Crystal structures, stability, electronic and elastic properties of 4d and 5d transition metal monoborides: First-principles calculations

Crystal structures and constitution of the binary system iridium-boron

“…The optimized lattice parameters and atomic sites at ambient pressure are compiled in Table 7. For the 1:1 stoichiometric IrB, three types of structures (hP2, hP4 and oP8) have been reported from DFT calculations [18,19,21] to be thermodynamically stable. Interestingly, our present calculation reveals a new ground state phase, oC8 (space group Cmcm), which possesses two inequivalent Ir and B Wyckoff atomic sites at 4c (0, 0.2415, 0.25) and 4c (0, 0.6027, 0.25), respectively, and it is energetically lower than the hP2 and hP4 phases by about 0.022 and 0.020 eV/atom, respectively, as shown in Fig.…”

“…At a pressure of about 5 GPa orthorhombic IrB was said to undergo a phase transition to the anti-NiAs phase. In another theoretical study [21] on the 4d and 5d transition metal monoborides, IrB with WC crystal structure has been found to be thermodynamically stable at zero pressure. From the calculation, stoichiometric IrB is mechanicall y unstable, indicating together with the difference in experimental and calculated lattice parameters, the presence of boron vacancies in the crystal structure.…”

Crystal Structure and Physical Properties of HfB4 via First-Principles Calculations

“…The calculated bulk modulus, shear modulus, Young's modulus, and Poisson's ratio of the Cmcm phase together with the reference materials mentioned above are tabulated in Table 2. As shown in Table 2, the calculated bulk modulus of the Cmcm-HfB4 (243 GPa) is larger than those of HfB [39,40], ZrB12 [63][64][65], and YB4 [8,66] but is comparable to those of HfB2 [43][44][45], HfB12 [48], and other TMB4 (TM= Fe [12,13,67,68], Cr [13,14,69], Mn [11,70], Zr [23], and Ta [27]), indicating its strong ability to resist the volume deformation. Moreover, the bulk modulus (B=243 GPa) for the Cmcm-HfB4 is in consistent with that directly obtained from the fitting results (B0=244 GPa) of the third-order Birch-Murnaghan equation of states, which further demonstrates the good accuracy of our elastic calculations.…”

“…Recently, an experimental study showed that the high-pressure cubic HfB12 phase can be successfully stabilized in the Y1-xHfxB12 system under ambient pressure [37]. Furthermore, the crystal structure and related physical properties of HfB, HfB2, and HfB12 have been widely investigated [38][39][40][41][42][43][44][45][46][47][48]. However, there is no experimental report on the synthesis of hafnium tetraborides; besides, the theoretical research works of hafnium tetraborides are also seldom up to now.…”

Электронные и механические свойства, фазовая стабильность и энергии образования точечных дефектов боронитрида Nb-=SUB=-2-=/SUB=-BN

“…Так, на-пример, модули сжатия боронитрида (B = 282.6 GPa) и борокарбида (B = 333.2 GPa) сравнимы по ве-личине с B = 283−302 GPa для различных моди-фикаций NbN [24], B = 299 GPa для Nb 2 N 3 [25], B = 262 и 308 GPa для NbB и MoB со структурой CrB [17], B = 328−341 GPa для монокарбидов молиб-дена MoC [26], B = 264−285 GPa для MoB со струк-турами NiAs, WC, NaCl и СsCl [27] и превышают значения B = 205−238 GPa для NbB со структурами NiAs и NaCl [27]. В свою очередь модули сдвига Nb 2 BN (G = 182.2 GPa) и Mo 2 BC (G = 196.8 GPa) близки к G = 198 и 202 GPa для NbB, MoB со структурой СrB [17] и G = 152−224 GPa для полиморфных модифи-каций MoC [26], но заметно выше значений G = 141 GPa для Nb 2 N 3 [25], G = 80−167 GPa для MoB со структу-рами NiAs, WC, NaCl и СsCl [27] и G = 83−135 GPa для NbB со структурами NiAs и NaCl [27].…”