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Relevant academic research and scientific papers

High-pressure synthesis, structure and properties of new ternary pnictides La3TiX5 (X = P, As)

The new ternary pnictides La3TiX5 (X = P, As) and the solid solutions of La3Ti(Sb1-xAsx)5 (x = 0–1) and La3Ti(As1-yPy)5 (y = 0–1) were synthesized under high pressure and high temperature conditions. The crystal structure of La3TiX5 (X = P, As) was determined from the X-ray powder diffraction data. These compounds crystallize in a hexagonal Hf5Sn3Cu-anti type structure with the space group P63/mcm and lattice parameters a = 8.7927 ? and c = 5.7643 ? for La3TiP5, and a = 9.0267 ? and c = 5.9071 ? for La3TiAs5, in which the face-sharing TiX6 octahedral chains running along the c axis are separated by La3+ in the interstice sites with a distance about 9 ?, presenting a strong one-dimensional crystal structure. Physical properties measurements indicate La3TiX5 (X = P, As) are Pauli paramagnetic metals. The calculations reveal that La3+ ions are not perfectly ionic owing to the non-negligible contributions of La to the density of state (DOS) at the Fermi level and bridge the X atoms between the chains, which make the samples to be 3-dimensional metals. What's more, the change of X in La3TiX5 from Sb to P increases the ionicity of La3+ and thus decreases the electron hopping between the conducting chains.

La6Pd2+xSb15 (x = 0.28): A rare-earth palladium intermetallic compound with extended pnictogen ribbons

A new intermetallic ternary compound La6Pd2.28Sb15 was synthesized from the reaction of lanthanum and palladium metals in a molten antimony flux. The compound crystallizes in the orthorhombic space group Immm with a ?= ?4.3082(9) ?, b ?= ?15.399(3) ? and c ?= ?19.689(4) ?. The crystal structure contains a three-dimensional framework of Sb squares and ribbons that extend along the a axis, including complex Sb–Sb bonding. La6Pd2.28Sb15 is diamagnetic, with a magnetic susceptibility weakly dependent on temperature (T). The resistivity (ρ) decreases when lowering the temperature, indicating metallic behavior, and at low temperatures ρ depends quadratically on T. Interestingly, both the Hall resistivity and magnetoresistance present a nonlinear dependence on the applied magnetic field, suggesting a multiband behavior. This is supported by density-functional electronic structure calculations which show a complex Fermi surface originated in the antimonide substructures and containing both electron and hole pockets as well as open sheets.

Synthesis and Transport Properties of the Family of Zintl Phases Ca3RESb3(RE = La-Nd, Sm, Gd-Tm, Lu): Exploring the Roles of Crystallographic Disorder and Core 4f Electrons for Enhancing Thermoelectric Performance

Zintl phases with complex crystal structures have been studied as promising candidate materials for thermoelectric (TE) applications. Here, we report the syntheses of the family of rare-earth metal Zintl phases with the general formula Ca4-xRExSb3 (x ≈ 1; RE = La-Nd, Sm, Gd-Tm, Lu). The structural elucidation is based on refinements of single-crystal X-ray diffraction data for 12 unique chemical compositions. The cubic structure is confirmed as belonging to the anti-Th3P4 structure type (space group I4ˉ 3d, no. 220, Z = 4), where the Ca and RE atoms share the same atomic site with ca. 75 and 25% occupancies, respectively. Such crystallographic disordering of divalent Ca and trivalent RE atoms in the structure provides a pathway to intricate bonding. The latter, together with the presence of heavy elements such as Sb and the lanthanides, are expected to enhance the scattering probability of phonons, thereby leading to low thermal conductivity κ comparable to that of the ordered RE4Sb3. The drive of the hypothetical parent compound Ca4Sb3 to be stabilized by alloying with rare-earth metals can be understood following the Zintl-Klemm concept, as the resultant formula may be rationalized as (Ca2+)3RE3+(Sb3-)3, indicating the realization of closed-shell electronic configurations for all elements. This notion is confirmed by electronic structure calculations, which reveal narrow bandgaps Eg = 0.77 and 0.53 eV for Ca3LaSb3 and Ca3LuSb3, respectively. In addition, the incorporation of RE atoms into the structure drives the phase into a state of a degenerate semiconductor with dominant hole charge carriers.

New ternary La2Sb-type compounds, ScRESb (RE = La, Ce, Pr, Nd, Sm, Tb), and the oxygen stuffed variant Sc4Yb4Sb 4O

Scandium rare-earth metal antimonides, ScRESb (RE = La, Ce, Pr, Nd, Sm, Tb) were synthesized from scandium metal and binary RESb at 1770 K in tantalum ampoules. According to X-ray analyses of the crystal structures, they adopt the tetragonal ScCeSi-type of structure (space group I4/mmm, Pearson code tI12), a variant of La2Sb, with a fully ordered atom distribution. Especially in ScSmSb and ScTbSb, the scandium atoms are distorted from an ideal 4 4 net in a way to form Sc nets of squares and rhombi in order to adjust to the lattice shrinkage in the ab plane, caused by the lanthanide contraction. Finally the structure changes from La2Sb to Sc 2Sb-type (anti-PbFCl-type), when terbium is replaced by dysprosium. The respective compound with ytterbium was only found when stoichiometric amounts of oxygen were present, resulting in Sc4Yb4Sb 4O, a La2Sb-type variant stuffed with oxygen. A structure field map, based on specific geometric parameters, easily allows for distinguishing between oxygen stuffed and oxygen-free compounds. Magnetic susceptibility measurements of ScCeSb, ScPrSb, and ScNdSb indicate Curie-Weiss behavior with ferromagnetic exchange coupling underlying. The magnetic moments correspond to the expected values for RE3+. Copyright

Synthesis, crystal structure, and electronic properties of the tetragonal (REIREII)3SbO3 Phases (RE I = La, Ce; REII = Dy, Ho)

In our efforts to tune the charge transport properties of the recently discovered RE3SbO3 phases (RE is a rare earth), we have prepared mixed (REIREII)3SbO3 phases (REI = La, Ce; REII = Dy, Ho) via high-temperature reactions at 1550 C or greater. In contrast to monoclinic RE3SbO 3, the new phases adopt the P42/mnm symmetry but have a structural framework similar to that of RE3SbO3. The formation of the tetragonal (REIREII)3SbO 3 phases is driven by the ordering of the large and small RE atoms on different atomic sites. The La1.5Dy1.5SbO3, La1.5Ho1.5SbO3, and Ce1.5Ho 1.5SbO3 samples were subjected to elemental microprobe analysis to verify their compositions and to electrical resistivity measurements to evaluate their thermoelectric potential. The electrical resistivity data indicate the presence of a band gap, which is supported by electronic structure calculations.

Resolving composition and structure of RE-Sb-O-C natural superlattice phases (RE = La, Ho)

A family of rare earth antimonide oxycarbides have been prepared and structurally characterized. These superlattice phases are constructed from NaCl-type RESb slabs sandwiched between RE-O-C layers. Depending on the carbon content and synthetic conditions, three different RE-Sb-O-C structures can be obtained. At lower temperatures,RE9-δSb 5(O,C)5 phases are obtained for RE = La, Ho. These phases adopt a stuffed Sc2Sb-type structure with P4/nmm symmetry. An O/C mixture, in which the O/C ratio is larger than 4:1, is randomly distributed within the RE-O-C layers. The RE atoms are highly disordered within the oxide layer. At temperatures above the melting point of the samples, RE 9Sb5O4C phases with P4/n symmetry are produced. The RE-O-C layers in RE9Sb5O4 are fully ordered; the RE sites are well defined, and the O and C atoms occupy the tetrahedral and square-pyramidal voids, respectively. At high temperatures, a new ordered La14Sb8O7C structure with P4bm symmetry was discovered. The La14Sb8O7C phase is structurally similar to RE9Sb5O4C and features orderedarrangements of La and O/C atoms in the La-O-C layer. The RE9-δSb5(O,C)5, RE 9Sb5O4C and La14Sb8O 7C phases appear to be charge-balanced, and their compositions and structures are controlled by the O/C ratio. Parallel preparative experiments revealed the importance of carbon in the formation of these layered phases. In addition, it has been established that the purity of the rare earth metals influences the compositions and structures of the products.

Synthesis, crystal and electronic structures of new narrow-band-gap semiconducting antimonide oxides RE3SbO3 and RE 8Sb3-δO8, with RE = La, Sm, Gd, and Ho

In the search for high-temperature thermoelectric materials, two families of novel, narrow-band-gap semiconducting antimonide oxides with the compositions RE3SbO3 and RE8Sb3-δO 8 (RE = La, Sm, Gd, Ho) have been discovered. Their synthesis was motivated by attempts to open a band gap in the semimetallic RESb binaries through a chemical fusion of RESb and corresponding insulating RE 2O3. Temperatures of 1350 °C or higher are required to obtain these phases. Both RE3SbO3 and RE 8Sb3-δO8 adopt new monoclinic structures with the C2/m space group and feature similar REO frameworks composed of RE4O tetrahedral units. In both structures, the Sb atoms occupy the empty channels within the REO sublattice. High-purity bulk Sm and Ho samples were prepared and subjected to electrical resistivity measurements. Both the RE3SbO3 and RE8Sb 3-δO8 (RE = Sm, Ho) phases exhibit a semiconductor-type electrical behavior. While a small band gap in RE 3SbO3 results from the separation of the valence and conduction bands, a band gap in RE8Sb3-δO 8 appears to result from the Anderson localization of electrons. The relationship among the composition, crystal structures, and electrical resistivity is analyzed using electronic structure calculations.

Structural and 121Sb M?ssbauer spectroscopic investigations of the antimonide oxides REMnSbO (RE = La, Ce, Pr, Nd, Sm, Gd, Tb) and REZnSbO (RE = La, Ce, Pr)

Quaternary antimonide oxides REMnSbO (RE = La, Ce, Pr, Nd, Sm, Gd, Tb) and REZnSbO (RE = La, Ce, Pr) were synthesized from the RESb monoantimonides and MnO, respectively ZnO, in sealed tubes at 1170 K. Single crystals were obtained from NaCl/KCl salt fluxes. The ZrCuSiAs-type (space group P4/nmm) structures of LaMnSbO (a = 423.95(7), c = 955.5(27) pm, wR2 = 0.067, 247 F2), CeMnSbO (a = 420.8(1), c = 950.7(1) pm, wR2 = 0.097, 250 F2), SmMnSbO (a = 413.1(1), c = 942.3(1) pm, wR2 = 0.068, 330 F2), LaZnSbO (a = 422.67(6), c = 953.8(2) pm, wR2 = 0.052, 259 F2), and NdZnSbO (a = 415.9(1), c = 945.4(4) pm, wR2 = 0.109, 206 F2) were refined from single crystal X-ray diffractometer data. The structures consist of covalently bonded (RE3+O2-)+ and (T2+Sb 3-)- layers with weak ionic interlayer interactions. The oxygen and transition metal atoms both have tetrahedral coordination within the layers. 121Sb Mossbauer spectra of the REMnSbO and REZnSbO compounds show single antimony sites with isomer shifts close to -8 mms-1, in agreement with the antimonide character of these compounds. PrMnSbO and NdMnSbO show transferred hyperfine fields of 8 T at 4.2 K.

Pressure-induced phase transitions in lanthanide monoantimonides with a NaCl-type structure

By use of synchrotron radiation the powder x-ray diffraction of LnSb (Ln=lanthanide) with a NaCl-type structure has systematically been studied up to 40 GPa at room temperature. First-order phase transitions with the crystallographic change occur for LnSb at high pressures. The structure of the high-pressure phases of LnSb is classified into three groups. The lighter LnSb (Ln=La, Ce, Pr, and Nd) have the tetragonal structure (distorted CsCl-type) at high pressures. The high-pressure form of the middle LnSb (Ln=Sm, Gd, and Tb) is unknown. The heavier LnSb (Ln=Dy, Ho, Er, Tm, and Lu) show the typical NaCl-CsCl (B1-B2) transition at high pressures though the same transition is not observed in the heavier LnP and LnAs. The transition pressures of LnSb increase with decreasing lattice constant in the NaCl-type structure and do not depend on the structure of their high-pressure phases. The high-pressure structural behavior of LnSb is discussed.

Magnetic properties of alkaline earth and lanthanoid iron antimonides AFe4Sb12 (A = Ca, Sr, Ba, La-Nd, Sm, Eu) with the LaFe4P12 structure

The magnetic properties of the nine title compounds were studied by magnetic susceptibility measurements with a SQUID magnetometer between 2 and 300K. At temperatures above 100 K, all compounds with the exception of the cerium and samarium compounds show Curie-Weiss behaviour. The effective magnetic moments of the alkaline earth compounds vary between 3.7 ± 0.2 μB and 4.0 ± 0.2 μB per formula unit. For LaFe4Sb12 the moment is smaller (3.0 ± 0.2 μB) indicating a higher degree of electronic saturation within the Fe4Sb12 polyanion. At lower temperatures, the magnetic susceptibilities of these compounds deviate from the Curie-Weiss law, however, they remain field independent. A mixed valent behaviour is observed for the cerium compound and the samarium compound reflects the Van Vleck paramagnetism of the Sm3+ ions. The magnetic susceptibilities of the other lanthanoid compounds correspond to the sums of the susceptibilities of the Fe4Sb12 polyanion and the Ln3+ and Eu2+ ions, respectively. These antimonides order ferromagnetically with Curie temperatures varying between 5(1) K for PrFe4Sb12 and 82(2) K for EuFe4Sb12. The magnetic properties of these compounds are discussed within the framework of a rigid band structure.