Standard energies of combustion and standard enthalpies of formation for the complexes RE （Et2dtc）3（phen） （RE = Ho, Er, Tm, Yb, Lu）

The treatment of RECl3.xH2O （RE = Ho, Er, Tm, Yb, Lu; x = 3-4） with sodium diethyldithiocarbamate （NaEtEdtc-3H2O） and 1,10-phenanthroline hydrate （o-phen.H2O） in absolute ethanol yielded five ternary solid complexes RE（EtEdtC）a（phen）. IR spectra of the complexes showed that RE^3＋ coordinated to two sulfur atoms in NaEt2dtc and two nitrogen atoms in o-phen. The constant-volume energies of combustion of the complexes have been determined by a precise rotating-bomb calorimeter at 298.15 K. The standard enthalpies of combustion and standard enthalpies of formation were calculated.     

Crystal structure of R3Ge4 compounds (R Er, Ho, Tm, Lu)

The crystal structure of binary germanides R₃Ge₄ (R Er, Ho, Tm, Lu) has been determined by means of powder X-ray diffraction. For Er₃Ge₄ a full-structure determination has been performed using the Rietveld method (306 reflections, space group Cmcm,

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). The location of the atoms in Er₃Ge₄ is similar to that in the W₃CoB₃ structure, with the Ge atoms substituting for Co and B. For the other R₃Ge₄ compounds (RHo, Tm and Lu) the lattice parameters are given.     

Magnetic structures of R2RhSi3 (R=Ho, Er) compounds

Powder X-ray and neutron diffraction and magnetic measurements have been performed on R₂RhSi₃ (R=Ho and Er) compounds at low temperatures. The compounds crystallize in a derivative of the hexagonal AlB₂-type structure. The crystal structure parameters have been refined on the basis of the X-ray and neutron diffraction patterns collected in the paramagnetic region. These compounds are antiferromagnets with Néel temperatures of 5.2 K for Ho₂RhSi₃ and 5 K for Er₂RhSi₃. Both compounds exhibit collinear magnetic structures, described by the propagation vector k=(1/2,0,0) for Ho₂RhSi₃ and k=(0,0,0) for Er₂RhSi₃. This magnetic order is stable in the temperature range between 1.5 K and the Néel temperature.     

Magnetic ordering in ternary RMn2Ge2 compounds (R = Tb, Ho, Er, Tm, Lu) from neutron diffraction study

The compounds RMn₂Ge₂ (R = Tb, Ho, Er, Tm, Lu) have been investigated by neutron diffraction. TbMn₂Ge₂ is a collinear ferrimagnet with the Mn and Tb moment aligned along the c axis (μ_TB = 8.81(59) μ_B: μ_Mn = 2.21(44) μ_B). HoMn₂Ge₂ exhibits incommensurale ordering below 2.1 K characterized by two wavevectors at 1.3 K: q₁ = (0.1543(4), 0.1543(4), 0) and q₂ = (0.210(1), 0.007(1), 0). The Mn sublattice remains antiferromagnetic down to 1.3 K (μ_Mn = 2.38(6) μ_B). The Er moments order ferromagnetically below 5.5 K in ErMn₂Ge₂ (μ_Mn = 6.81(31) μ_B). The moments are perpendicular to the c axis. The Mn sublattice remains antiferromagnetic down to 1.8 K (μ_Mn = 2.34(18) μ_B). The magnetic structure of TmMn₂Ge₂ is characterized by the propagation vector (0.0.1/2). the Tm moments lying in the basal plane. The ordering of the Tm moments yields a canting of the Mn moments (τ = 21(3)°); μ_Tm = 6.63(18) μ_B; μ_Mn = 2.28(27) μ_B). The antiferromagnetic structure of LuMn₂Ge₂ has been determined (μ_Mn = 2.32(14) μ_B). The evolution of the magnetic properties of the heavy rare earth compounds RMn₂Ge₂ is discussed.     

The origin of the large magnetocaloric effect in RCo2 (R=Er, Ho and Dy)

The phase transitions of the RCo₂ (R=Er, Ho and Dy) compounds are of first-order type and a metamagnetic transition is observed above the Curie temperature. Owing to their large magnetic entropy change, the RCo₂ compounds are competitive candidates as the working substance for magnetic refrigeration. In this paper we discuss the origin of this large magnetic entropy change.     

Crystal structures of R2Pd2Pb (R = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) compounds

The crystal structures of the R₂Pd₂Pb (R=Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) compounds were determined using X-ray powder diffraction. The investigated compounds crystallize with Mo₂FeB₂ structure type (space group P4/mbm, Pearson code tP10). The importance of stabilization by polar intermetallic R–Pd bonding is underscored by a bonding analysis derived from electronic band structure calculations.     

The crystal structure of R10Co9In20 (R=Er, Tm, Lu) compounds

New ternary indides R₁₀Co₉In₂₀ (R=Er, Tm, Lu) have been found in the systems {Er, Tm, Lu}–Co–In at 870 K. The crystal structure of Tm₁₀Co₉In₂₀ has been refined using single-crystal X-ray data: Ho₁₀Ni₉In₂₀ structure type, P4/nmm space group, Z=2, a=13.166(5) Å, c=9.097(4) Å, V=1577(2) ų, R=0.0315 for 335 unique reflections hkl (DARTCH-1 diffractometer, MoK_α radiation). The coordination polyhedra of the Tm atoms have 16 and 17 vertices, those of the In atoms 12 and 13 vertices and those of the Co atoms 8 and 10 vertices. The structure can be described as a stacking of polyhedra formed by In atoms.     

Large reversible magnetocaloric effect in the RECoC2 (RE=Ho and Er) compounds

The crystal structure, magnetic properties and magnetocaloric effect (MCE) of HoCoC₂ and ErCoC₂ have been investigated. They both crystallize in orthorhombic CeNiC₂-type structure with Amm2 space group and a second-order paramagnetic to ferromagnetic phase transition around the Curie temperature T_C ∼11 K and ∼14 K occurred in them. Under the magnetic field change (ΔH) of 0–5 T, the maximal values of magnetic entropy change, refrigerant capacity and relative cooling power are 15.6 J/kg K, 183 J/kg, 242 J/kg for HoCoC₂ and 17.2 J/kg K, 243 J/kg, 375 J/kg for ErCoC₂, respectively.     

Thermal decomposition products of heteronuclear Cu---Re complexes, CuRE(dhbaen)(NO3)·nH2O (RE---La, Eu, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb, and Lu)

To facilitate the preparation of finer and more homogeneous CuREO_x and to achieve a lowering of the formation temperature, heteronuclear CuRE(1:1) complexes, CuRE(dhbaen)(NO₃)·nH₂O were synthesized as precursor. As it was expected for RE=La through Gd, only a mixture of CuO and CuRE₂O₄ was formed even when the complex decomposed at 800 °C since the Cu/RE ratio is 1. For RE=Y and Tb through Lu, Cu₂RE₂O₅ was formed by way of CuO and RE₂O₃. The structure of the decomposed product is controlled by the coordination number and ionic size of RE ion. The minimum radius ratio for eightfold coordination of RE³⁺ ion suggests that preparation of homogeneous Cu:RE(1:1) oxide with Cu₂Ho₂O₅ type structure is difficult for RE=La through Gd.     

Irradiation-induced amorphized state of rapidly quenched R 12Fe82B6 alloys (R = Nd, Er)

Rapidly quenched (RQ) alloys R ₁₂Fe₈₂B₆ (R = Nd, Er) have been prepared by melt spinning. Their magnetic properties, structure, and phase composition have been studied before and after fast-neutron irradiation to a fluence of 1.2 × 10²⁰ n/cm². Before irradiation, it is the Nd₂Fe₁₄B-type phase (space group P4₂/mnm) that is mainly present in the RQ alloys at 295 K. In the Nd₁₂Fe₈₂B₆ alloy, this phase has a ferro-magnetic structure with magnetic moments at the Nd and Fe atoms oriented parallel to the c axis; the Er₂Fe₁₄B phase found in the Er₁₂Fe₈₂B₆ alloy is characterized by a ferrimagnetic order of Er and Fe magnetic moments parallel to the basal plane. After irradiation, the crystalline state of both RQ alloys transforms into an amorphous state. The ferro- and ferrimagnetic orders are retained in them, but the Curie temperature of the alloys with Nd and Er decreases by 100 and 200 K, respectively. The spontaneous magnetization of the irradiated alloys at 5 K is approximately equal to their magnetization in the crystalline state, whereas their coercive force is lower than that for the alloys before irradiation by two orders of magnitude. The effects observed are explained by the dispersion of Fe-Fe exchange interactions resulting from the dispersion of interatomic spacings in the amorphous alloys.     

White luminescence of Ho3+/Tm3+/Yb3+-codoped CaWO4 synthesized via citrate complex route assisted by microwave irradiation

The nanocrystalline Ho³⁺/Tm³⁺/Yb³⁺ co-doped CaWO₄ upconversion (UC) phosphors were successfully synthesized by a modified citrate complex method using microwave irradiation. The citrate complex precursors were heat-treated at temperature ranging from 300 to 700 °C for 3 h. Crystallization of the Ho³⁺/Tm³⁺/Yb³⁺ co-doped CaWO₄ was detected at 400 °C, and entirely completed at 600 °C. The Ho³⁺/Tm³⁺/Yb³⁺ co-doped CaWO₄ heat-treated at 600 °C showed primarily spherical and homogeneous morphology. Under the laser excitation of 980 nm, Ho³⁺/Tm³⁺/Yb³⁺ co-doped CaWO₄ shows the bright white upconversion (UC) emission visible to the naked eye, which is composed of a blue emission at 475 nm from Tm³⁺, and green and red emissions at 543 and 651 nm respectively from Ho³⁺. The coordinates of Ho³⁺/Tm³⁺/Yb³⁺ co-doped CaWO₄ in the Commission International De'eclairage (CIE) chromaticity diagram could be controlled from a cool to a warm white color depending on the Tm³⁺ and Ho³⁺ concentrations. The UC luminescent properties on Tm³⁺ and Ho³⁺ concentrations and related mechanism based on laser pump power were discussed in detail.     

溶胶-凝胶合成Er3 和Ho3 离子掺杂的Gd2(MoO4)3上转换发光纳米晶

采用柠檬酸与乙二醇溶胶-凝胶法合成了Er3 和Ho3 离子分别掺杂的铝酸钆Gd2(MoO4)3纳米晶.用XRD证实了产物的结构,用扫描电镜与透射电镜研究了产物微观形貌与尺寸.在980nm激光泵浦下,Ho3 掺杂Gd2(MoO4)3纳米晶发出很强的位于660nm的红光,而Er3 掺杂Gd2(MoO4)3纳米晶发出很强的位于540nm左右的红光.共掺Yb3 分别对Ho3 与Er3 起着显著的敏化作用.从发光强度与激光功率变化图中可知,Ho3 与Er3 的发光均属于双子光发光过程.     

Substitutional effects in RFe3 intermetallics (R=Dy,Sm, Y)

Samples of RFe₃ (R=Dy, Sm, Y) were doped with Si, Al and Ti and studied by Mössbauer spectroscopy and X-ray diffraction. Most Mössbauer spectra were analyzed with three sextets, corresponding to the 6c, 3b and 18 h inequivalent lattice sites for iron. A quadrupole split doublet was also present in some spectra, which became dominant for the case of Al substitution. The collapse of the hyperfine magnetic structure is a magnetic effect due to substitutions: the X-ray diffraction patterns yielded a particle size of about 100 nm, thus precluding the occurrence of superparamagnetism in these systems.     

Magnetic anisotropy and magnetic properties of RTSi (R=Gd, Y; T=Mn, Fe) compounds

Magnetic properties of Gd_xY_1−xMnSi and GdMn_xFe_1−xSi compounds with CeFeSi-type structure have been studied by magnetization measurements in the temperature range 77–600 K in static magnetic fields up to 12 kOe. The measurements for some compounds have been carried out on single crystal samples. The easy magnetization direction of all single crystal samples was found to be the c axis. The value of the anisotropy constant K₁ for GdMnSi was estimated to be 2.0·10⁶ erg cm⁻³ at 77 K. The substitution in both rare earth and 3d sublattices leads to a sharp increase in magnetic anisotropy of these compounds. The concentration dependencies of magnetic ordering temperatures, effective magnetic moments and paramagnetic Curie temperatures have been determined. The obtained results can be explained by the modification of the band structure due to the change of interatomic distances and the filling of 3d band.     

Crystal structure of new ternary RE1.9Cu9.2Sn2.8 compounds (RE = Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu)

A series of isotypic RE_1.9Cu_9.2Sn_2.8 compounds, where RE are Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, was synthesized by arc-melting and the crystal structure was determined by X-ray powder diffraction. The structure is a partly disordered substitution variant of the CeNi₅Sn structure type (space group P6₃/mmc), which consists of CaCu₅-type fragments of composition RE_0.9Cu_4.2Sn_0.8 and fragments of a hypothetical structure of composition RECu₅Sn₂. All the RE_1.9Cu_9.2Sn_2.8 compounds obtained here are paramagnets and characterized by metal-like conductivity.     

A study on microstructure and luminescent properties of oxyfluoride silicate glass-ceramics with (Ho,Yb):NaYF4 crystallites

Glass-ceramics containing NaYF₄ nanocrystals were prepared by heat-treatment from oxyfluoride silicate-based glass doped with Ho³⁺ and Yb³⁺ ions. The formation of crystalline fluoride phase was confirmed by X-ray diffraction and transmission electron microscopy. Absorption and emission spectra revealed that a fraction of Ho³⁺ and Yb³⁺ ions is incorporated into the NaYF₄ ordered lattice influencing spectroscopic features of glass-ceramics in comparison with those of precursor glass. Green up-conversion emission (545 nm) originating in the ⁵S₂ level in glass-ceramics and up-converted red emission (650 nm) originating in the ⁵F₅ level in as-melted glass were observed under optical pumping into Yb³⁺ absorption band and analyzed. Although both emissions in both materials are achieved by two-photon excitations, the relation between green and red emission intensity in glass-ceramics and glass implies that processes relevant to up-conversion phenomena are different. Based on a careful analysis of relaxation dynamics of Ho³⁺ and Yb³⁺ excited states, the mechanisms involved in conversion of the infrared radiation into the visible emission in these materials are proposed and discussed.     

MAGNETIC PROPERTIES OF R 3(Fe, Mo) 29 N x (R=Sm OR Y) INTERSTITIAL NITRIDES

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New TiNiSi-type RMgAg and RMgPd with R=Ca, Yb, and MgZn2-type Ca(Mg,Ag)2 compounds

The phases CaMgAg, YbMgAg, CaMgPd, and YbMgPd were synthesized by melting the constituent metals in sealed tantalum crucibles and by annealing at 1023 K. All the samples were homogeneous, and the crystallographic analysis, which was performed by powder and singlecrystal techniques, shows that the four compounds are isotypic and belong to the orthorhombic TiNiSi type. Magnetic measurements showed that YbMgAg and YbMgPd behave like Pauli paramagnets, according to the divalency of Yb in both phases. Within the Ca-Mg-Ag system, the existence range of the MgZn₂-type phases in the Mg-rich CaMg_2−x Ag _x pseudobinary system goes from CaMg₂ to CaMg_1.6Ag_0.4. Another stability region of the MgZn₂ structure occurs around the Ag-rich composition (Ca_0.94Mg_0.06)(Ag_1.60Mg_0.40), where magnesium replaces both the Ca and Ag atoms.