Study of LiBC [Top][Japanese]


(Start 2/17, 2003)(Update 3/14, 2019)
[Outline] We found the lattice anomaly of LiBC[1][2], HBC[4], C6B2[7] under a, b-axis compression and HBC[6], h-MgB(h-BN type structure)[5][6] under c-axis compression. Lattice constants c for LiBC, HBC, C6B2 contract under a, b-axis compression. Lattice constants a(b) for h-MgB, HBC contract under c-axis compression. These anomalous behavior show a kind of negative Poisson ratios.
A crystal structure of LiBC is hexagonal (symmetry: P63/mmc) and B-C and Li layered structure (A-B stacking). HBC, h-MgB and C6B2 are hypothetical compounds. HBC is the same crystal structure of LiBC. h-MgB is the hexagonal-BN crystal structure (P63/mmc). LiBC (A-B stacking) is semiconductor. HBC and h-MgB are metallic. The lattice contraction of LiBC, HBC under Pxy = 50 GPa and h-MgB under Pz = 50 GPa is about 0.01 A. This is too small to observe experimentally. Furthermore, the lattice contraction of a-axis for HBC under Pz = 20 GPa is quite small (0.001 A). This anomaly of HBC disappears under Pz = 50 GPa. The lattice contraction of C6B2 under Pxy = 50 GPa is about 0.1 A, which is about 1 % of lattice constant c. A interlayer interaction of C6B2 is very weak (related with van der Waals force) and it may be problematic in the DFT-LDA calculation. Further, it is noted that C6B2 has a possibility of superconductivity[7].

[Method] Calculational methods are first-principles molecular dynamics (FPMD) using the pseudopotential (NCPS2K[go to other site]) + plane waves and Wien2K [package].

[Related Materials] HBC[4][6], NaBC, MgBC, MgC2, h-MgB[5][6], C6B2[7] etc.

In detail, Please see "references" below.
[Band] structure of LiBC (A-B stacking, P63/mmc symmetry, png [12 kb])
[Band] structure of LiBC (A-A stacking, Semi-metallic, P6m2 symmetry, png [27.5 kb])
[Band] structure of HBC (A-B stacking, P63/mmc symmetry, png [9.3 kb])
[Band] structure of h-MgB (Hexagonal-BN structure:P63/mmc symmetry, png [12.2 kb])

(References)
[1] K. Kobayashi and M. Arai, "LiBC and related compounds under high pressure", Physica C 388 - 389 (2003) 201 - 202 (LT23).
[2] K. Kobayashi and M. Arai, "Lattice Anomaly of LiBC and Related Compounds under Anisotropic Compression", Journal of the Physical Society of Japan, Vol. 72, No. 2 (2003) 217.
[3] K. Kobayashi, M. Arai and K. Yamamoto, "Electronic and lattice properties of MgB2 and related phases under various compression conditions", Journal of the Physical Society of Japan, Vol. 72, No. 11 (2003) 2886:(Related paper).
[4] K. Kobayashi, M. Arai and T. Sasaki, "Lattice Anomalies of MBC (M = H, Li, Na) Under Anisotropic Compression", Trans. MRS-J, Vol. 29, No. 8, 3799-3802 (2004)[IUMRS-ICAM2003]:(Related paper).
[5] K. Kobayashi and M. Arai, "Lattice anomaly of MgB(h-BN) under anisotropic compression", Mater. Trans., Vol. 45, No. 5, (2004) 1465 - 1468.
[6] K. Kobayashi and M. Arai, "Lattice anomaly of MgB(h-BN) and related compounds under various compression conditions", Molecular Simulation, Vol. 30, No. 13 - 15 (2004) 981 - 986 (in Proceedings ICMS-CSW2004).

[C6B2](ISS2004)
[7] K. Kobayashi, Y. Zenitani and J. Akimitsu, "First-Principles Study of C6B2", Physica C, Vol. 426-431, Part 1. (2005) 374 - 380 [ISS2004]. <-- As a result of more accurate calculations, we find that anharmonicity of C6B2 is weak (b4/(a2)2 is about 1).
[8] K. Kobayashi, M. Arai and K. Yamamoto, "First-Principles Study of C6M2 (M = B, Al, Mg, Li), C7B and Related Compounds", Mater. Trans., Vol. 47, No. 11 (2006) 2629 - 2637[AlC2, MgC2, LiC2, LiB2].
[9] K. Kobayashi, M. Arai and K. Yamamoto, "First-principles study of C6B2 and related compounds", in proceedings of IWSDRM2005 (STAM, Vol. 7, Supplement 1 (2006) 71 - 77).

Related [papers] of LiBC (go to other site), of [MgB2]
(Future schedule)
(Previous works)
(Related references)

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