Thermal expansion study of Fe1−xCoxSi

The thermal expansion of (Fe1−yNiy)Si

“…V T3 0 0 (Å 3 ) 90.328(4) 90.286(6) 90.171(7) α 0 (K −1 ) 3.88(4) × 10 −5 3.56(5) × 10 −5 3.56(5) × 10 −5 α 1 (K −2 ) 1.51(5) × 10 −8 1. data and model is good but for the FeSi the thermal expansions predicted by the fit are too high at ~100 K and too low at ~300 K. Our experimental data are in excellent agreement with previous dilatometry measurements (Mandrus et al 1994). As expected from the volume data, the thermal expansion of FeSi is greater than that of the Ni doped phases at low temperatures and the thermal expansions converge at high temperatures.…”

“…The unit-cell volume of FeSi has been measured between 4 and 1173 K by time of flight neutron diffraction Vočadlo et al (2002) and is reported in other studies at non-ambient temper ature (Sales et al 1994, Delaire et al 2013. The thermal expansion of FeSi has been measured by dilatometry by both Krentsis et al (1972) and Mandrus et al (1994) who also measured the thermal expansion of Fe 1−y Co y Si for 0 ⩽ y ⩽ 0.05 between 40 and 300 K and showed that the addition of Co to FeSi significantly reduces the thermal expansion and the change is related to the suppression of its semi-conducting properties.…”

“…Many of the physical properties of end-member FeSi have unusual temperature dependencies, including the thermal expansion (Mandrus et al 1994), heat capacity (Mani et al 2008), Seebeck coefficient (Sales et al 1994) and magnetic susceptibility (Sales et al 1994). The unusual properties are caused by its peculiar electron band structure and FeSi is commonly described as either a narrow band-gap semiconductor (Delaire et al 2011) or a Kondo Insulator (Samuely et al 1996, Mani et al 2008.…”

“…Hybridisation between the silicon 3p and iron 3d bands creates a small gap in the electronic density of states (DOS), which in FeSi (as well as RuSi and OsSi) coincides with the Fermi level (Mattheiss and Hamann 1993, Jarlborg 1997. Estimates of the size of the band-gap (E g ) in FeSi range between ~30 and 105 meV from experiments (Schlesinger et al 1993, Mandrus et al 1994, 1995, Sales et al 1994, Park et al 1995, Samuely et al 1996, Jarlborg 1997, Fäth et al 1998, Menzel et al 2009 although one indirect estimate is as low as 10 meV (Menzel et al 2009). Electronic DOS calculation estimates the band gap to be ~120 meV (Delaire et al 2011).…”

Kondo insulator description of spin state transition in FeSb2

“…If the degeneracies of levels separated by E g are equal, we expect the peak at a temperature equivalent to ∆ = 2.4T peak . 27,28 While we cannot extract the electronic contribution from the phonons in C P (Fig. 6a shows that it is ∼10% of the measured value of C P ), since the Grüneisen parameter Γ = 3Bα/C P remains roughly constant, the Schottky term should be reflected in the thermal conductivity as well.…”