Changing the gap type of solid state boric acid by heating: a dispersion-corrected density functional study of α-, β-, and γ-metaboric acid polymorphs

Abstract

The gap type of solid state metaboric acid can be changed by temperature changes near 100 °C according to DFT calculations.

Vibrational Modes and Phonon and Thermodynamic Properties of the Metaboric Acid Polymorphs α-, β-, and γ-(BOH)3O3 within a Density Functional Theory Framework

“…Here, we follow closely the path of our previous work about dispersion-corrected DFT calculations on the structural, electronic, and optical properties of the α-, β-, and γ-(BOH) 3 O 3 polymorphs . An X-ray diffraction study of the orthorhombic α-(BOH) 3 O 3 metaboric acid polymorph was published by Peters and Milberg .…”

“…Here, we follow closely the path of our previous work about dispersion-corrected DFT calculations on the structural, electronic, and optical properties of the α-, β-, and γ-(BOH) 3 O 3 polymorphs. 15 An X-ray diffraction study of the orthorhombic α-(BOH) 3 O 3 metaboric acid polymorph was published by Peters and Milberg. 16 The structure is formed by layers of planar B 3 O 6 motifs made from three BO 3 triangles, each one sharing two oxygen atoms, so as to form a hexagonal B 3 O 3 ring; see Figure 1a,b.…”

“…Recently, the structural, electronic, and optical properties of the metaboric acid α-, β-, and γ-polymorphs were investigated through density functional theory (DFT) calculations performed at the generalized gradient approximation level improved using the Tkatchenko–Scheffler scheme to take into account dispersive interactions . With this approach, unit cell deviations Δ a , Δ b , and Δ c (in comparison with X-ray data ,, ) as small as −0.08, −0.09, and −0.06 Å for α-(BOH) 3 O 3 ; 0.00, 0.06, and −0.09 Å for β-(BOH) 3 O 3 ; and 0.01, 0.01, and 0.01 Å for γ-(BOH) 3 O 3 were obtained.…”

“…the metaboric acid α-, β-, and γ-polymorphs were investigated through density functional theory (DFT) calculations performed at the generalized gradient approximation level improved using the Tkatchenko−Scheffler scheme to take into account dispersive interactions. 15 With this approach, unit cell deviations Δa, Δb, and Δc (in comparison with X-ray data 11,16,17 ) as small as −0.08, −0.09, and −0.06 Å for α-(BOH) 3 O 3 ; 0.00, 0.06, and −0.09 Å for β-(BOH) 3 O 3 ; and 0.01, 0.01, and 0.01 Å for γ-(BOH) 3 O 3 were obtained. The layered α-MA polymorph was predicted to have a direct gap of 6.26 eV, which is close to the values found recently for the boric acid triclinic (H 3 BO 3 -2A, 6.25 eV) and trigonal (H 3 BO 3 -3T, 6.28 eV) indirect gap systems.…”

Phosphorescence by Trapping Defects in Boric Acid Induced by Thermal Processing

“…This effect is shared by the orthorhombic (𝛼-I) and monocline (𝛽-II) structures, while the cubic (𝛾-III) structure has no actual participation of boron atoms in the LUCB (Lowest Unoccupied Conduction Band). [31] This evidence shows that the electronic properties of boric acid, the various polymorphs of metaboric acid, and even boron oxide in its glassy and crystalline form cannot explain the presence of radiative recombinations in the visible spectrum of any sort, fluorescence, or phosphorescence.…”