Chevrel phases have an open lattice in which cations can be inserted. These cations are generally located in cavity 1 or 2. We present here the crystallographic structure of selenide compounds in which 3d ions are inserted. These cations have an original position in cavity 2. These phases should have low lattice thermal conductivity and are currently being investigated for thermoelectric application. Good thermoelectric materials are also semiconducting. We present here band-structure calculations on these 3d ion Chevrel phase selenides: TiMo 6 Se 8 is the only one found to be semiconducting. CrMo 6 Se 8 , FeMo 6 Se 8 , and NiMo 6 Se 8 are metallic and might be magnetic.
Chevrel phases have an open lattice with large voids in which cations can be inserted. These cations are good scattering centers for phonons. The thermal conductivity of these compounds must be low. Chevrel phases are generally metallic, but we calculated the density of states of several compounds and we found that Zn2Mo6Se8, Cd2Mo6Se8, TiMo6Se8 are semiconducting whereas SnMo6Se8, Cu2Mo6Se8 and CrMo6Se8 are metallic. We are currently trying to synthesize Zn2Mo6Se8 by different ways.
Chevrel phases, , present large voids in their lattice, where cations can be inserted. These cations are weakly bound and constitute good scattering centres for phonons. The lattice thermal conductivity of these compounds must be very low, and these phases are then good candidates for thermoelectric application. But most of them are metallic and superconducting. Some band structure calculations have been performed in order to find a semiconducting one. and are found to be metallic and semiconducting.
The increase in the microwave surface resistance Rs of high Tc superconductors at elevated microwave power levels is reported for both oriented and unoriented Tl-based films as a function of rf magnetic field at 820 MHz and 18 GHz. The application of dc magnetic fields produces qualitatively similar increases in Rs and in the surface reactance Xs. The increase in Rs with dc field is shown to arise from simple decoupling of grains by intergranular magnetic flux. The increase in Rs with microwave power, on the other hand, is a consequence of hysteretic intergranular processes.
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