I. Shirotani

Pressure-induced phase transitions of lanthanide monoarsenides LaAs and LuAs with a NaCl-type structure

Abstract By use of synchrotron radiation the powder X-ray diffraction of lanthanide monoarsenides LaAs and LuAs with a NaCl-type structure has been studied up to 60 GPa at room temperature. First-order phase transitions with the crystallographic change were found at around 20 GPa for LaAs, and 57 GPa for LuAs. The high-pressure form of LaAs is a tetragonal structure and can be viewed as a distorted CsCl-type structure. The atoms in the tetragonal structure are located at La: 0, 0, 0; As: 1/2, 1/2, 1/2. The space group is P4/mmm. The structural change to the tetragonal structure occurs with the volume collapse of about 10%. The structure of these high-pressure phases of LuAs is unknown. The volume vs. pressure curves for LaAs and LuAs are fitted by a Birch equation of state. The bulk moduli of both arsenides are 92±6 GPa for LaAs and 85±3 GPa for LuAs. The high-pressure structural behavior of LaX (X=P, As and Sb) and LnAs (Ln=lanthanide) with the NaCl-type structure is discussed.

XANES STUDY OF RARE-EARTH VALENCY IN LRU4P12 (L=CE AND PR)

Valency of Ce and Pr in LRu4P12 (L = Ce and Pr) was studied by L2,3-edge x-ray absorption near-edge structure (XANES) spectroscopy. The Ce-L3 XANES spectrum suggests that Ce is mainly trivalent, but the 4f state strongly hybridizes with ligand orbitals. The band gap of CeRu4P12 seems to be formed by strong hybridization of 4f electrons. Pr-L2 XANES spectra indicate that Pr exists in trivalent state over a wide range in temperature, 20 < T < 300 K. We find that the metal-insulator (MI) transition at TMI = 60 K in PrRu4P12 does not originate from Pr valence fluctuation.

Metal-Insulator Transition in PrRu 4 P 12 with Skutterudite Structure

The low temperature properties of PrRu{sub 4}P {sub 12} and PrOs{sub 4}P {sub 12} have been studied by means of electrical resistivity and magnetic susceptibility measurements. The resistivity of PrRu{sub 4}P {sub 12} decreases with decreasing temperature from room temperature to about 60K, but increases sharply with decreasing temperature below 60K. A metal-insulator transition is found at around 60K. The susceptibility of the phosphide shows no distinct anomaly at this temperature. No significant change in the powder x-ray diffraction pattern of PrRu{sub 4}P {sub 12} is detected down to 10K. The anomalous behavior may arise from a 4f instability of the Pr ion. {copyright} {ital 1997} {ital The American Physical Society}

Micro-probed raman scattering study of ternary ruthenium phosphides with filled skutterudite-type structure

Abstract LnRu4P12 (Ln = La, Ce, Pr, Nd, Sm, Gd and Tb) with a filled skutterudite-type structure has been studied by using a micro-probed Raman scattering technique. Raman spectra have been observed and analyzed in terms of the phosphide-based filled skutterudite-type structure. The mode at around 380 cm−1 is assigned to the motion of P atoms. Another mode at around 440 cm−1 is related to the vibrations involving Ln atoms. Apart from CeRu4P12, the shifts of each mode are well scaled by cell volume or rare earth mass. This fact suggests that LnRu4P12, not including CeRu4P12, are isostructural and have the same electric properties at room temperature.

Magnetic properties of Sm-based filled skutterudite phosphides

Abstract Filled skutterudites SmFe4P12 and SmOs4P12 have been prepared at high temperature and high pressure. The temperature dependence of electrical resistivity in both compounds shows metallic behavior. The magnetic susceptibility and specific heat measurements indicate that SmFe4P12 shows a ferromagnetic ordering at 1.5 K , whereas SmOs4P12 is an antiferromagnet with a TN of 4.6 K .

Superconductivity of binary and ternary molybdenum phosphides prepared at high pressure

Abstract Binary and ternary molybdenum phosphides have been prepared at temperatures between 1200 and 1700°C under 4 GPa. An electrical resistivity and a dc magnetic susceptibility of the molybdenum phosphides were measured at low temperatures. The superconducting transition temperatures (Tcs) of binary molybdenum phosphides are 7 K for Mo3P, 5.8 K for Mo8P5 and 3 K for Mo4P3. Phosphorus-rich compounds MoP, MoP2 and MoP4 do not show the superconductivity down to 2 K. Ternary molybdenum phosphides MoNiP and MoRuP show the superconducting transition at around 15.5 K. The superconductivity in MoNiP and MoRuP is due to the Mo 4d electrons. The Mo–Mo bonds in the molybdenum phosphides are very important for the enhancement of the superconductivity.

Low-energy spin fluctuations in filled skutterudites YbFe4Sb12 and LaFe4Sb12 investigated through 121Sb nuclear quadrupole and 139La nuclear magnetic resonance measurements

We have elucidated low-energy spin fluctuations in the new filled skutterudites YbFe4Sb12 and LaFe4Sb12 synthesized at high pressures, through 121Sb nuclear quadrupole resonance (NQR) and 139La nuclear magnetic resonance (NMR) measurements. The longitudinal spin?lattice relaxation rate 1/T1 of 121Sb in YbFe4Sb12 provides evidence that upon cooling below ~20?K, the compound transforms from the localized 4f electron state of Yb3+ ions to a nonmagnetic heavy Fermi liquid state, originating from the mixing of 4f electrons with conduction electrons. Whereas, the Curie?Weiss type behaviour of the 139La Knight shift and 121Sb- 1/T1 in LaFe4Sb12 indicate that the compound remains in the localized electron state down to 1.4?K, it in fact originates from 3d electrons of Fe in [Fe4Sb12 ] anions. In both compounds, the transversal nuclear spin?spin relaxation rate 1/T2 exhibits a clear peak at and ?K, respectively. The origin of the 1/T2 peak is discussed in terms of the freezing of the thermal vibration of Sb cages or rare-earth ions filled in each Sb cage. By comparing the experimental results of the present study with those previously reported for the compounds synthesized at ambient pressure, it is pointed out that both the strongly correlated electron properties and the thermal vibrations are greatly modified with the increase of rare-earth atom deficiency.

Metal-insulator transition in Pr Ru 4 P 12 and Sm Ru 4 P 12 investigated by optical spectroscopy

Electronic structures of the filled-skutterudite compounds

Superconductivity of new filled skutterudite YFe4P12 prepared at high pressure

\mathrm{Pr}{\mathrm{Ru}}_{4}{\mathrm{P}}_{12}

Specific heat around metal-insulator transition of filled skutterudite PrRu4P12

and