Thermal expansion of the one-dimensional conductor K2Pt(CN)4Br0.3·xH2O and K2Pt(CN)4·xH2O

Measurements of the thermal expansion coefficients of K₂Pt(CN)₄Br_0.3· xH₂O and K₂Pt(CN)₄·xH₂O show a large anisotropy of the a-and c- directions. Their temperature dependence could be described by a simple Grüneisen theory. In the range from 80–330°K no anomaly indicating a Kohn-Peierls transition could be found.     

Lattice anharmonicities in K2Pt(CN)4Br0.3 · 3H2O

A difference of about 7 per cent between the velocities of first and zero sound has been observed in K₂Pt(CN)₄Br_0.3 · 3H₂O for longitudinal waves travelling along the direction of the Pt chains. Large temperature and pressure derivatives of the elastic module c₃₃ have been found.     

Electrical conduction studies on one-dimensional Cs2[Pt(CN)4](FHF)0.39 and Rb2[Pt(CN)4](FHF)0.40

Variable temperature (300-40 K) 4-probe d.c. conduction studies on Cs₂[Pt(CN)₄](FHF)_0.39 and Rb₂[Pt(CN)₄](FHF)_0.40 are described. In these salts T_3D occurs at a lower temperature than in K₂[Pt(CN)₄]Br_0.3·3H₂O and this is attributed to the absence of an inter-chain network of hydrogen bonded water molecules in the bifluorides.     

Spin relaxation in the quasi-one-dimensional conductor Rb2Pt(CN)4(FHF)0.4

We analyze the electron paramagnetic resonance linewidth in Rb₂Pt(CN)₄(FHF)_0.4 as a function of temperature. Above 60 K, the results are interpreted as a superposition of spin-phonon and spin-spin relaxation effects. The dominant contribution to the relaxation rate l/T₂ has a dipolar origin in contrast to the spin-phonon origin observed in K₂Pt(CN)₄Br_0.3 · H₂O. This difference could arise from different anisotropy ratios of the transfer integrals. The influence of the interchain coupling is also discussed.     

The water content of the quasi one-dimensional conductor K2Pt(CN)4Br0.3·xH2O as a function of external water-vapor pressure

It is shown that all 3 of the water molecules of crystallization can be extracted and added again in the quasi one-dimensional conducting compound K₂Pt(CN)₄Br_0.3·xH₂O by varying the external water vapor pressure. In passing from the trihydrate to the anhydrous state the lattice parameters change by 1.2% in c-direction and by 4.5% in a-direction. The vapor pressure measurements yield a series of stable states of hydration, specially at laboratory atmosphere.     

Coupling of the CDW and the water mode in K2Pt(CN)4Br0.3⋯3.2H2O

In previous work we have observed the amplitude mode of the charge density wave (CDW) in K₂Pt(CN)₄Br_0.3?3.2H₂O (KCP) by means of Raman scattering. New measurements made on deuterated material, K₂Pt(CN)₄Br_0.3?3.2D₂O (KCP1), show the same mode but shifted from 44 to 38 cm_?1, maintaining the symmetry properties and temperature dependence of frequency and linewidth. This considerable isotope effect is interpreted in terms of a coupling of the CDW with the water stretching mode, which by the deuteration is shifted from 3494 cm^?1 in KCP to 2560 cm^?1 in KCP1 according to the change in atomic mass. Both of these modes exhibit A₁(z) symmetry. At 5 K the resulting decoupled frequency of the CDW amplitude mode is 57 cm^?1, and the coupling energy about 140 cm^?1. A discussion of the temperature dependence of various important quantities is given. The present results show that the water molecules, which are located in between the Pt chains are strongly involved in the eigenvector of the CDW amplitude mode.     

Observation of electromagnetic resonances in crystals of K2Pt (CN)4 Br0.3.3H2O at microwave frequencies

Electromagnetic dielectric resonances in the range 8–11 GHz have been observed in millimeter sized crystals of K₂Pt(CN)₄Br_0.3.3H₂O. This observation results directly from the existence of large dielectric constants; values for the longitudinal and transverse dielectric constants at 4°K are estimated to be ?6 >～ 3000 and ?⊥ ?4.     

Proton NMR in the one-dimensional conductor K2Pt(CN) 4Br0.33H2O

The orientation of the proton-proton vectors of the water molecules in the quasi-one-dimensional conductor K₂Pt (CN) ₄Br_0.33H₂O have been determined. Temperature dependent rotations of the water molecules have been observed.     

Phenomenological treatment of electronic response in one-dimensional metals

The dielectric function for electrons in one-dimensional systems is calculated using a somewhat extended model of interrupted strands by incorporation of hopping processes. Applied to K₂Pt(CN) ₄Br_0.3·3H₂O the simple phenomenological model explains qualitatively the experimental results in the whole frequency range.     

The giant Kohn phonon anomaly in a Peierls semiconductor

It is shown that the ‘giant Kohn phonon anomaly’ which is characteristic of a one-dimensional metal may also be found in a Peierls semiconductor. A simple model reflecting roughly the LA-phonon dispersion of K₂Pt(CN)₄Br_0.3 · 3H₂O has been used to get numerical results.     

Evidence for the fröhlich collective mode in the one-dimensional conductor K2[Pt(CN)4] Br0.3 · 3H2O from far infrared reflection

Far infrared and infrared reflection measurements on single crystals of the one dimensional conductor K₂[Pt(CN)₄] Br_0.3 · 3H₂O have been performed at 4.2K, 62K and 300K for light polarized parallel (E6z) and perpendicular (E ? z) to the platinum chains. At 4.2K and 62K a strong structure is observed in the E6z spectrum near 40 cm^-1 which is not observable at 300K. This structure is interpreted as due to the Fröhlich collective 2q_F-phonon mode.     

Soliton energy band for the six-fold degenerated CDW in the K2Pt(CN)4Br0.3·3.2H2O system

The formation of soliton bands in the quasi-one-dimensional mixed valence planer platinum compound K₂Pt(CN)₄Br_0.3·3.2H₂O (KCP) as a result of overlapping soliton wave functions is considered. A solitonic energy band dependence on temperature and the associated phonon modes of the soliton array are suggested to be responsible for the ESR linewidth broadening observed in this material for temperatures above 85 K.     

Optical conductivity and electron interaction in the one-dimensional metal K2Pt (CN)4 Br0.3 · 3H2O

Experimental and theoretical investigations of the optical conductivity of K₂Pt (CN)₄Br_0,3 · 3H₂O single crystals for phonon energies near the plasma edge are reported. The imaginary part of the dielectric function is determined by only two scattering processes: Elastic scattering of holes by the Coulomb potentials of randomly distributed Br-ions and inelastic scattering by excitation of plasmons.     

Anisotropic thermopower in the quasi-one-dimensional conductor K2Pt(CN)4Br0.3·3H2O

The temperature-dependence of the Seebeck-coefficient has been measured along and perpendicular to the direction of high conductivity on single crystals of K₂Pt(CN)₄Br_0.3·3H₂O. This material has previously been shown to behave like a one-dimensional metallic conductor at optical frequencies. The thermopower is small but distinctly anisotropic and of negative sign.     

Influence of hydrostatic pressure on the plasma reflection edge of K2Pt(CN)4Br0.3 · 3H2O

A blue shift of the optical plasma reflection edge of the one-dimensional metal K₂Pt(CN)₄Br_0.3 · 3H₂O under hydrostatic pressures up to 7.2 katm has been observed. The shift (75 cm^?1katm^?1±30%) is interpreted as an increase of the plasma frequency and is correlated with the changes in the interatomic distances under pressure.     

Studies on partially oxidised one-dimensional bis(oxalato)platinate salts containing divalent cations

The preparation and electrical conduction properties of the isostructural one-dimensional conductors Ni_0.84[Pt(C₂O₄)₂]·6H₂O(Ni-OP) and Mn_0.81[Pt(C₂O₄)₂]·6H₂O(Mn-OP) are described. Ni-OP exhibits a similar tem dependence of conductivity to the isostructural compounds Co_0.83[Pt(C₂O₄)₂]·6H₂O(Co-OP) and Zn_0.81[Pt(C₂O₄)₂]·6H₂O whereas the behaviour of Mn-OP is rather like that of K₂[Pt(CN)₄]Br_0.3·3H₂O. These differences are discussed in terms of the variation from compound to compound of the critical temperature for the formation of the “non-Peierls” superstructure (T_c) and the temperature at which the CDW/PD on adjacent conducting chains undergo three-dimensional ordering (T_3D). The variation of thermopower with temperature for Co-OP and Mg_0.82[Pt(C₂O₄)₂]·6H₂O is reported and related to the conduction properties and phase changes which have been observed for these compounds. For the isostructural series M_0.8[Pt(C₂O₄)₂]·6H₂O (M = Mg, Mn, Co, Ni or Zn) the variation of (T_3D) from compound to compound is related to differences in the polarizing power of the cations.     

Incommensurate pinning mechanism in KCP

An incommensurate pinning mechanism based on the Q-quasimodulated bromine (Br^-) distribution (Q being twice the Fermi wavevector reduced to the first Brillouin zone) is proposed in K₂Pt(CN)₄Br_0.3 3.2H₂O (KCP) which quantitatively accounts for the neutron scattering and far infrared optical spectroscopy data in this material.     

Fluctuations and three-dimensional ordering in weakly coupled linear conductors

Fluctuations in a system of weakly coupled linear chains are investigated within the functional generalization of the Landau theory. The onset of three-dimensional ordering as a function of the interchain coupling and the order-parameter correlation function aboveT _c are discussed. The results are compared with neutron scattering experiments on the quasi-linear conductor K₂Pt(CN)₄Br_0.3 · 3 D₂O.     

Analternative model for the conductivity behavior of K2Pt(CN)4Br0.3·3H2O

It is shown that the reordering of the bromine atoms into a new cubic lattice at low temperatures can produce the changes observed in the conductivity behavior of the mixed valence salt K₂Pt(CN)₄Br_0.32·3H₂O. The optical data are examined in terms of an RPA calculation of the dielectric response of the crystal and it is noted that a periodic potential can reproduce the observed structure in the imaginary part without the need for identifying the charge carriers.