Low-temperature thermal properties of yttrium and lutetium dodecaborides

Abstract

The heat capacity (C p ) and dilatation (α) of YB 12 and LuB 12 are studied. C p of the zone-melted YB 12 tricrystal is measured in the range 2.5-70 K, of the zone-melted LuB 12 single crystal in the range 0.6-70 K, and of the LuB 12 powder sample in the range 4.3-300 K; α of the zone-melted YB 12 tricrystal and LuB 12 single crystals is measured in the range 5-200 K. At low temperatures a negative thermal expansion (NTE) is revealed for both compounds: for YB 12 at 50-70 K, for LuB 12 at 10-20 K and 60-130 K. Their high-temperature NTE is a consequence of nearly non-interacting freely oscillating metal ions (Einstein oscillators) in cavities of a simple cubic rigid Debye lattice formed by B 12 cage units. The Einstein temperatures are ∼254 and ∼164 K, and the Debye temperatures are ∼1040 K and ∼1190 K for YB 12 and LuB 12 respectively. The LuB 12 low-temperature NTE is connected with an induced low-energy defect mode. The YB 12 superconducting transition has not been detected up to 2.5 K.

Effect of electron-phonon coupling on the superconducting transition temperature in dodecaboride superconductors: A comparison ofLuB12withZrB12Teyssier1, Lortz2, Petrović3 et al. 2008Phys. Rev. B474410View full textAdd to dashboardCite

“…4͒. 7,27 The low-temperature T 3 regime of the lattice specific heat does not extend beyond a few Kelvin, as shown by the large positive curvature of the normal-state curve in Fig. 3.…”

“…5,27 Figure 3 presents the specific heat C / T of LuB 12 , in comparison to that of ZrB 12 reported in Ref. 7, in the temperature range from 350 mK to 10 K on a logarithmic temperature scale.…”

“…This value is slightly smaller than values reported in literature. 5,27 As electron-electron interactions are weak in this family of borides, the Sommerfeld constant is mainly related to electron-phonon interactions. The Sommerfeld constant corresponds therefore to a dressed density of states at the Fermi level ͑1+ ep ͒N͑E F ͒ = 0.11 states eV −1 atom −1 , which is slightly lower than the value of ZrB 12 .…”

Raman study of coupled electronic and phononic excitations in LuB12

“…The details are presented in 17 . Measurements were carried out on samples with natural isotopic composition and samples enriched with isotopes B 10 and B 11 .…”

Аномальные низкочастотные фононы в ZrB-=SUB=-12-=/SUB=-

“…Детали получения образцов ZrB 12 и LuB 12 представлены в [21]. Измерения были проведены как на образцах с естественным изотопным составом, так и на образцах, обогащенных изотопами 10 B и 11 B. Аппаратура и детали эксперимента описаны в [19].…”