Superdense Hexagonal BP and AlP with Quartz Topology: Crystal Chemistry and DFT Study

Abstract

The superdense hexagonal phosphides BP and AlP, whose structures are formed by distorted tetrahedra and characterized by quartz-derived (qtz) topology, were predicted from crystal chemistry and first principles as potential high-pressure phases. From full geometry structure relaxations and ground state energy calculations based on quantum density functional theory (DFT), qtz BP and AlP were found to be less cohesive than the corresponding cubic zinc-blende (zb) phases with diamond-like (dia) topology, but were confirmed to be mechanically (elastic constants) and dynamically (phonons) stable. From the energy–volume equations of state, qtz phases were found to be energetically favorable at small volumes (high pressures), with zb-to-qtz transition pressures of 144 GPa for BP and 28 GPa for AlP. According to the electronic band structures and the site projected density of states, both phosphides exhibit larger band gaps of the zinc-blende phases compared to the qtz phases; the smaller values for the latter result from the smaller volumes per formula unit, leading to increased covalence.

High-Pressure Phases of Boron Pnictides BX (X = As, Sb, Bi) with Quartz Topology from First Principles

“…The corresponding pressures, 71 GPa and 51 GPa, were estimated using the most reliable B 0 values calculated in the framework of the thermodynamic model (Table 4), while B 0 ' values were fixed at 4. Thus, with increasing pnictogen atomic number, a drastic decrease in the zb-to-qtz transition pressure is observed from 144 GPa for BP [20] down to 51 GPa for BBi.…”

“…The structures of the currently known zinc-blende boron pnictides (BN, BP, and BAs) have dia topology (as cubic diamond) [18], which is characterized by the spatial arrangement of BN 4 , BP 4 , or BAs 4 perfect (angle ∠109.47 • ) sp 3 -like corner-sharing tetrahedra in three-dimensional 3D nets. Recently, we discovered significant structural densification of zinc-blende BN and BP by adopting a quartz-derived structure (qtz topology) characterized by distorted corner-sharing BN 4 and BP 4 tetrahedra [19,20].…”

“…In this context, the present work extends our investigation to boron pnictides with heavier elements (As, Sb, and Bi). As in previous works [19,20], the studies are based on quantum mechanics calculations of the ground-state energy structures and derived properties in the framework of the density functional theory (DFT) [21,22]. It is shown that BX phases (X = As, Sb, Bi) with qtz topology are cohesive and stable both mechanically (elastic constants and their combinations) and dynamically (phonon band structures).…”

Novel tetragonal boron pnictides BX (X = N, P, As, Sb, Bi) with square B2X2 motifs from crystal chemistry and first principles

“…Very recently, we have ab initio predicted superdense hexagonal boron pnictides BX (X = N, P, As, Sb, Bi) with quartz (qtz) topology [10][11][12]. In the present work, we used the (C1) 4 (C2) 4 template structure to predict and investigate within DFT a new family of tetragonal equiatomic boron pnictides BX with crb topology that exhibit only B-X bonds, avoiding energetically unfavorable B-B or X-X bonds.…”

Novel Tetragonal Boron Pnictides BX (X = N, P, As, Sb, Bi) with Square B2X2 Motifs from Crystal Chemistry and First Principles

“…Table 1) during the transformation from C 8 to (C1) 4 (C2) 4 . Very recently, we have ab initio predicted superdense hexagonal boron pnictides BX (X = N, P, As, Sb, Bi) with quartz (qtz) topology [10][11][12]. In the present work, we used the (C1) 4 (C2) 4 template structure to predict and investigate within DFT a new family of tetragonal equiatomic boron pnictides BX with crb topology that exhibit only B-X bonds, avoiding energetically unfavorable B-B or X-X bonds.…”