- Thermoelectric properties of LaFePO1-xFx and LaFeAs1-xFx possibility of the hidden mass enhancement of LaFeAsO1-xFx
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We investigated thermoelectric properties for polycrystalline oxypnictide LaFePO1-xFx and LaFeAs1-xFx. The temperature (T) and F-doping dependences of resistivity (ρ) and Seebeck coefficient (S) are quite different between these compounds. In contrast to a monotonic T dependence and an absence of large F-doping dependences of ρ and S for LaFePO1-xFx, the S for LaFeAs1-xF x for 0 a large power factor of about 37 μW/K2 cm at 53K and a dimensinless thermoelectric figure of merit (ZT) of about 0.08 at 110K for LaFeAsO0.89F0.11. The non-monotonic behavior of S with the relatively large absolute value and the reported T dependence of Hall coefficient for LaFeAs1-xFx seem to evidence an instability of an orbital order accompanying a stripe-typeAF order even in the over F-doping region for LaFeAs1-xFx and indicate a possibility of a hidden mass enhancement of LaFeAs1-xFx.
- Okuda, Tetsuji,Hirata, Wataru,Takemori, Akira,Suzuki, Shinnosuke,Saijo, Satoshi,Miyasaka, Shigeki,Tajima, Setsuko
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- Iron-based layered superconductor: LaOFeP
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We report superconductivity in an iron-based layered oxy-pnictide LaOFeP. LaOFeP is composed of an alternate stack of lanthanum oxide (La3+O2--) and iron pnictide (Fe2+P3-) layers. Magnetic and electrical resist
- Kamihara, Yoichi,Hiramatsu, Hidenori,Hirano, Masahiro,Kawamura, Ryuto,Yanagi, Hiroshi,Kamiya, Toshio,Hosono, Hideo
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- Non-monotonic change of electronic properties by As substitution in LaFeP(O,F)
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The discovery of superconductivity at 28 K in fluorine doped LaFeAsO stimulated a great interest in iron arsenide superconductors. But many differences of physical properties exist between FeP and FeAs 1111 oxypnictide superconductors. To reveal its origin, we synthesized LaFeP1-xAs xO0.9F0.1, and investigated the x-dependence of the physical properties. In contrast to a monotonic change of lattice parameters, Tc and T-dependence of resistivity show non-monotonic change.
- Saijo,Suzuki,Miyasaka,Tajima
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- Nickel-based oxyphosphide superconductor with a layered crystal structure, LaNiOP
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A layered oxyphosphide, LaNiOP, was synthesized by solid-state reactions. This crystal was confirmed to have a layered structure composed of an alternating stack of (La3+O2-)+ and (Ni 2+P3-)-. We found that the resulting LaNiOP shows a superconducting transition at ~3 K. This material exhibited metallic conduction and Pauli paramagnetism in the temperature range of 4-300 K. The resistivity sharply dropped to zero and the magnetic susceptibility became negative at a superconducting transition occurs. The volume fraction of the superconducting phase estimated from the diamagnetic susceptibility reached ~40 vol % at 1.8 K, substantiating that LaNiOP is a bulk superconductor.
- Watanabe, Takumi,Yanagi, Hiroshi,Kamiya, Toshio,Kamihara, Yoichi,Hiramatsu, Hidenori,Hirano, Masahiro,Hosono, Hideo
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- Third time's the charm: Intricate non-centrosymmetric polymorphism in Ln SiP3(Ln = la and Ce) induced by distortions of phosphorus square layers
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Complex polymorphic relationships in the LnSiP3 (Ln = La and Ce) family of compounds are reported. An innovative synthetic method was developed to overcome differences in the reactivities of the rare-earth metal and refractory silicon with phosphorus. Reactions of atomically mixed Ln + Si with P allowed for selective control over the reaction outcomes resulting in targeted isolation of three new polymorphs of LaSiP3 and two polymorphs of CeSiP3. In situ X-ray diffraction studies revealed that the developed method bypasses formation of the thermodynamic dead-end, the binary SiP. Careful re-determination of the crystal structure ruled out the previously reported ordered centrosymmetric structure of CeSiP3 and showed that the main LnSiP3 polymorphs crystallize in the non-centrosymmetric Pna21 and Aea2 space groups featuring distinct distortions of the regular P square net to yield either cis-trans 1D phosphorus chains (Pna21) or disordered-2D phosphorus layers (Aea2). The disordered 2D nature of the P layers in the Aea2 LaSiP3 polymorph was confirmed by Raman spectroscopy. A unique centrosymmetric P21/c polymorph was observed for LaSiP3 and has a completely different crystal structure lacking P layers. Consecutive polymorphic transformations at increasing temperatures for LaSiP3(Pna21 → P21/c → Aea2) were derived from optimized synthetic profiles and confirmed by a combination of phonon computations and experimental in situ and ex situ annealings. Crystal structures of the LaSiP3 polymorphs were verified via advanced solid state NMR analysis using 31P MAS and 31P{139La} double resonance techniques. A combination of phonon and electronic structure calculations, NMR T1 relaxation times, UV/Vis/NIR spectroscopy, and resistivity measurements revealed that all the reported polymorphs are semiconductors with resistivities and thermal conductivities strongly dependent on the degree of distortion of P square layers in the crystal structure. Reported here, non-centrosymmetric LnSiP3 polymorphs with tunable resistivity and thermal conductivity provide a platform for the development of novel functional materials with a wide range of applications.
- Adeyemi, Adedoyin N.,Akopov, Georgiy,Ho, Kai-Ming,Kovnir, Kirill,Lee, Shannon J.,Mark, Justin,McBride, Brennan C.,Miller, Gordon J.,Paterson, Alexander L.,Perras, Frédéric A.,Sen, Sabyasachi,Viswanathan, Gayatri,Wang, Cai-Zhuang,Won, Juyeon,Yuan, Bing,Zhang, Feng
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- Searching for key parameter for determining Tc in Fe-based superconductors: Study of P/As substitution in RFe(P,As)(O,F) [R=La and Nd]
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We have investigated the relation between the temperature-dependence of resistivity and superconducting transition temperature Tc in RFeP1-xAsxO0.90F0.10 (x=01.0) (R=La and Nd). In contrast to the lin
- Miyasaka, Shigeki,Takemori, Akira,Saijo, Satoshi,Suzuki, Shin-Nosuke,Tajima, Setsuko
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- Antiperovskite Superconductor LaPd3P with Noncentrosymmetric Cubic Structure
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Antiperovskites are a promising candidate structure for the exploration of new materials. We discovered an antiperovskite phosphide, LaPd3P, following our recent synthesis of APd3P (A = Ca, Sr, Ba). While APd3P and (Ca,Sr)Pd3P were found to be tetragonal or orthorhombic systems, LaPd3P is a new prototype cubic system (a = 9.0317(1) ?) with a noncentrosymmetric space group (I4ˉ 3m). LaPd3P exhibited superconductivity with a transition temperature (Tc) of 0.28 K. The upper critical field, Debye temperature, and Sommerfeld constant (γ) were determined to be 0.305(8) kOe, 267(1) K, and 6.06(4) mJ mol-1 K-2 f.u.-1, respectively. We performed first-principles electronic band structure calculations for LaPd3P and compared the theoretical and experimental results. The calculated Sommerfeld constant (2.24 mJ mol-1 K-2 f.u.-1) was much smaller than the experimental value of γbecause the Fermi energy (EF) was located slightly below the density of states (DOS) pseudogap. This difference was explained by the increase in the DOS at EF due to the approximately 5 atom % La deficiency (hole doping) in the sample. The observed Tc value was much lower than that estimated using the Bardeen-Cooper-Schrieffer equation. To explain the discrepancy, we examined the possibility of an unconventional superconductivity in LaPd3P arising from the lack of space inversion symmetry.
- Eisaki, Hiroshi,Fujihisa, Hiroshi,Gotoh, Yoshito,Hase, Izumi,Hirose, Hishiro T.,Ishida, Shigeyuki,Iyo, Akira,Kawashima, Kenji,Ninomiya, Hiroki,Terashima, Taichi,Yoshida, Yoshiyuki
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p. 18017 - 18023
(2021/12/01)
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- High-pressure synthesis, structure and properties of new ternary pnictides La3TiX5 (X = P, As)
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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.
- Cao, Lipeng,Deng, Zheng,Duan, Lei,Jin, Changqing,Li, Wenmin,Li, Zhi,Wang, Xiancheng,Yu, Runze,Zhang, Jun,Zhao, Jianfa
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- RE4[P1-x(C2)x]3 (RE = La-Nd): The mixed anionic substructure formed by phosphorus and carbon
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The rare-earth phosphide carbides RE4[P1-x(C 2)x]3 (RE = La, Ce, Pr, Nd) represent the first example of a mixed anionic substructure formed by phosphorus and carbon, being the first step toward the formation of the mixed inorganic P-C species. The peculiarities of the crystal structure, magnetic properties, XAS data, and quantum chemical calculation results confirm the ionic nature of the interaction beween the rare-earth cations RE and phosphorus anions, while complex interaction of π states of the C2 anions and d (and/or f) states of the RE components is indicated. Thus, despite the extensive chemical analogy between the phosphide carbides and phosphide suicides, the atomic interactions stabilizing the structural motif are slightly different.
- Chizhov, Pavel S.,Schnelle, Walter,Burkhardt, Ulrich,Schmidt, Marcus,Prots, Yurii,Antipov, Evgeny V.,Grin, Yuri
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p. 1318 - 1325
(2011/01/06)
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- Some phosphide halides of lanthanum and related compounds
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The pnictide halides La2I2P, La2I 2As, La2I2Sb, La2Br2P and Y2Br2P have been synthesized from lanthanum and yttrium, red phosphorus, arsenic, and
- Oeckler, Oliver,Mattausch, Hansjürgen,Simon, Arndt
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p. 1377 - 1382
(2008/10/09)
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- Phase Diagram of the La-Co-P System at 670 K
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Interaction of the components in the La-Co-P system was studied by X-ray analytical methods. The isothermal section of the phase diagram at 670 K was plotted. It was confirmed that two previously known ternary phosphides, LaCo2P2 and LaCo5P3, occur in the system.
- Kuz'ma,Chikhrii,Davydov
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p. 768 - 770
(2008/10/08)
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- Phase transitions of lanthanide monophosphides with NaCl-type structure at high pressures
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Lanthanide monophosphides LnP (Ln = La, Ce, Pr, Nd, Sm, Gd, Tb, Tm and Yb) with a NaCl-type structure have systematically been prepared at high temperatures. Using synchrotron radiation, X-ray diffractions of LnP have been studied up to 61 GPa at room temperature. The NaCl-CsCl transition for CeP is found at around 25 GPa. First-order phase transitions of LnP (Ln = La, Pr and Nd) with the crystallographic change occur at around 24, 26 and 30 GPa, respectively. The structure of the high pressure phases of these phosphides is a body center tetragonal structure (Ln: 0, 0, 0; P: 1/2, 1/2, 1/2; space group P4/mmm), which can be seen as the distorted CsCl-type structure. The Pr-P distance in the high pressure form of PrP is 2.789 A. This almost agrees with the sum of covalent radii of Pr and P. The Pr-P bond has the covalent character at very high pressures. Similar results are also obtained for LaP and NdP. The pressure-induced phase transitions of SmP, GdP, TbP, TmP and YbP occur at around 35, 40, 38, 53 and 51 GPa, respectively. The structure of the high pressure phase is unknown. The phase transitions of LnP with many f-electrons are not due to the mechanism of the ordinary NaCl-CsCl transition. The transition pressures of LnP increase with decreasing the lattice constants in the NaCl-type structure, which decrease with increasing atomic number of the lanthanide atoms.
- Adachi, Takafumi,Shirotani, Ichimin,Hayashi, Junichi,Shimomura, Osamu
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p. 389 - 393
(2008/10/09)
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- Phase Equilibria in the {La, Ce}-Fe-P Systems
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Isothermal sections of the La-Fe-P and Ce-Fe-P phase diagrams at 1070 K (up to 30 mol% of a rare-earth metal) and at 870 K (30-100 mol %) are constructed by using X-ray diffraction techniques. The compounds LaFe2P2, CeFe2P2, and Ce2Fe12P7 are synthesized by direct reaction of the constituent elements at the temperature of investigation.
- Chikhrii,Shevchuk
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p. 1258 - 1260
(2008/10/08)
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- Investigation of the photoelectronic properties of rare earth monophosphides
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The optical, electrical and photoelectronic properties of rare earth monophosphides (LnP, Ln=La, Nd, Sm and Y) have been studied. The experimental results indicate that their resistivities are low, the electric conduction in all of them is N-type, the ene
- Jian, Meng,Yufang, Ren
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p. 485 - 488
(2008/10/08)
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