Synthesis and characterization of decanuclear Ln(III) cluster of mixed calix[8]arene-phosphonate ligands (Ln = Pr,Nd)

Two novel decanuclear Ln(III) compounds (Ln = Pr for 1, Nd for 2) have been solvothermally obtained by using p-tert-butylcalix[8]arene (H₈TBC8A) and phenylphosphonate (PhPO₃H₂) as ligands. Single crystal X-ray diffraction studies reveal that both compounds are stacked by dumbbell-like Ln₁₀ clusters, which are capped by two TBC8A^8 − supports and linked by four complementary PhPO₃^2 − ligands as well as other bridging anions. In addition, the self-assembly behavior of both compounds is interesting: the cationic Ln₁₀ cluster layers are separated by the layers of H₆TBC8A^2 − ligands. Moreover, the luminescent and magnetic properties of both compounds were examined.     

Structure and dielectric properties of Ln3NbO7 (Ln = Nd,Gd, Dy,Er, Yb and Y)

The structure and dielectric properties of Ln₃NbO₇ (Ln = Nd, Gd, Dy, Er, Yb and Y) ceramics are investigated. With decreasing ionic radius of Ln³⁺, the stable crystal structure of the compounds shifts from orthorhombic weberite to defect fluorite. It is experimentally observed that, with the exception of Gd₃NbO₇, the room temperature real part of the relative permittivity of Ln₃NbO₇ ceramics decreases from approximately 40 to 30 (at 1 MHz) with increasing ionic radius of Ln³⁺. The observed imaginary part of the relative permittivity is in order of 10⁻² to 10⁻¹ (room temperature and 1 MHz) and it is relatively stable up to 80 °C, where it increases with a rise in temperature. Interesting exceptions of these trends are Nd₃NbO₇ that crystallizes with a weberite-type structure and shows large positive temperature variation of the dielectric properties, and Gd₃NbO₇ that crystallized in a weberite related structure and displays frequency and temperature dependent dielectric relaxation behavior.     

Near-infrared (NIR) luminescent homoleptic linear tetranuclear [Ln4((OH)2-Salophen)4] (Ln = Nd or Yb) complexes self-assembled from the dihydroxylated Salophen ligand

Through self-assembly of the (OH)₂-Salophen H₄L (H₄L = N, N′-bis(3-hydroxyl salicylidene)benzene-1,2-diamine) with LnCl₃·6H₂O (Ln = La, Nd, Yb, Er or Gd), series of [Ln₄((OH)₂-Salophen)₄]-arrayed complexes [Ln₄(H₂L)₂(L)₂(EtOH)₂] (Ln = La, 1; Ln = Nd, 2; Ln = Yb, 3; Ln = Er, 4 or Ln = Gd, 5) were obtained, respectively. The result of their photophysical properties shows that the strong and characteristic NIR luminescence for complexes 2–3 with emissive lifetimes in microsecond ranges is observed, and the sensitization arises from the excited state (¹LC) of the (OH)₂-Salophen ligand despite the luminescent quenching with OH-oscillators around the Ln^3 + ions.     

Near-infrared luminescent properties of Ln:LaGdZr2O7 (Ln = Nd,Yb) transparent ceramics for solid-state laser applications

Via a facile solid reactive method, transparent Ln_0.1La_0.9GdZr₂O₇ (Ln = Nd, Yb) ceramics were successfully fabricated for the first time. The highest in-line transmittances of Nd:LaGdZr₂O₇ and Yb:LaGdZr₂O₇ ceramics reached 68% and 69%, respectively, at 1100 nm. The microstructure and crystal structure of Ln_0.1La_0.9GdZr₂O₇ transparent ceramics were fully investigated, indicating that the solid reactive technique is a good method of industrially fabricating Ln_0.1La_0.9GdZr₂O₇ transparent ceramics. The PL spectra demonstrated that Ln_0.1La_0.9GdZr₂O₇ ceramics can effectively be excited at 808 nm and 976 nm, which correlates with the widely applied output wavelengths of AlGaAs and InGaAs laser diodes. The luminescence decay curves were also studied, showing that the average fluorescence lifetimes of Nd_0.1La_0.9GdZr₂O₇ and Yb_0.1La_0.9GdZr₂O₇ transparent ceramics was 355 μs and 663 μs, respectively. Combined with its high temperature resistance and good mechanical strength, Ln_0.1La_0.9GdZr₂O₇ (Ln = Nd, Yb) transparent ceramics can have potential applications in Nd/Yb solid-state laser construction.     

The dependence of lattice thermal conductivity on phonon modes in pyrochlore-related Ln2Sn2O7 (Ln = La,Gd)

Rare-earth pyrochlore materials are promising thermal barrier coatings materials and fundamental understanding of their thermal transport is crucial for further improving its performance. In this work, using density functional theory (DFT) method, we calculated the intrinsic lattice thermal conductivities of Ln₂Sn₂O₇ (Ln = La, Gd) and conducted a comprehensive analysis on the mode thermal conductivity, relaxation time, Grüneisen parameters, group velocity, and specific heat, respectively. It is shown that in pyrochlore-type materials the number of the optical phonons is much larger than that of the acoustic phonon, and the thermal conductivity of acoustic phonons are suppressed, both of which increase the contribution ratio of optical phonons. Especially, through cumulative analysis, we found that the contribution of optical phonons is significant: the ratio of optical contribution is more than 50% and 64% in La₂Sn₂O₇ and Gd₂Sn₂O₇. This work provides a comprehensive picture illustrating the significant role of the optical phonons in the lattice thermal conduction in rare-earth pyrochlore materials, and points out an avenue to obtain low thermal conductivity in complex structural thermal insulation materials.     

Three Ln(III)-2,3,5-trichlorobenzoate coordination polymers (Ln = Tb,Ho and Er): Syntheses,structures and magnetic properties

Three novel lanthanide polymers, [Ln(III)(L)₃EtOH]_n (Ln = Tb(1), Ho(2), Er(3), HL = 2,3,5-trichlorobenzoic acid), have been solvothermal synthesized and characterized by single-crystal X-ray diffraction, infrared spectroscopy and element analyses. The three polymers crystallize in triclinic space group P-1. The Ln(III) ions are in turn bridged by double and quadruple carboxylate of L⁻ ligands to form one-dimensional (1D) chains. Magnetic studies reveal that polymer 1 demonstrates dominant ferromagnetic behavior, polymer 2 shows antiferromagnetic behavior, and polymer 3 present spin-canting behavior.     

Effects of LnAlO3 (Ln = La,Nd, Sm) additives on the properties of Ba4.2Nd9.2Ti18O54 ceramics

The effects of LnAlO₃ (Ln = La, Nd, Sm) additives on the microstructure and the dielectric properties of Ba_4.2Nd_9.2Ti₁₈O₅ (BNT) materials have been investigated. The microstructure of BNT doped with NdAlO₃ was analyzed using X-ray diffraction and scanning electron microscopy (SEM). Over 10 wt.% additions of NdAlO₃ diminished grain growth and the densifications process. In addition, typical columnar grain morphology observed in BNT ceramics was transformed to quasi-rectangular shapes accompanied by increasing porosity. XRD analysis did not reveal any second phases or modification of the BNT crystal structure. The addition of small amounts of LnAlO₃ (≤10 wt.%) increased the Q values remarkably and improved the TCf. The relative permittivity and the TCf values showed a linear decrease with increasing additions of LnAlO₃. It was observed that near zero TCf values can be achieved with addition of LnAlO₃ dopants to BNT ceramics. The Q values exhibited a non-linear behaviour with LnAlO₃ additions with maxima attained at approximately 10 wt.% LnAlO₃.     

Gas sensing and electrochemical properties of rare earthferrite,LnFeO 3 (Ln = Nd,Sm)

In this paper, nanostructured perovskite-type LnFeO₃ (Ln = Nd, Sm) oxides were synthesized by thermal treatment method (TTM). Characterization analysis conducted by X-ray diffraction (XRD), scanning electron microscopy (SEM) and micro-Raman spectroscopy, have confirmed the perovskite structure of the synthesized nanomaterials. To study the effects of Nd and Sm lanthanides substitution at the A-site on the chemical sensing performance, conductometric and electrochemical sensors based on the synthesized LnFeO₃ samples were fabricated. LnFeO₃-based conductometric and electrochemical sensors were tested for acetone and dopamine sensing, respectively. The data revealed that Nd and Sm in the A-position lead to a significant influence in the gas sensing and electrochemical properties of perovskite LnFeO₃ samples. In particular, it has been demonstrated the good gas sensing characteristics of SmFeO₃ for acetone gas (Response = R/R₀ = 8.3–20 ppm acetone at 200 °C), whereas NdFeO₃ displayed better performance as electrode for the electrochemical detection of dopamine reaching a low detection limit (LOD) of 270 nM at S/N = 3. The electrical and electrochemical characteristics of the perovskite LnFeO₃ samples were discussed in detail with respect to their chemical composition and microstructure.     

PNBE-supported metallopolymer-type hybrid materials through grafting of Ln3-benzimidazole-arrayed (Ln = Nd,Yb or Er) complex monomers with efficient NIR luminescence

Through the ring-opening metathesis polymerization (ROMP) of norbornene (NBE) with each of the obtained allyl-containing complex monomers {[Ln₃(L)₄Cl₄(MeOH)₂]·Cl} (Ln = La, 1; Nd, 2; Yb, 3; Er, 4 or Gd, 5; HL = 4-allyl-2-(1H-benzo[d]imidazol-2-yl)-6-methoxyphenol), a series of metallopolymers Poly({[Ln₃(L)₄Cl₄(MeOH)₂]·Cl}-co-NBE) were obtained, respectively. Especially for Poly(NBE-co-2) and Poly(NBE-co-3), covalently-bonded grafting endows significantly improved physical properties including efficient NIR luminescence (Φ_Nd^L = 0.58% and Φ_Yb^L = 0.88%) in solid state.     

Calcium-magnesium-alumina-silicate (CMAS) resistance characteristics of LnPO4 (Ln = Nd,Sm, Gd) thermal barrier oxides

Calcium-magnesium-alumina-silicate (CMAS) attack has been considered as a significant failure mechanism for thermal barrier coatings (TBCs). As a promising series of TBC candidates, rare-earth phosphates have attracted increasing attention. This work evaluated the resistance characteristics of LnPO₄ (Ln = Nd, Sm, Gd) compounds to CMAS attack at 1250 °C. Due to the chemical reaction between molten CMAS and LnPO₄, a dense, crack-free reaction layer, mainly composed of Ca₃Ln₇(PO₄)(SiO₄)₅O₂ apatite, CaAl₂Si₂O₈ and MgAl₂O₄, was formed on the surface of compounds, which had positive effect on suppressing CMAS infiltration. The depth of CMAS penetration in LnPO₄ (Ln = Nd, Sm, Gd) decreased in the sequence of NdPO₄, SmPO₄ and GdPO₄. GdPO₄ had the best resistance characteristics to CMAS attack among the three compounds. The related mechanism was discussed based on the formation ability of apatite phase caused by the reaction between molten CMAS and LnPO₄.     

Construction of isostructural Ln–Ag (Ln = Eu; Tb; Dy) nano-channel heterometallic coordination frameworks based on pyrazine-2-carboxylate and oxalate ligands

The self-assembly of pyrazine-2-carboxylate and oxalate with mixed-metal salts under hydrothermal conditions gave three isostructural 3D 4d-4f coordination polymers, LnAg(ox)(2-pzc)₂ · H₂O [Ln = Eu (1); Tb (2); Dy (3)] [ox = oxalate, 2-pzc = pyrazine-2-carboxylate]. All three structures exhibit same unusual 3D nanoporous heterometallic coordination frameworks constructed by zigzag lanthanide–oxalate chains and Ag(2-pzc)₂ units. Furthermore, the luminescent properties of complexes 1 and 2 are discussed.     

Facile one-pot synthesis of porous Ln2Ti2O7 (Ln = Nd,Gd, Er) with photocatalytic degradation performance for methyl orange

Porous nanocrystalline Ln₂Ti₂O₇ (Ln = Nd, Gd, Er) was prepared by a facile self-propagating combustion method using metal nitrates (Ln(NO₃)₃ (Ln = Nd, Gd, Er), TiO(NO₃)₂) and glycine. The photocatalytic activity of Ln₂Ti₂O₇ (Ln = Nd, Gd, Er) was evaluated by the photocatalytic degradation of methyl orange (MO). The results showed that the photocatalytic activity of Ln₂Ti₂O₇ (Ln = Gd, Er) with cubic pyrochlore structure was higher than that of Nd₂Ti₂O₇ with monoclinic perovskite structure and Gd₂Ti₂O₇ showed the best photocatalytic activity. The different photocatalytic activities observed for Ln₂Ti₂O₇ (Ln = Nd, Gd, Er) could be related to its different crystal structures and Ln 4f shells.     

Isostructural 3D Ln–Ag (Ln = Eu; Dy; Ho) coordination frameworks based on mixed nicotinate and oxalate ligands: Synthesis,crystal structures and luminescence

By control of mixed organic ligands with different geometries, three unusual 4d–4f heterometallic coordination polymers, [AgLn(nic)₂(ox)] · 2H₂O [Ln = Eu (1); Dy (2); Ho (3)] [nic = nicotinate; ox = oxalate] have been synthesized under hydrothermal reaction. Three structures represent 3D open heterometallic coordination frameworks that are constructed from rare zigzag lanthanide-ox-silver chains and nic linkers. Furthermore, the luminescent property of complex 1 was discussed.     

Microstructural dependence of the thermal and mechanical properties of monazite LnPO4 (Ln = La to Gd)

In this work are given some thermal and mechanical properties of monazite, related to the microstructure. This compound is a poor thermal conductive (λ < 5 W m⁻¹ K⁻¹), with a thermal expansion in between 9 and 10 × 10⁻⁶ K⁻¹ according to the considered crystallographic direction, and a relatively high specific heat (C_p ≈ 110 J mol⁻¹ K⁻¹). Mechanical properties of monazite are characteristic of a brittle behavior: bending strength is of about 100 MPa and fracture toughness is close to 1 MPa m^1/2. Porosity plays a large role on both thermal and mechanical properties pointing out the importance of controlling the whole elaboration process.     

Composition-dependent intrinsic defect structures in pyroclore RE2B2O7 (RE = La,Nd, Gd; B = Sn,Hf, Zr)

Point defects are closely correlated with various properties of pyrochlore oxides and therefore play a key role on their engineering applications. Here, the native point defect complexes in RE₂B₂O₇ (RE = La, Nd, Gd; B = Sn, Hf, Zr) under stoichiometric and nonstoichiometric compositions are studied by first-principles calculations. The O Frenkel defect complex is predicted to be the predominant defect structure in stoichiometric zirconates and hafnates, whereas the cation antisite defect complex is the predominant one in stannates. In the case of BO₂ excess, the formation of the B-RE antisite defect together with the RE vacancy and the oxygen interstitial is energetically favorable, whereas the RE-B antisite defect together with the oxygen vacancy and the RE interstitial is preferable under the RE₂O₃ excess environments. Additionally, the formation energies of the native defect complexes are greatly affected by the B-site and/or RE-site cations. The strategy on tailoring the intrinsic defect structures of these pyrochlore oxides is proposed. It is expected to guide the experiments on the defect-related property optimization through stoichiometric and nonstoichiometric compositions, so as to meet the specific engineering requirements and promote their commercial applications.     

Synchrotron x-ray spectroscopy investigation of the Ca1−xLnxZrTi2−x(Al,Fe)xO7 zirconolite ceramics (Ln = La,Nd, Gd,Ho, Yb)

When incorporating actinides into zirconolite for high-level radioactive waste immobilization, Al³⁺ and Fe³⁺ ions generally act as charge compensators. In this study, we rationally designed a series of (Ln = La, Nd, Gd, Ho, Yb) to unravel the dopant solubility and evolutions of the crystalline phase and local environment of cations through synchrotron X-ray methods. It was found that single zirconolite phase is difficult to obtain and the fraction of perovskite have an increase with x from 0.1 to 0.9 in . Formation of both zirconolite-2M and zirconolite-3O phases was observed in and . Phase transformation from zirconolite-2M to 3O occurs at x = 0.7 for while x = 0.9 for . The solubility of and to form single zirconolite-2M can reach to 0.9 f.u. and 0.7 f.u., respectively. The evolution of lattice parameters of zirconolite in is greatly related to the ionic radii of cations and substitution mechanism among the cations. X-ray absorption near edge spectroscopy revealed that Fe³⁺ ions replace both five- and six-coordinated Ti sites and the ratio of TiO₅ to TiO₆ decreases when increasing dopant concentration in the . For the local environment of Zr⁴⁺, the major form is ZrO₇ with a trace of ZrO₈.     

Low‐firing and temperature stable microwave dielectric ceramics: Ba2LnV3O11 (Ln = Nd,Sm)

Low‐firing and temperature stable microwave dielectric ceramics of Ba₂LnV₃O₁₁ (Ln = Nd, Sm) were prepared by solid‐state reaction. X‐ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate the phase purity, crystal structure, sintering behavior, and microstructure. The XRD patterns indicated that Ba₂LnV₃O₁₁ (Ln = Nd, Sm) ceramics belong to monoclinic crystal system with P2₁/c space group in the whole sintering temperature range (800°C ‐900°C). Both ceramics could be well densified at 880°C for 4 hours with relative densities higher than 96%. The Ba₂LnV₃O₁₁ (Ln = Nd, Sm) samples sintered at 880°C for 4 hours exhibited excellent microwave dielectric properties: ε_r = 12.05, Q × f = 23 010 GHz, τ_f = ?7.7 ppm/°C, and ε_r = 12.19, Q × f = 27 120 GHz, τ_f = ?16.2 ppm/°C, respectively. Besides, Ba₂LnV₃O₁₁ (Ln = Nd, Sm) ceramics could be well co‐fired with the silver electrode at 880°C.     

Thermal Expansion of Ln6WO12 (Ln = Y,Ho, Er,Yb) and Ln2WO6 (Ln = Gd,Dy, Ho) – an In Situ Synchrotron X‐ray Diffraction Study

The thermal expansion (TE) behavior of cubic and rhombohedral Ln₆WO₁₂ (Ln = Y, Ho, Er, Yb) and monoclinic Ln₂WO₆ (Ln = Gd, Dy, Ho) was investigated by synchrotron X‐ray diffraction from room temperature to approximately 1500°C. The volumetric and lattice parameter expansions were measured for all compositions in both systems, and the respective expansion coefficients were derived and fitted over the observed temperature range with a second‐order polynomial. The relative TE evolution along the unit cell edges in each phase was described from a crystallographic perspective, with the reasons for TE dynamics explained in terms of the fundamental constituent units of the structure. Analysis of the TE ellipsoid of the monoclinic Ln₂WO₆ revealed a continuous change in both its shape and orientation, with the latter effect strongly manifested in the (010) plane. A noticeable reversal of the relative expansion rates between a, and b and c lattice parameters was attributed to the rotation of the ellipsoid cross section in this plane, bringing the larger of the two eigenvectors closer to a, while the smaller one to c. Investigating the structural dynamics of the constituent layers in Ln₂WO₆ suggested that the bridging role of the Ln polyhedron centered on the only general position in the unit cell may be the reason for the rotating TE ellipsoid.     

Novel complex ceramic oxides,Ln2TiO5 (Ln = La,Sm, Gd,Tb, Dy,Ho, Er,and Yb), for polyphase nuclear waste-forms

As part of a broader study of ceramic nuclear waste-forms, four different lanthanide titanates were fabricated; La_0.1Sm_0.1Gd_0.1Tb_0.1Dy_0.3Ho_0.1Er_0.2YbTiO₅, Sm_0.3Gd_0.3Dy_0.3Yb_1.1TiO₅, Sm_0.1Gd_0.4Dy_0.4Yb_1.1TiO₅, and Sm_0.2Gd_0.2Dy_0.2Yb_1.4TiO₅. The aim was to produce single-phase novel materials with cubic symmetry, capable of incorporating a wide variety of cations and with acceptable radiation tolerance. The chemistry flexibility and radiation tolerance are some of the major desirable properties for nuclear waste-form materials. By using multiple lanthanides the average lanthanide radius can be controlled and consequently the structure, along with properties such as radiation tolerance. The radiation tolerance was assessed using in situ 1 MeV krypton irradiation and transmission electron microscopy characterization. Those materials for which cubic symmetry was achieved displayed better radiation tolerance; a greater critical fluence of ions (F_c) was required for the crystalline to amorphous transition, and a lower temperature was required to maintain crystallinity (T_c) during irradiation.     

Crystal chemistry and ion-irradiation resistance of Ln2ZrO5 compounds with Ln = Sm,Eu, Gd,and Tb

The previously unattained fabrication of single phase Ln₂ZrO₅ (Ln = Sm, Eu, Gd, and Tb) compounds via relatively low sintering temperature (1400°C) is achieved in this study using a coprecipitation method. The crystal structures have been investigated by neutron, synchrotron X-ray powder diffraction, and electron diffraction techniques. While the general long-range structure may be well described by the defect-fluorite type structure with Fmm symmetry, electron diffraction has highlighted a complex underlying modulated structure that varies between each compound. These compounds have been tested for ion-irradiation response using in situ 1 MeV krypton ions and transmission electron microscopy characterization. None of the compounds undergo a crystalline to amorphous transition, even holding at 50 K. Both the underlying fluorite and modulated superstructures are little affected by the irradiation. However, some atomic rearrangements are observed in the postirradiated electron diffraction patterns for the Sm₂ZrO₅ specimen.