X-ray scattering and electrical resistivity measurements were performed on SmNiC2. Satellite peaks characterized by an incommensurate wave vector (0.5, eta, 0) appear below 148 K, at which the resistivity shows an anomaly. The temperature dependence of thermal diffuse scattering above 148 K suggests critical phonon softening. These results indicate the formation of a charge-density-wave. The satellite peaks abruptly disappear and the resistivity sharply decreases when a ferromagnetic transition takes place at 17.7 K.

Vanadium dioxide shows metal-insulator transition (MIT) at around 341 K with several orders of change in resistivity through structural transition from low temperature monoclinic phase to high temperature tetragonal phase. Thus, characteristics of MIT in vanadium dioxide strongly depend on crystalline structure. In this study, we investigated crystalline lattice parameters of vanadium dioxide films by X-ray diffraction analyses. The films were deposited on c-sapphire substrates by using ICP-assisted sputtering method. The vanadium dioxide film grows epitaxially on sapphire (001) surface with its a-c plane parallel to the substrate. Films fabricated by pulsed laser deposition (PLD) method were also served for lattice parameter analyses. We selected four diffractions in order to derive lattice parameters of monoclinic crystal, a, b, c and incline angle r. In sputter-deposited films prepared at 673 K, expansion of a with relative difference of around 0.5 % and shortening of c with relative difference of around -0.3 % compared to those in bulk crystal were observed. Angle r was smaller than bulk one keeping the c times sinr close to bulk crystal. As for b axis perpendicular to the substrate, the length was coincident with bulk value within -0.1 %. On the other hand, in films prepared by PLD method at 773 K, lattice parameters were close to those of bulk crystal revealing high quality crystalline growth in PLD under adequate substrate temperature. We performed XRD measurements for in-situ heated vanadium dioxide films and found expansion of c axis and shortening of a axis than tetragonal bulk values. Matching of cell volume between two phases was exaimined. Minute correlation between crystalline structure and MIT characteristics will be presented in the convention. Ternary compounds RNiC2 (R = rare-earth elements) have various magnetic transitions and exhibit anomalous temperature dependences of the electrical resistivity. In SmNiC2, a first-order ferromagnetic transition takes place at TC = 17.5 K. The electrical resistivity of this compound decreases with decreasing temperature down to 150 K below room temperature. It shows a sudden increase around 150 K. One of the possible origins of the anomalous temperature dependence is the formation of a charge-density-wave (CDW) state. In order to detect the transition to the CDW state as well as the critical phenomena associated with it, we have performed x-ray diffraction and diffuse scattering measurements on SmNiC2 using synchrotron radiation at the BL46XU of the SPring-8. We found that satellite peaks characterized by a wavevector (0.5, η, 0) appear at 148 K, corresponding to the sharp inflection in the temperature dependence of the resistivity. Diffuse scattering peaks exist at the satellite positions even at room temperature. Their intensities increase with decreasing temperature toward 148 K. These results show that the CDW transition takes place and that the corresponding phonon softening occurs above the transition temperature. The satellite intensity increases wit...