ACTA

Defect Mode in LaB₆

M. Anisimov^a, A. Bogach^a, V. Glushkov^a,b, S. Demishev^a,b, N. Samarin^a, S. Gavrilkin^c, K. Mitsen^c, N. Shitsevalova^d, A. Levchenko^d, V. Filippov^d, S. Gabani^e, K. Flachbart^e, N. Sluchanko^a
^aA.M. Prokhorov General Physics Institute of RAS, Vavilov str. 38, 119991 Moscow, Russia
^bMoscow Institute of Physics and Technology, Institutskii per. 9, 141700 Dolgoprudnyi, Russia
^cP.N. Lebedev Physical Institute of RAS, Leninskii Prospect 53, 119991 Moscow, Russia
^dI. Frantsevich Institute for Problems of Materials Science NAS, Krzhyzhanovsky str. 3, 03680 Kiev, Ukraine
^eInstitute of Experimental Physics SAS, Watsonova 47, 040 01 Košice, Slovakia

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The specific heat of high quality La^NB₆ (N=10, 11, natural) single crystals is investigated in a wide range of temperatures 2 - 300 K. The obtained data allow to estimate correctly (i) the electronic γ· T term of specific heat (γ ≈ 2.4 mJ/(mol·K²)), (ii) the contribution from quasilocal vibrating mode of La³⁺ ions (Θ_E ≈ 150 - 152 K), (iii) the Debye-type term from rigid boron cages (Θ_D ≈ 1160± 40 K). Our data also suggest an additional defect-mode component (iv) which may be attributed to a contribution of 1.5% boron vacancies in LaB₆. The obtained results may be interpreted in terms of formation of two level systems, which appear when La³⁺ ions are displaced from their centrosymmetric positions in the cavities of rigid boron cages, apart from randomly distributed boron vacancies in the LaB₆ matrix.

DOI: 10.12693/APhysPolA.126.350
PACS numbers: 65.40.Ba