 complexes with L methionine. There is an apparent "tetrad effect" in this system. Shift of the yttrium position to the vicinity of Gd can he explained by the different polarisation between the Ln(3+) and the ligand. The enthalpy changed (Lambda H-101) of the coordination reaction as represented by the reaction (M + L (sic) ML) here been measured by calorimetric titration, where M and L. denote are eartus and L-Mer respectively. The Lambda G(101) and Delta S-101 of these reaction have been calculated by using Gibbs' equation, Furthermore, the stability of rare earth complexes with L-Met has been compared with that of Ca3+ Zn3+, Fe2+, Fe3+ complexes with L-Met.

XPS STUDY ON RARE-EARTH PHTHALOCYANINE COMPLEXES

The rare earth monophthalocyanine complexes, LnPcCl and LnPc(OAc)2 (Ln = Tb, Ho, Tm, Lu, Pc=Phthalocyanine, OAc = Acetate), were synthesized. The electronic structures of the complexes have been studied by means of XPS. The experimental results of binding energies for the complexes indicate that the bonds of the complexes have a certain covalent character depending on L-->Ln charge transfer. This L-->Ln charge transfer process of phythalocyanine complexes differs from that of crown ether complexes. Both coordination and substitution are included in the former case, but only coordination in the latter. Phthalocyanine ring is an electrophilic group and its electronegativity is large. So, the O1s binding energies of coordinating oxygen atoms of acetate in LnPc(OAc)2 are larger than those of Ln(OAc)3. The magnitude of valent charge delocalized from ligand onto metal atom is dependent on electronegativity, coordination number, valence state and so on. Because coordination number of Ln in LnPc(OAc)2 is larger than that in LnPcCl and electronegativity of Clin LnPcCl is larger than that of O in LnPc(OAc)2, the Ln4d5/2 binding energies of LnPc (OAc)2 are less than those of LnPcCl.

DIELS-ALDER REACTION CATALYZED BY RARE-EARTH CHLORIDES

Rare earth chlorides were used to catalyze the synthesis of 2-butoxy-3, 4-dihydro-2H-pyran using equimolar acrolein and vinyl butyl either. The cycloadduct is unstable which undergoes catalytic ring opening oligomerization. The way to stabilize the cyclo adduct has been studied, thus high yields of 90-95% were obtained.

DETERMINATION OF TRACE AMOUNT OF 14 RARE-EARTH IMPURITIES IN HIGH-PURITY YTTRIUM-OXIDE WITH ICP-AES

A method of analysis of high purity yttrium oxide with ICP-AES was described with emphasis on the study of Y_2O_3 matrix effects. The results showed that the line intensities of ana]ytes decreased with the increase of Y_2O_3 concentration in solution because of following factors. (1) The presence of matrix resulted in the decrease of the amount of analytes reaching ICP. (2) Matrix Y_2O_3 entering the plasma decreased the excitation temperature of the plasma and depressed the ionization of analytes in the pl...

STUDY OF BIMETALLIC COMPLEXES OF RARE-EARTH LITHIUM - SYNTHESIS AND CRYSTAL-STRUCTURE OF THE (LACL)DME(MU-2-CL)5(MU-3-CL) (LA.DME)LI(THF)2

The reaction between LaCl_3 and LiCl in THF at room temperature, with hexane as precipitant and glycol dimethyl ether as complexing agent, has been studied. A complex with the composition of (LaCl)DME(μ_2-Cl)_5(μ_3-Cl)(La·DME)Li(THF)_2 has been synthesized, its structure was studied by single crystal X-ray diffraction technique. The diffraction intensities were collected at about —100℃. The complex belongs to the triclinic space group P1 with α=11.123(3), 6=16.564(5), c=8.653(3)A, α=95.16(3), β=...

SYNTHESIS AND CRYSTAL-STRUCTURES OF THE BIMETALLIC RARE-EARTH COMPLEXES AND STUDIES ON INSERTION MECHANISM OF DIENES POLYMERIZATION

The deepening of the studies on essentials of rare earth coordination catalyst brings about more and more reports on model compounds as active centre of the catalyst. Among them the most significant researches are those with identification of the crystal structures of compounds.

SYNTHESIS AND VIBRATIONAL SPECTRUM STUDIES OF RARE EARTH COMPLEXES WITH CYCLOHEXANE CARBOXYLIC ACID

The solid state complexes of trivalent lanthanid, yttrium and scandium with cyclohexane carboxylic acid have been isolated and characterized by IR and Raman spectroscopy. It was found that there are only chelated carboxylate groups in the scandium complex and that there are the chelated, bridged and chelate-bridged carboxylate groups in other rare earth complexes. The former is a mononuclear complex and the latter is a polynuclear polymer. The RE—O coordinate bonds possess the characters of convalent ionic ...

Study on the concentration and seasonal variation of inorganic elements in 35 species of marine algae

The concentrations of five major and 28 trace elements in 35 marine algae collected along the coast of China were determined by instrumental neutron activation analysis. The concentrations of halogens, rare earth elements and many transition metal elements in marine algae are remarkably higher than those in terrestrial plants. The concentration factors for 31 elements in all collected algae were calculated, those for tri- and tetra-valent elements were higher than those of the mono- and di-valent elements in marine algae. The biogeochemical characteristics of inorganic elements in marine algae were investigated. In addition, the seasonal variation of inorganic elements in Sargassum kjellmanianum was also studied. (C) 1998 Elsevier Science B.V. All rights reserved.

Genesis of Th-230 excess in basalts from mid-ocean ridges and ocean islands: Constraints from the global U-series isotope database and major and rare earth element geochemistry

Based on Th-230-U-238 disequilibrium and major element data from mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs), this study calculates mantle melting parameters, and thereby investigates the origin of Th-230 excess. (Th-230/U-238) in global MORBs shows a positive correlation with Fe-8, P (o), Na-8, and F-melt (Fe-8 and Na-8 are FeO and Na2O contents respectively after correction for crustal fractionation relative to MgO = 8 wt%, P (o)=pressure of initial melting and F (melt)=degree of melt), while Th-230 excess in OIBs has no obvious correlation with either initial mantle melting depth or the average degree of mantle melting. Furthermore, compared with the MORBs, higher (Th-230/U-238) in OIBs actually corresponds to a lower melting degree. This suggests that the Th-230 excess in MORBs is controlled by mantle melting conditions, while the Th-230 excess in OIBs is more likely related to the deep garnet control. The vast majority of calculated initial melting pressures of MORBs with excess Th-230 are between 1.0 and 2.5 GPa, which is consistent with the conclusion from experiments in recent years that D (U)> D (Th) for Al-clinopyroxene at pressures of > 1.0 GPa. The initial melting pressure of OIBs is 2.2-3.5 GPa (around the spinel-garnet transition zone), with their low excess Ra-226 compared to MORBs also suggesting a deeper mantle source. Accordingly, excess Th-230 in MORBs and OIBs may be formed respectively in the spinel and garnet stability field. In addition, there is no obvious correlation of K2O/TiO2 with (Th-230/U-238) and initial melting pressure (P (o)) of MORBs, so it is proposed that the melting depth producing excess Th-230 does not tap the spinel-garnet transition zone. OIBs and MORBs in both (Th-230/U-238) vs. K2O/TiO2 and (Th-230/U-238) vs. P (o) plots fall in two distinct areas, indicating that the mineral phases which dominate their excess Th-230 are different. Ce/Yb-Ce curves of fast and slow ridge MORBs are similar, while, in comparison, the Ce/Yb-Ce curve for OIBs shows more influence from garnet. The mechanisms generating excess Th-230 in MORBs and OIBs are significantly different, with formation of excess Th-230 in the garnet zone only being suitable for OIBs.

Determination of multiple trace elements in seawater using chelation ion chromatography and ICP-MS

An off-line chelation system combined with ICP-MS technique was developed for the quantitative determination of trace elements in seawater, namely V, Co, Ni, Cu, Zn, Mo, Cd, Pb, U and rare earth elements(REEs). The system was built based on an ion chromatography equipped with MetPac((R)) CC-I chelation columns which had a strong selective chelation to these target elements within a pH range 5.2-5.6. Acidified seawater samples and NH4Ac(2 mol/L) were blended to meet suitable pH before being injected into the chelation column, thus target elements were retained while alkali and alkaline metals were excluded. Then chelated elements were eluted by HNO3 (1 mol/L) and samples were collected for ICP-MS analysis. Varying the ratio of input( gen. 200 mL) to output( gen. 5 mL), the target elements which were concentrated as 40 times as their concentrations were far beyond instrumental quantification limits. At last, a certificated seawater CASS-4 was introduced and our detected values were in good agreement with those certified values.