Atomic ordering in the doped rare earth cobaltates Ln0.33Sr0.67CoO3−δ (Ln=Y, Ho and Dy)

The perovskite-based rare earth cobaltates (Ln_0.33Sr_0.67CoO_3−δ) (Ln=Y³⁺, Ho³⁺ and Dy³⁺) have been synthesized at 1100°C under 1 atm oxygen. A thermogravimetric study has determined the overall oxygen content in each case while a combined electron diffraction (ED) and synchrotron X-ray diffraction study has revealed the presence of a complex, previously unreported, perovskite-related superstructure phase. ED gave a resultant C1c1 but most probably Cmcm (, , ) perovskite-related superstructure, describable as a modulated I4/mmm intermediate parent structure. Synchrotron X-ray data has been used to refine the intermediate parent structures of all three compounds. Coupled Ln/Sr and O/vacancy ordering and associated structural relaxation is shown to be responsible for the observed superstructure.     

Сrystal structure and physical properties of the new ternary antimonides Ln3Pd8Sb4 (Ln=Y, Gd, Tb, Dy, Ho, Er, Tm)

The ternary antimonides Ln₃Pd₈Sb₄ (Ln=Y, Gd, Tb, Dy, Ho, Er, Tm) have been synthesized for the first time. The crystal structure of Er₃Pd₈Sb₄ has been solved from the X-ray single crystal data: own type structure, space group Fm3¯m, a=1.3050(1) nm, R_F=0.0484, R_W=0.0524 for 17 free parameters and 401 reflections with F(hkl)>4σ(F). The structure of Er₃Pd₈Sb₄ can be viewed as a ternary ordered version of the Sc₁₁Ir₄-type. The lattice parameters of the isotypic compounds Ln₃Pd₈Sb₄ (Ln=Y, Gd, Tb, Dy, Ho, Tm) have been refined from the X-ray powder diffraction data. The magnetic and electrical properties of the compounds Ln₃Pd₈Sb₄ (Ln=Tb, Ho, Er) have been studied down to 1.75 K. The Ho- and Er-based phases have been found to order antiferromagnetically at 2.5 and 2.0 K, respectively. For all three compounds, the magnetic susceptibility follows in the paramagnetic region the Curie-Weiss behavior with the effective magnetic moments close to the respective free trivalent ion values. All three antimonides studied exhibit metallic character of the electrical conductivity.     

Conductivity and carrier traps in La1−xSrxCo1−zMnzO3−δ (x=0.3; z=0 and 0.25)

Measurements of the equilibrium oxygen content, electrical conductivity and thermopower in the perovskite-like solid solution La_0.7Sr_0.3Co_1-zMn_zO_3−δ (z=0 and 0.25) as a function of the temperature and oxygen partial pressure are used to determine the temperature dependence of the conductivity and thermopower at different values of the oxygen deficiency. A model for a hopping conductor with screened charge disproportionation is applied for the data analysis in combination with trapping reactions of n- and p-type carriers on local oxygen vacancy clusters and manganese cations, respectively. Changes in the ratio of n-type to p-type mobility are due to variations in oxygen vacancy concentration and manganese content, while the energetic parameters governing charge disproportionation of the trivalent cobalt cations and formation of vacancy associates are shown to be essentially invariable. These calculated charge carrier site occupancies are used to model temperature variations of the electrical properties in La_0.7Sr_0.3Co_1−zMn_zO_3−δ in favorable correspondence with experimental observations.     

Ab Initio Study on The Influence of Spin State upon Bonding and Interaction in Fe-COBondCovalenciesinR2BaCuO5(R=Sm,Gd,Dy,Ho,Y,Er,Tm,Yb,Lu)

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The synthesis, crystal chemistry and structures of Y-doped brannerite (U1−xYxTi2O6) and thorutite (Th1−xYxTi2O6−δ) phases

Yttrium-doped uranium brannerite (U_1−xY_xTi₂O₆) and thorutite (Th_1−xY_xTi₂O_6−δ) phases were synthesized in air at 1400°C. Powder X-ray diffraction revealed that these phases crystallized to form monoclinic (C2/m) structures. Crystal structures of U_0.54Y_0.46Ti₂O₆ (1) (a=9.8008(2); b=3.7276(1); c=6.8745(1); β=118.38(1); V=220.97(1); Z=2; R_P=7.3%; R_B=4.6%) and Th_0.91Y_0.09Ti₂O_6−δ (2) (a=9.8002(7); b=3.7510(3); c=6.9990(5); β=118.37(4); V=226.40(3); Z=2; R_P=4.5%; R_B=2.9%) were refined from powder neutron diffraction data. These two phases were isostructural, revealing planes of corner and edge-sharing TiO₆ octahedra separated by irregular eight-fold coordinate U/Y or Th/Y atoms. The oxygen sites within the structure of 1 were found to be fully occupied, confirming that the doping of lower valence Y atoms occurs in conjunction with the oxidation of U(IV) to U(V). Y doping of the thorutite phase 2 does not lead to oxidation but rather the formation of oxygen vacancies within the structure.     

Über die verbreitung ternärer komplexnitride mit Perowskitstruktur in SE-Al-N-systemen (SE ≡ La,Ce, Pr,Nd, Sm,Gd, Tb,Dy, Ho,Er, Tm,Yb, Lu)

The existence of complex nitrides in the RE-Al-N (RE ≡ rare earth) ternaries is investigated. In the systems containing lanthanum, cerium, praseodymium, neodymium and samarium either ternary phases (RE)₃AlN_x with a perovskite-type structure or alternatively almost complete filling of the octahedral voids by nitrogen in (RE)₃Al phases with an L1₂-type structure are found. An isothermal section for Pr-Al-N at 600 °C is presented. In the systems RE-A1-N (RE ≡ Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) no ternary phase is observed.     

Synthesis and magnetism of rare earth (Nd,Gd,Dy,Ho,Er,Y) pentafluoropropionate binuclear complexes with 2-(4''''-methoxy-phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide

Six compounds of the general formula [Ln(pfpr)3]2(NITPhOMe).nH2O, where Ln=Nd, Gd, Dy, Ho, Er, Y, pfpr=pentafluoropropionate, NITPhOMe=2-(4'-methoxyphenyl)-4,4,5, 5-tetra-methylimidazoline-1-oxyl-3-oxide, and n=4 (for Nd, Dy, Er); 3 (for Gd); 6 (for Ho); 5 (for Y), have been synthesized. These complexes were characterized by elemental analyses, IR, electronic spectra and molar conductances. The variable temperature (4-300 K) magnetic susceptibility of the complex [Gd(pfpr)3]2(NITPhOMe).3H2O was determined. The observed susceptibility data were fit to those from theoretical magnetic equation by least-squares method. The exchange integral, J, was found to be equal to 2.14 cm-1. This indicates a weak ferromagnetic spin-exchange interaction between the radical and the gadolinium(III) ion.     

Stability and oxygen ionic conductivity of zircon-type Ce1−xAxVO4+δ (A=Ca, Sr)

Zircon-type Ce_1−xA_xVO_4+δ (A=Ca, Sr; x=0-0.2) are stable in air up to approximately 1300 K, whilst further heating or reducing oxygen partial pressure leads to formation of A-site deficient zircon and CeO_2−δ phases. The stability boundaries of Ce_1−xA_xVO_4+δ are comparable to those of vanadium dioxide and calcium orthovanadate. At oxygen pressures lower than 10⁻¹⁵ atm, perovskite-type CeVO_3−δ is formed. The oxygen ion transference numbers of Ce_1−xA_xVO_4+δ, determined by faradaic efficiency measurements in air, vary in the range from 2×10⁻⁴ to 6×10⁻³ at 973-1223 K, increasing with temperature. The oxygen ionic conductivity has activation energy of 87-112 kJ/mol and is essentially independent of A-site dopant content. Contrary to the ionic transport, p-type electronic conductivity and Seebeck coefficient of Ce_1−xA_xVO_4+δ are influenced by the divalent cation concentration. The average thermal expansion coefficients of Ce_1−xA_xVO_4+δ, calculated from high-temperature XRD and dilatometric data in air, are (4.7-6.1)×10⁻⁶ K⁻¹.     

Syntheses, structure, and luminescent properties of novel hydrated rare earth borates Ln2B6O10OH4•H2O (Ln = Pr, Nd, Sm, Eu, Gd, Dy, Ho, and Y)

Ln(2)B(6)O(10)(OH)(4)?H(2)O (Ln = Pr, Nd, Sm-Gd, Dy, Ho, and Y), a new series of hydrated rare earth borates, have been synthesized under hydrothermal conditions. A single crystal of Nd analogue was used for the structure determination by X-ray diffraction. It crystallizes in the monoclinic space group C2/c with lattice constants a = 21.756(4), b = 4.3671(9), c = 12.192(2) ?, and β = 108.29(3)°. The other compounds are isostructural to Nd(2)B(6)O(10)(OH)(4)?H(2)O. The fundamental building block (FBB) of the polyborate anion in this structure is a three-membered ring [B(3)O(6)(OH)(2)](5-). The FBBs are connected by sharing oxygen atoms forming an infinite [B(3)O(5)(OH)(2)](3-) chain, and the chains are linked by hydrogen bonds, establishing a two-dimensional (2-D) [B(6)O(10)(OH)(4)?H(2)O](6-) layer. The 2-D borate layers are thus interconnected by Ln(3+) ions to form the complex three-dimensional structure. Ln(2)B(6)O(10)(OH)(4)?H(2)O dehydrates stepwise, giving rise to two new intermediate compounds Ln(2)B(6)O(10)(OH)(4) and Ln(2)B(6)O(11)(OH)(2). The investigation on the luminescent properties of Gd(2-2x)Eu(2x)B(6)O(10)(OH)(4)?H(2)O (x = 0.01-1.00) shows a high efficiency of Eu(3+) f-f transitions and the existence of the energy transfer process from Gd(3+) to Eu(3+). Eu(2)B(6)O(10)(OH)(4)?H(2)O and its two dehydrated products, Eu(2)B(6)O(10)(OH)(4) and Eu(2)B(6)O(11)(OH)(2), present the strongest emission peak at 620 nm ((5)D(0) → (7)F(2) transition), which may be potential red phosphors.     

Novel rare-earth borosilicide RE1−xB12Si3.3−δ (RE=Y, Gd-Lu) (0?x?0.5, δ≈0.3): synthesis, crystal growth, structure analysis and properties

New rare-earth boron-rich compounds with the formula of RE_1−xB₁₂Si_3.3−δ (RE=Y, Gd-Lu) (0?x?0.5,δ≈0.3) have been synthesized. They belong to a new type of rhombohedral structure with the space group of R-3m (No. 166) and z=9. The lattice constants were measured from powder XRD data. Crystal structure solved from powder XRD data for Tb_0.68B₁₂Si₃ as a representative has been compared with that of YB_17.6Si_4.6 (or Y_0.68B₁₂Si_3.01), whose structure was solved from single-crystal reflection data. The structure model is confirmed by high-resolution transmission microscope analysis. The vibrational modes of the new crystals were measured by Raman spectroscopy. Temperature dependence of magnetic susceptibility which was measured for RE_1−xB₁₂Si_3.3−δ single crystals by SQUID revealed that they are paramagnetic materials down to 2.0 K.     

RBa2Cu4O8(R=Dy,Ho,Er,Tm,Yb)和Y2Ba4Cu7O14.3的化学键参数计算

使用复杂晶体上化学键理论计算了RBa     

Study of the formation temperature of mixed LaREO<Subscript>3</Subscript> (RE ≡ Dy,Ho, Er,Tm, Yb,Lu) and NdGdO<Subscript>3</Subscript> oxides

Mixed LaREO₃ (RE ≡ Dy, Ho, Er, Tm, Yb, Lu) and NdGdO₃ oxides were prepared by thermal decomposition of the corresponding co-precipitated mixed oxalates. The decomposition of La/RE and Nd/Gd oxalates was studied by means of differential thermal analysis and thermogravimetric (DTA-TG) measurements; in particular the last step, consisting of the loss of a CO₂ molecule from the corresponding oxycarbonate, has been thoroughly investigated, as it is particularly interesting for the study of the formation temperature of mixed rare earth oxides. After the release of CO₂, the oxides crystallize in a distorted perovskitic cell or one of the structures typical of rare earth sesquioxides, depending on the cationic size difference and on the average cationic radius. The mixed rare earth oxycarbonate decomposition has been studied in comparison to the decomposition of single rare earth oxycarbonates. A trend of the mixed oxides formation temperature as a function both of the average cationic size and of the cationic sizes difference has been observed and compared to the behaviour of single rare earth oxides.     

M_2RSbO_6:R′~(3+)(M=Ba,Sr,Ca;R=La,Gd,Y,Bi;R′=Sm,Eu,Dy,Ho,Er,Tm)复合氧化物的合成,组成,结构和荧光性质

本文按文献的方法合成了Ba-2BiSbO_6,Ba_2GdSbO_6、M_2RSbO_6(M=Ba,Sr,Ca,R=La,Y),以M_2RSbO_6为基质掺Sm~(3+)、En~(3+)、Dy~(3+)、Ho~(3+)、Er~(3+)、Tm~(3+)、Bi~(3+)研究它们的化学组成,晶体结构与发光性能的关系及规律,Bi~(3+)的荧光及敏化作用,同时研究了它们     

Synthesis and characterization of the K2NiF4 phases La1+xSr1−xCo0.5Fe0.5O4−δ (x=0, 0.2)

The K₂NiF₄ phases LaSrCo_0.5Fe_0.5O₄ and La_1.2Sr_0.8Co_0.5Fe_0.5O₄, and their reduced forms LaSrCo_0.5Fe_0.5O_3.75 and La_1.2Sr_0.8Co_0.5Fe_0.5O_3.85, have been successfully prepared by solid-state reactions, followed by reduction in 10% H₂/N₂ in order to produce oxygen-deficient materials. All materials crystallize in a tetragonal K₂NiF₄ structure (space group I4/mmm) with Co and Fe randomly distributed over the B-sites of the structure. Mössbauer spectra have confirmed the trivalent state of Fe in these materials. In the reduced materials, oxide ion vacancies are confined to the equatorial planes of the K₂NiF₄ structure and the Co is present almost entirely as Co²⁺ ions; low-temperature neutron powder diffraction data reveal that these reduced phases are antiferromagnetically ordered with a tetragonal noncollinear arrangement of the moments. The Co³⁺ ions, present in stoichiometric LaSrCo_0.5Fe_0.5O₄ and La_1.2Sr_0.8Co_0.5Fe_0.5O₄, inhibit magnetic order and are assumed to be in the low-spin state.     

KCl-NaCl(1:1mol)-RECl_3熔体的电导率(RE=La、Ce、Pr、Nd、Sm、Eu、Gd、Tb、Dy、Ho、Er、Tm、Yb、Lu、Y、Ce族、Y族)

用交流电桥法测定了熔融KCl-NaCl(1:1摩尔)-RECl_3的电导。比电导的温度函数表达式如下: k=A+B(t-700) k:比电导(Ω~(-1)·cm~(-1));t:温度(700—850℃); A、B:本文给出的常数。 讨沦了实验值与计算值的偏差,当稀土氯化物在熔体中的浓度为10—50重量百分数时可能形成了络合物。     

KCl-NaCl(1:1mol)-RECl3熔体的电导率(RE=La、Ce、Pr、Nd、Sm、Eu、Gd、Tb、Dy、Ho、Er、Tm、Yb、Lu、Y、Ce族、Y族)

用交流电桥法测定了熔融KCl-NaCl(1:1摩尔)-RECl₃的电导。比电导的温度函数表达式如下: κ=A+B(t-700) κ:比电导(Ω^-1·cm^-1);t:温度(700—850℃); A、B:本文给出的常数。讨沦了实验值与计算值的偏差,当稀土氯化物在熔体中的浓度为10—50重量百分数时可能形成了络合物。     

The systems Zr(Nb,Ti)(R)O2−δ, R=Yb, Ca—optimization of mixed conductivity and comparison with results of other systems (R=Y and Gd)

In this work we address the optimization of mixed conductivity in fluorite compounds based on zirconia. Phase relations of the new systems YbO_1.5-NbO_2.5-ZrO₂, and CaO-NbO_2.5-ZrO₂ are presented. The limit of the cubic defect fluorite phase in YbO_1.5-NbO_2.5-ZrO₂ closely resembles that of the system YO_1.5-NbO_2.5-ZrO₂, whilst in CaO-NbO_2.5-ZrO₂ is narrow extending to include composition Ca_0.255Nb_0.15Zr_0.595O_1.82 at 1500°C. The influence of dopant ion size, charge and composition on ionic conduction is assessed and parallels are drawn with the systems YO_1.5-NbO_2.5-ZrO₂ and YO_1.5-TiO₂-ZrO₂. Comparison of these results with published data on the Ti containing systems CaO-TiO₂-ZrO₂, GdO_1.5-TiO₂-ZrO₂ shows that the highest mixed conducting compositions can only be offered in the system YO_1.5-TiO₂-ZrO₂ out of all the systems here studied.     

Powder Neutron Diffraction and TEM Investigations of Bi0.775Ln0.225O1.5 Oxide Conductors (Ln=La, Pr, Nd, Sm, Tb, Dy) with Rhombohedral Bi-Sr-O type: Structural Relationships with Monoclinic ε-Bi4.86La1.14O9 Form

Structural investigations of Bi_0.775Ln_0.225O_1.5 phases with rhombohedral Bi-Sr-O type, have been carried out using complementary techniques. Average crystal structures were refined from neutron diffraction powder data using the Rietveld method for Ln=La, Pr, Nd and Tb. The comparison with the monoclinic Bi_4.86La_1.14O₉ structure previously determined using the same technique has been done. For both types of structure, a piling of slabs constituted of a (Bi₍₁₎, Ln) oxide layer, inserted between two Bi₍₂₎ oxide layers, is observed. In the rhombohedral phases there are moreover oxide ions in the inter-slab spaces responsible for the well-known conductivity of these phases, while in the monoclinic Bi_4.86La_1.14O₉ structure, the absence of oxygen in the inter-slab spaces, is compensated with the presence of the Bi₍₂₎ lone pair electrons localized at a significant distance (≅1.20 Å), which participate in the cohesion of the crystal structure. TEM study of Bi_0.775Ln_0.225O_1.5 samples, has confirmed the existence of superstructures for these phases and has allowed to propose two types (respectively for La and for Nd, Sm, Tb or Dy) of q₁^* and q₂^* modulation wave vectors.     

Structural features of phases (Na<Subscript>0.5</Subscript>R<Subscript>0.5</Subscript>)MO<Subscript>4</Subscript> and (Na<Subscript>0.5</Subscript>R<Subscript>0.5</Subscript>)MO<Subscript>4</Subscript>:R′ (R = Gd,La; R′ = Er,Tm, Yb; M = W,Mo) of the scheelite family

The structural data for single crystals of (Na_0.5R_0.5)MO₄ and (Na_0.5R_0.5)MO₄:R′ (R = La, Gd; R′ = Er, Tm, Yb; M = W, Mo) grown by the Czochralski method were studied by X-ray diffraction and analyzed. The structural characteristics of these compounds depend on the sort of cations M and R. The formation of superstructures was found in the scheelite structure, and distortion of the scheelite structure depending on the composition and preparation conditions was established (with unit cell rotation by 45° and triclinic distortion of the scheelite structure for (Na_0.5Gd_0.5)WO₄:Tm, with doubled unit cell compared to the scheelite type structure for (Na_0.5Gd_0.5)WO₄ and (Na_0.5Gd_0.5)WO₄:Yb). In the case of overstoichiometric oxygen content in the crystal, the unit cell symmetry increases to space group I4₁/amd or (Na_0.5Gd_0.5)WO₄:Yb without considerable change in the cell parameters. On the basis of experimental data, a transformation scheme for the structures in the system Na ₂ ⁺ M⁶⁺O_4?-“R³⁺M⁵⁺O₄” was proposed.