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Semiconducting La2AuP3, the metallic conductor Ce2AuP3, and other rare-earth gold phosphides Ln2AuP3 with two closely related crystal structures

The compounds Ln2AuP3 were synthesized by reaction of the elemental components in evacuated silica tubes. Their crystal structures were determined from single-crystal diffractometer data. The compounds with Ln = La, Ce, and Pr crystallize with an orthorhombic U2NiC3 type structure (Pnma, Z = 4). The structure refinement for Ce2AuP3 resulted in a = 774.14(6) pm, b = 421.11(4) pm, c = 1612.3(1) pm, R = 0.019 for 1410 structure factors and 38 variable parameters. For Pr2AuP3 a residual of R = 0.024 was obtained. Nd2AuP3 crystallizes with a monoclinic distortion of this structure: P21/c, Z = 4, a = 416.14(4) pm, b = 768.87(6) pm, c = 1647.1(2) pm, β = 104.06(1)°, R = 0.022 for 1361 F values and 56 variables. The near-neighbor coordinations of the two structures are nearly the same. In both structures the gold and phosphorus atoms form two-dimensionally infinite nets, where the gold atoms are tetrahedrally coordinated by phosphorus atoms with Au-P distances varying between 245.8 and 284.2 pm. Two thirds of the phosphorus atoms form pairs with single-bond distances varying between 217.7 and 218.9 pm. Thus, using oxidation numbers the structures can be rationalized with the formulas (Ln+3)2[AuP3]-6 and (Ln+3)2Au+1(P2)-4P -3. Accordingly, La2AuP3 is a diamagnetic semiconductor. Pr2AuP3 is semi-conducting with an antiferromagnetic ground state, showing metamagnetism with a critical field of Bc = 0.5(±0.1) T. In contrast, the cerium compound is a metallic conductor, even though its cell volume indicates that the cerium atoms are essentially trivalent, as is also suggested by the ferro- or ferrimagnetic behavior of the compound. WILEY-VCH Verlag GmbH, 2001.

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]

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

RE4[P1-x(C2)x]3 (RE = La-Nd): The mixed anionic substructure formed by phosphorus and carbon

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.

Magnetic and magnetocaloric properties of Nd monopnictides

The behavior of Nd monopnictides in the paramagnetic regime is studied with a Hamiltonian that includes crystalline field interactions, molecular and quadrupolar fields. Experimental results have been obtained from polycrystalline samples, and from analysis of low field curves we deduced molecular and quadrupolar field parameters. From the magnetization data, the NdP and NdAs magnetocaloric potentials -ΔSmag are well reproduced, and their experimental isofields are in agreement with the one calculated from the model and the proposed parameters.

Phase transitions of lanthanide monophosphides with NaCl-type structure at high pressures

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.

Investigation of the photoelectronic properties of rare earth monophosphides

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