Synthesis and properties of Ba3NaRu2O9−δ and Ba3(Na, R)Ru2O9−δ (R=rare earth) crystals

Crystals of Ba₃NaRu₂O_9−δ (δ≈0.5) and Ba₃(Na, R)Ru₂O_9−δ (R=Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb) were grown by an electrochemical method, and their crystallographic, magnetic, and electric properties were studied. All crystals have a hexagonal structure of space group P6₃mmc. Ba₃NaRu₂O_9−δ and Ba₃(Na, R)Ru₂O_9−δ (except Ce) have a negative asymptotic Curie temperature suggesting the existence of an antiferromagnetic order; however, they are paramagnetic at temperatures above 1.7 K. Ba₃NaRu₂O_9−δ has an effective magnetic moment P_eff of 0.91 μ_B, while P_eff of Ba₃(Na, R)Ru₂O_9−δ (except Ce) reflects the large free-ion moment of the rare earth ions. Ba₃(Na, Ce)Ru₂O_9−δ shows peculiar magnetic behavior that differs from the magnetism of other Ba₃(Na, R)Ru₂O_9−δ crystals. The resistivity of all crystals exhibits an activation-type temperature dependence with an activation energy in the range of 0.10.2 eV.     

Paramagnetic susceptibility simulations from crystal field effects on rare earth antimonates R3Sb5O12

The magnetic susceptibilities of polycrystalline rare earth antimonates R₃Sb₅O₁₂ (R=rare earth), with cubic structure, space group I43m (No. 217), where the point site symmetry of R is S₄, have been measured from 4.2 to 800 K. Using the wave functions and energy levels derived from standard free ion and crystal field parameters deduced from the analysis of the optical spectra of pure and/or doped Pr, Nd, Eu and Er compounds, the calculation of the temperature dependent paramagnetic susceptibility has been carried out according to the Van Vleck formalism. The same calculation through crystal field parameters resulting from the ab initio simple overlap model over the entire R₃Sb₅O₁₂ series has been performed. Curves of both kinds were very similar for each configuration, with the exception of those for the Pr compound. Very good agreements with experimental data are found, especially below around 400 K, even when the approximate D_2d (near S₄) potential is considered. The standard crystal field treatment of 4f^N configurations is shown to explain the magnetic properties of these compounds with no need to consider any sort of magnetic interaction between the magnetic ions.     

The effect of f-ion valence on superconductivity in the series Pb2Sr2RCu3O8 (R=Ce, Pr, Tb and Am)

The magnetic properties and valences of the rare earth ions are probed in the superconducting series Pb₂Sr₂R_1−xCa_xCu₃O₈ (R=Ce, Pr, Tb and Am). The R=Pr and Tb samples are superconducting for x≈0.5 below 61 and 72 K, respectively, whereas the Ce and Am samples could not be made superconducting for any single phase sample, irrespective of x. X-ray absorption near edge spectroscopy (XANES), used to probe the valence of R, reveals that Pr and Tb are trivalent whereas the Ce and Am are tetravalent. This direct correlation of R valence and the observation of superconductivity is discussed.     

Studies on the interaction between lanthanide ions and ligands, in solid complexes of lanthanide hexacyanometalates. Part II. The kinetics of thermal dehydration of lanthanide hexacyanocobaltate (III) hydrates, Ln[Co(CN)6]·nH2O and yttrium hexacyanocobaltate (III) tetrahydrates

Series complexes of lanthanide hexacyanocobaltates (III), Ln[Co(CN)₆]·nH₂O (Ln=lanthanide ions; n=5,4) and yttrium hexacyanocobaltates (III) tetrahydrate were prepared, and the kinetics of the thermal dehydrations of these hydrates was studied. The dehydrations of Ln[Co(CN)₆]·5H₂O (Ln=La to Nd) took place through at least three stages, and those of Ln[Co(CN)₆]·4H₂O (Ln=Ce to Lu, and Y) through at least two stages. The each dehydration stage was found to be described as a first order reaction, F₁. Activation energy for each stage was determined on the basis of thermogravimetry. The relationship between the activation energy for the each dehydration stages and the thermal stability of the series hydrates which was changing with the decrease of the ionic radii of lanthanide ions, was discussed.     

Ternary RPt4B (R=La, Ce, Pr, Nd) compounds; structural and physical characterisation

The compounds RPt₄B, with (R=La, Ce, Pr, Nd), were synthesized and their crystal structure was studied either by single crystal X-ray diffraction and/or by conventional and synchrotron X-ray powder diffraction. All four compounds of this family are isostructural and belong to the CeCo₄B structure type. AC-susceptibility and magnetization studies show that: there is no magnetic ordering of the La compound down to 1.7 K; the Ce compound presents an antiferromagnetic-type-transition at 2.4 K; and both Pr and Nd compounds present a ferromagnetic-type transition at 4.2 and 4.9 K, respectively. Electrical resistivity studies show metallic behaviour for all compounds, the temperature dependence for the La compound being described by the Bloch Gruneisen relation. Thermopower studies as a function of temperature show that the thermopower is positive and small for these compounds, which is consistent with hole dominated metallic behaviour.     

On rubidium lanthanide double chromates

Synthesis and crystallographic data are reported for a family of double rubidium-rare earth chromates RbLn(CrO₄)₂, where LnLa---Lu, Y and Sc. The compounds are closely related to the potassium chromates KLn(CrO₄)₂ but with a slightly different distribution of structural types: those of La, Pr and Nd are monoclinic, Sm, Eu, Gd are orthorhombic and those of Tb-Lu are also monoclinic but with another unit cell. RbSc(CrO₄)₂ has high and low temperature forms: hexagonal and monoclinic respectively. Lattice parameters of all the above compounds are given. Thermal decomposition takes place over 450 °C leading to the rare earth chromites and Cr₂O₃.     

New DySrAlO4 Compound Synthesis and Formation Process Correlations for LnSrAlO4 (Ln 5 Nd,Gd, Dy) Series

For the first time, DySrAlO₄ of K2NiF₄-type structure was synthesized. The parameters of DySrAlO4 elementary unit cell are determined as follows: a = 0.368 (4) nm, c = 1.229 (2) nm, V = 0.166 (4) nm³. The research of the complex aluminates LnSrAlO4 (Ln = Nd, Gd, Dy) solid-state process demonstrated the change of the formation mechanism among LnSrAlO₄ (Ln = Nd, Gd, Dy) series from DySrAlO₄ oxide. The performed analysis provided a possibility to realize why chemists couldn’t get DySrAlO₄ for a long period of time.     

Photoelectrochemical study of lanthanide titanium oxides, Ln2Ti2O7 (Ln = La, Sm, and Gd)

Photocatalytic activities for hydrogen evolution of lanthanide titanium oxides, Ln₂Ti₂O₇ (Ln = La, Pr, Nd, Sm, Gd, Dy, Ho, Er, and Yb) prepared by a solid-state reaction were studied. Hydrogen gas was clearly evolved in distilled water suspension of La₂Ti₂O₇ and Sm₂Ti₂O₇. From the photoelectrochemical measurements, the values of the flat band potential were estimated to be −0.04, −0.02, +0.27 eV for La₂Ti₂O₇, Sm₂Ti₂O₇, Gd₂Ti₂O₇, respectively, versus the normal hydrogen electrode (NHE). The values of the band gap energy were calculated to be about 3.29, 2.79, 2.82 eV for La₂Ti₂O₇, Sm₂Ti₂O₇, Gd₂Ti₂O₇, respectively. The photocatalytic activities of Ln₂Ti₂O₇ (La, Sm, and Gd) were discussed along with detailed band structures estimated in this study. From the band structures, Sm₂Ti₂O₇ is a possible candidate of photocatalyst responding to visible light.     

Comparison of the spectroscopic behaviour of single crystals of lanthanide halides (X = Cl, Br)

Halides belong to large band gap matrices that have the perspective of wide applications when doped by optical active ions. This paper presents the results of spectroscopic studies of single crystals of halides (Cl, Br) of Ce, Pr and Nd. Their spectroscopic behaviour: electron–phonon coupling, ion pair interactions and the effect of covalency, is compared. Absorption, emission and emission excitation spectra of single crystals of LnCl₃·yH₂O (Ln = Nd, Pr, Ce; y=6, 7) were recorded at room temperatures and low temperatures down to 4.2 K. The intensities of the electronic lines and the Judd–Ofelt parameters were calculated (Nd, Pr) and compared to those of LnBr₃·yH₂O presented earlier by us. The relationship between the hypersensitivity and covalency was discussed. With increasing soft character of the halides (Br⁻ > Cl⁻), the covalent character of Ln–ligand bond increases and the hypersensitive bands become more intense. The Judd–Ofelt intensity analysis resulted in a set of τ_λ parameters evaluated with quite low standard deviations. The temperature dependences of the intensities have been found and the vibronic coupling in the f–f transitions were analysed. At the low temperature (4.2 K), strong vibronic components occur in the electronic lines of the Nd(III) and Pr(III) ions, mainly with the Ln–X vibrations. The modes, which are in resonance with the splitting of the ground state multiplet, mediate in the cooperative transitions.

Vibrational studies of the compounds under test were performed at the ambient temperature using IR and Raman spectroscopy. The assignment of the bands was done on the basis of the factor group analysis. The spectral features below 300 cm⁻¹ point at the differences between the spectra of the bromides and chlorides of Nd and Pr. Although the spectral features within the FIR region are complex, the bands of the praseodymium monocrystals originated by halogen bridges are clearly visible.     

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.     

Optical study of a new phase LaGa3O6:RE (RE=Pr, Nd, Eu) in the La2O3–Ga2O3 system

The absorption and emission spectroscopies of RE³⁺ ions embedded in a new phase, LaGa₃O₆, owing to the La₂O₃–Ga₂O₃ binary system (RE=Pr, Nd, Eu) are discussed. The ^2S+1L_J level degeneracies are completely lifted in accordance with the low point symmetry of the site occupied by the rare earth ion in LaGa₃O₆. The energy level schemes deduced from the data are reproduced by considering a crystal field (CF) effective Hamiltonian involving the nine real and five imaginary parameters required for the C₂ or C_s symmetry of the rare earth site. The rms deviation is satisfactory for the three simulations. However, the strong variation of the CF parameters between Pr³⁺ and Eu³⁺ in LaGa₃O₆ suggests the possible limit of existence of the phase, intimately correlated to small variations of the rare earth ionic radius.     

Crystal structure and physical properties of ternary compounds RPt3B, R=La, Pr, Nd

The crystal structure of a new series of ternary rare-earth platinum borides RPt₃B (R=La, Pr, Nd) has been studied by X-ray powder diffraction analyses from the ‘as-cast’ alloys. The tetragonal CePt₃B structure type, space group P4mm (No. 99), has been confirmed for all compounds. Rietveld refinements for the two compounds, PrPt₃B and NdPt₃B, were performed. LaPt₃B is a temperature-independent Pauli-type paramagnet from room temperature down to 4 K. PrPt₃B orders antiferromagnetically at T_N=15 K followed by a ferromagnetic spin flip at T_C=5 K, whereas NdPt₃B exhibits an antiferromagnetic spin alignment at a Néel temperature T_N=7 K. The temperature dependence of the electrical resistivity, ρ(T), reflects the metallic character of these compounds. Furthermore the characteristic changes of slope of ρ(T) plots prove the magnetic transitions.     

Photoelectrochemical study of lanthanide zirconium oxides, Ln2Zr2O7 (Ln = La, Ce, Nd and Sm)

Photocatalytic activities for hydrogen evolution of lanthanide zirconium oxides, Ln₂Zr₂O₇ (Ln = La, Ce, Nd and Sm) prepared by a solution reaction method were investigated. Under the illumination of 500 W Xenon lamps, hydrogen gas was clearly evolved in a distilled water suspension of La₂Zr₂O₇, Sm₂Zr₂O₇ and Nd₂Zr₂O₇. Under the visible-light illumination, hydrogen gas was evolved in a distilled water suspension of Nd₂Zr₂O₇ and Sm₂Zr₂O₇. From the photoelectrochemical measurements, the values of the flat band potential were estimated to be −0.64, −0.52, −0.31 and +0.04 eV for La₂Zr₂O₇, Sm₂Zr₂O₇, Nd₂Zr₂O₇ and Ce₂Zr₂O₇, respectively, versus the normal hydrogen electrode (NHE). The values of the band gap energy were calculated to be about 3.52, 2.86, 2.67 and 2.53 eV for La₂Zr₂O₇, Sm₂Zr₂O₇, Nd₂Zr₂O₇ and Ce₂Zr₂O₇, respectively. Due to the effect of 4f orbital electrons, the band gap energy of these compounds becomes narrower than in ZrO₂ and as a consequence, Sm₂Zr₂O₇ and Nd₂Zr₂O₇ show the photocatalytic activity under the visible-light.     

A contribution to the crystallochemistry of ternary 1:1:1 and 1:1:2 rare earth intermetallic phases with Pb and Pd

The ternary alloys of the rare earths with lead and palladium were studied for the stoichiometric ratios 1:1:1 and 1:1:2 with respect to the structure of these alloys and their existence field. RPbPd (R = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb) compounds have a hexagonal structure, hP9 Fe₂P type, while RPbPd₂ (R = Pr, Sm, Gd, Tb, Dy, Ho, Er, Yb) alloys have the cubic AlCu₂Mn-type structure (cF16, BiF₃ superstructure).     

Subsolidus phase relation and crystal structure of the PrBa2−xSrxCu3O7±δ system

The PrBa_2−xSr_xCu₃O_7±δ solid solution was investigated by means of X-ray powder diffraction in combination with Rietveld analysis. The Sr-doped Pr123 single phase could be synthesized at 950 °C in air. The solubility of PrBa_2−xSr_xCu₃O_7±δ solid solution is 0.2≤x≤0.6. The structure of PrBa_2−xSr_xCu₃O_7±δ is orthorhombic for x=0.2. The structure transforms into tetragonal for 0.3≤x≤0.6. In the PrBa_2−xSr_xCu₃O_7±δ structure, Sr ions can replace Ba ions, the highest value is x=0.6 under our experimental condition. But Sr ions could not replace Pr ions. Furthermore Pr ions could not occupy the sites of Ba ions in the PrBa_2−xSr_xCu₃O_7±δ system. Both ionic radii and chemical properties play an important role in the mutual substitution of Pr, Ba and Sr ions in the Pr123 structure of the PrBa_2−xSr_xCu₃O_7±δ system.     

Synthesis and magnetic properties of R2Co17Nx type interstitial compounds

A series of interstitial ternary nitrides R₂Co₁₇N_x with 1.6 ≤ x ≤ 2.7 was prepared, with R Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Y. The nitrides have the same structures as the parent compounds, i.e. the Th₂Zn₁₇ or Th₂Ni₁₇ type, but the unit-cell volumes are about 6% larger. The Co magnetic moment and the R---Co coupling strength are found to be reduced by the nitrogenation. The diffusion of nitrogen in the R₂Co₁₇ compounds is remarkably slower than in R₂Fe₁₇. Decomposition of all R₂Co₁₇N_x compounds is found to start above 870 K.     

Spectroscopy, magnetism and non-radiative processes in heteronuclear Cu:Pr squarate; [Pr2Cu(C4O4)4(H2O)16]·2H2O

In the present work, the spectroscopic and magnetic properties of heteronuclear Cu:Pr squarate are reported. Single crystals of [Pr₂Cu(C₄O₄)₄(H₂O)₁₆]·2H₂O were obtained by reaction of squaric acid, praseodymium chloride and copper chloride in water solution according to the procedure described earlier. The crystals of title compound are isomorphic with [La₂Cu(C₄O₄)₄(H₂O)₁₆]·2H₂O crystal, where squarate anions participate as bridging ligands between metal ions.

The UV region of absorption spectra of the title compound is dominated by C–T band of Cu(II), f–d transition of Pr(III) and internal π–π*(A_1g→E_u) and π–π*(A_1g→E_g) ligand transitions. In visible and IR regions, t_2g–e_g of copper Cu(II) as well as ³H₄→³P_J, ¹D₂, ¹G₄, ³F_J, ³H₆ Pr(III) transitions at 293 and 4 K were recorded. At low temperature splitting given by Jahn–Teller effect can be observed. Significant anisotropy of d–d transitions intensities confirms well the Jahn–Teller effect, too. Unexpectedly high intensity of ³H₄→¹G₄ transition is probably due to the intensity borrowing from the Cu (II) d–d transition.

The ³P₀ and ¹D₂ emission of Pr(III) in the [Pr₂Cu(C₄O₄)₄(H₂O)₁₆]·2H₂O crystals is quenched even at 77 K. Whereas emission of appropriate polynuclear europium squarate was detected. The pathways of excited state quenching by e_g levels of Cu(II), multhiphonon relaxation and concentration quenching can be considered in the system under studies. Magnetic susceptibility measurements were carried out in 300–1.7 K temperature range and are discussed in relation to the structure.

Effect of the polymeric structure on spectroscopic behaviour is presented. Selectivity of polymeric europium squarate in vitro test for different tumor cells is shown.     

Comparative magnetic studies of (Sm, Nd) trichloroacetates and their heteronuclear CuLn2(CCl3COO)8·6H2O systems: structure and spectroscopy of a new type of Eu trichloroacetate

Two series of compounds: heteronuclear CuLn₂(CCl₃COO)₈·6H₂O (Ln = Nd and Sm) and their simple analogues Ln(CCl₃COO)₃·2H₂O (Ln = Eu, Nd, Sm) were synthesized. New Eu(III) trichloroacetate; Eu(CCl₃COO)₃·3H₂O·CH₃OH was obtained, its molecular structure was determined by X-ray diffraction and compared with the data of respective systems reported earlier. Magnetization was measured and the susceptibility was derived in the limit of low field. Magnetic susceptibilities were calculated and discussed for series of homo- and hetero-nuclear chloroacetates.

Untypical hysteresis was found (two loops) in samarium trichloroacetate. This phenomenon is most probably the effect of flops of spins in magnetic fields of 30,000 Oe and very weak (if any) interaction intermediated by weak hydrogen bonding between the chains. A similar magnetic behavior was observed in neodymium carboxylate where the magnetic ordering was observed as a result of Nd–Nd interaction at low temperature (1.6 K). For this system, the magnetic moment depends on magnitude of the magnetic field and ferromagnetic ordering appears at low temperatures. The strongest interactions of coupled ions and antiferromagnetic ordering with T_N=6.5 K were found in CuSm₂(CCl₃COO)₈·6H₂O single crystals.

Heisenberg model was applied in the calculations for three interacting ions located linearly. The following relation was derived:

and applied in calculations of the exchange integrals. Mechanism of the exchange interaction was discussed on the basis of the obtained results.     

New low thermal expansion ceramics: Sintering and thermal behavior of Ln1/3Zr2(PO4)3-based composites

Materials with the general formula M_xZr₂(PO₄)₃ are known to possess low coefficients of thermal expansion (CTE). The present work investigates the thermal properties of new composite materials issued from the decomposition at high temperature of Ln_1/3Zr₂(PO₄)₃ (Ln=La, Gd). The decomposition process was studied and showed that the resulting powder was a LnPO₄, Zr₂P₂O₉ and ZrO₂ mixture. Composite materials made of that mixture were sintered and characterized. The effect of sintering aids such as ZnO was considered. Final densities of the composites were about 90% of theoretical density and these materials presented low CTE in the 10⁻⁶ °C⁻¹ range.     

Thermal and structural properties of KPO3·Ln(PO3)3 glasses (Ln=rare earth ion)

Glass transition temperatures T_g and Raman spectra of KPO₃·Ln(PO₃)₃ (Ln=rare earth ion) glasses were measured for all rare earth members (except Pm). From the series behavior of the T_g and Raman data, it is concluded that the coordination number around rare earth ions changes, probably from nine to eight, in the middle of the rare earth series.