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 Å. 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.     

Systematic high-pressure synthesis of new filled skutterudites with heavy lanthanide, LnFe4P12 (Ln=heavy lanthanide, including Y)

New filled skutterudites with heavy lanthanide, LnFe₄P₁₂ (Ln=Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) have systematically been prepared for the first time by the high-pressure technique. The relationship between lattice constants and atomic numbers of lanthanide (including Y) is established for LnFe₄P₁₂. Electrical and magnetic properties of several new filled skutterudites with heavy lanthanide have been studied at low temperatures; YFe₄P₁₂ shows a superconducting transition at around 7 K, and DyFe₄P₁₂ behaves as a ferromagnet below 10 K. Electrical and magnetic anomalies in DyFe₄P₁₂ and YFe₄P₁₂ are mainly discussed.     

Use of high molecular weight amines for end-point indication in the complexometric titration of Iron(III) with thiocyanate as indicator

Summary A new type of end-point indication for the complexometric titration of iron(III) is proposed. A 10% carbon tetrachloride solution of Amberlite LA-1 is applied for the extraction of the thiocyanate complexes. Very sharp color change of the organic phase from red to pale yellow gives the accurate end point for titrations with 0.01M EDTA as in the Variamine Blue B method.

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Zusammenfassung Eine neue Methode zur Endpunktanzeige bei der komplexometrischen Titration, von Eisen(III) wird vorgeschlagen. Eine 10%ige Tetrachlorkohlen-stofflösung von Amberlite LA-1 wird zum Ausschütteln der Thiocyanatkomplexe angewendet. Ein sehr scharfer Farbumschlag der organischen Phase von rot nach blaßgelb zeigt den Endpunkt für Titrationen mit 0,01-m ÄDTA so genau wie bei der Variaminblau-B-Methode an.

     

Physicochemical properties of alkali metal cation-TCNQ anion radical salts

Simple alkali metal cation-TCNQ anion radical salts are classified in two groups from the differences in their physicochemical properties and crystal structures. Li-, Na-, K-, and Rb(I)-TCNQ are comprised in Group A. Li-TCNQ exhibits distinct behavior from other salts in Group A. Rb(II)- and Cs-TCNQ belong to Group B. Phase transitions, electrical conductivities, and absorption spectra in these simple salts are closely related to their crystal structures.     

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

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.     

A resistance minimum and the electronic structures of some one-dimensional Pt-complexes at high pressures

The effect of pressure has been measured up to 650 kbar on the electrical resistance in six one-dimensional Pt-complexes, including two mixed valence ones. SrPt(CN)₄·2H₂O, MgPt(CN)₄·7H₂O and BaPt(CN)₄·4H₂O do not show a resistance minimum, contrary to other d⁸-metal complexes, suggesting a considerable contribution of π¹ orbitals of CN^- ligands to the conduction.     

Electronic structure of black phosphorus studied by X-ray photoelectron spectroscopy

The X-ray photoelectron spectrum of black phosphorus has been measured for the first time. The features in the valence band spectrum are found to be in good agreement with those of the valence state density recently calculated on the basis of a pseudopotential method. The 2s and 2p core spectrum of black phosphorus is also discussed.     

Phase transitions in N—n-propylpyridinium-TCNQ2 and N—n-butylpyridinium-TCNQn at high pressures

The electrical resistivity of N-n-propylpyridinium-TCNQ₂ (NPPy-TCNQ₂) and N-n-butylpyridinium-TCNQ_n (NBPy-TCNQ_n) has been measured as a function of temperature and pressure. Phase transitions in these salts have been studied at high pressures. The transition temperature (T_c) in NPPy-TCNQ₂ at atmospheric pressure increased with increasing pressure at the rate of dT_c/dP = + 12.0 degkbar^?1. The value of volume change calculated from the Clapeylon-Clausius relation was + 4.4 cm³ mol^?1. The electrical resistivity along the a- and c-axis increased with increasing pressure below 7 kbar. This anomalous electrical behaviour is closely related to the crystal structure of NPPy-TCNQ₂. The resistivity dropped sharply at about 11 kbar. This abrupt change may be due to a new pressure induced phase transition.The T_c of the NBPy-TCNQ_n increased remarkably with increasing pressure up to 0.7 kbar, above which the phase transition disappeared. The phase transitions of N-n-alkyl-substituted pyridinium TCNQ salts depend strongly on the nature of cations.     

Evidence for a Peierls-Fröhlich state of one-dimensional platinum complex,K1.81Pt(C2O4)2·2H2O

Chemical analyses and electrical conductivity measurements were made on K_xPt(C₂O₄)₂·nH₂O (KDOX). X os 1.62 for α-KDOX and 1.81 for γ-KDOX. 2k_F calculated from the degree of partial oxidation shows that the lattice modulation wave in the superstructure of γ-KDOX is produced by the condensation of 2k_F phonon.