High-pressure crystal structure of the non-linear optical compound BiB₃O₆ from two-dimensional powder diffraction data

Our recently proposed method for automatic detection, calibration and evaluation of Debye–Scherrer ellipses using pattern-recognition techniques and advanced signal filtering was applied to the two-dimensional powder diffraction data of the non-ferroelectric, non-centrosymmetric non-linear optical (NLO) compound α-BiB₃O₆ as a function of pressure. At ambient conditions, α-BiB₃O₆ crystallizes in the space group C2 (phase I). In the pressure range between P = 6.09 and 6.86 GPa, it exhibits a first-order phase transition into a structure with the space group C1 (P1) [phase II at P = 8.34 GPa: a = 7.4781 (6), b = 3.9340 (4), c = 6.2321 (6) Å, α = 93.73 (1), β = 102.93 (1), γ = 90.76 (1)°, and V = 178.24 (3) ų]. Non-linear compression behaviour over the entire pressure range is observed, which can be described by two Vinet relations in the ranges from P = 0.0 to 6.09 GPa, and from P = 6.86 to 11.6 GPa. The extrapolated bulk moduli of the high-pressure phases were determined to be K₀ = 38 (1) GPa for phase I, and K₀ = 114 (10) GPa for phase II. The crystal structures of both phases were refined against X-ray powder diffraction data measured at several pressures between 0.0 and 11.6 GPa. The structural phase transition of α-BiB₃O₆ is mainly characterized by a reorientation of the [BO₃]³⁻ triangles, the [BO₄]⁵⁻ tetrahedra and the lone electron pair which is localized at Bi³⁺, in order to optimize crystal packing.

Computing details

Figures

(BiB3O6-alpha) bismuth borate - alpha at P = 4.3 GPa

Crystal data

B3BiO6	V = 199.31 (3) Å^3
Mr = 337.41	Z = 2
Monoclinic, C2	Dx = 5.622 Mg m^−3
a = 7.3786 (5) Å	Synchrotron radiation, λ = 0.44397 Å
b = 4.3992 (3) Å	µ = 12.57 mm^−1
c = 6.3388 (5) Å	T = 293 K
β = 104.374 (5)°	× × mm

Data collection

137 independent reflections	k = ?→?
h = ?→?	l = ?→?

Refinement

Refinement on F^2
37 parameters

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Biso*/Beq
Bi1	0	0	0
B1	0.5	0.128 (9)	0.5
B2	0.2641 (11)	0.014 (7)	0.7105 (12)
O1	0.3555 (4)	0.9178 (19)	0.5542 (10)
O2	0.3985 (13)	0.3134 (15)	0.3049 (6)
O3	0.2961 (10)	0.1631 (15)	0.9058 (12)

(BiB3O6-epsilon) bismuth borate - epsilon at P = 8.34 GPa

Crystal data

B3BiO6	γ = 90.756 (7)°
Mr = 337.41	V = 178.24 (3) Å^3
Triclinic, C1	Z = 2
a = 7.4781 (6) Å	Dx = 6.287 Mg m^−3
b = 3.9340 (4) Å	Synchrotron radiation, λ = 0.44397 Å
c = 6.2321 (6) Å	µ = 14.05 mm^−1
α = 93.728 (8)°	T = 293 K
β = 102.933 (6)°	× × mm

Data collection

206 independent reflections	k = ?→?
h = ?→?	l = ?→?

Refinement

Refinement on F^2
69 parameters

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Biso*/Beq
Bi	0.9955 (12)	0.0418 (19)	0.9874 (19)
B1	0.4628 (18)	0.121 (3)	0.4501 (19)
B2	0.2601 (16)	−0.041 (3)	0.6695 (11)
B3	0.7338 (16)	0.009 (4)	0.242 (2)
O1	0.2818 (10)	−0.0495 (17)	0.4533 (17)
O2	0.5886 (10)	−0.078 (2)	0.3439 (12)
O3	0.4030 (13)	0.4406 (15)	0.3532 (15)
O4	0.5975 (15)	0.242 (3)	0.6704 (9)
O5	0.3384 (12)	0.089 (3)	0.870 (2)
O6	0.665 (2)	0.133 (2)	0.0441 (11)