Ca(BF4)2·xH2O redefined from powder diffraction as hy­dro­gen-bonded Ca(H2O)4(BF4)2 ribbons

Le Bail, A.

doi:10.1107/S2053229625004395

Download citation

Format		BIBTeX
		EndNote
		RefMan
		Refer
		Medline
		CIF
		SGML
		Plain Text
		Text

Download citation

Format		BIBTeX
		EndNote
		RefMan
		Refer
		Medline
		CIF
		SGML
		Plain Text
		Text

research papers

STRUCTURAL
CHEMISTRY

ISSN: 2053-2296

Volume 81| Part 6| June 2025| Pages 338-341

https://doi.org/10.1107/S2053229625004395

Open

access

Ca(BF₄)₂·xH₂O redefined from powder diffraction as hydrogen-bonded Ca(H₂O)₄(BF₄)₂ ribbons

Armel Le Bail ^a ^*

^aLe Mans Université, Institut des Molécules et des Matériaux du Mans, CNRS UMR 6283, Av. Olivier Messiaen, 72085 Le Mans, France
^*Correspondence e-mail: [email protected]

Edited by X. Wang, Oak Ridge National Laboratory, USA (Received 1 April 2025; accepted 15 May 2025; online 19 May 2025)

The crystal structure of the calcium bis(tetrafluoroborate) hydrate Ca(BF₄)₂·xH₂O has been determined from laboratory powder diffraction data. The water molecules all belong to [CaO₄F₄] square antiprisms sharing F corners with [BF₄] tetrahedra, forming a mono-dimensional structure of infinite ribbons interconnected by H⋯F and H⋯O hydrogen bonds. No place is found for interstitial water molecules, so that the compound has to be reformulated as Ca(H₂O)₄(BF₄)₂, which is isostructural with calcium perchlorate tetrahydrate, Ca(ClO₄)₂·4H₂O.

Keywords: fluoroborate; calcium; hydrate; powder diffraction; ab initio.

CCDC reference: 2451562

1. Introduction

Calcium-based rechargeable batteries were thought to be impossible until the demonstration of the feasibility of calcium plating at moderate temperatures (Ponrouch et al., 2016 ). It was observed that optimal Ca metal deposition occurred using electrolytes containing Ca(BF₄)₂ in a mixture of ethylene carbonate and propylene carbonate at T > 75 °C. There was then a need for dry and contaminant-free Ca(BF₄)₂. Different synthetic routes were explored as alternatives to the drying of the commercial hydrated salt Ca(BF₄)₂·xH₂O which proved to be not trivial by Forero-Saboya et al. (2020 ), who proposed a value for x of 4.6, estimated by Karl–Fisher coulometer titration. However, this would correspond to 28 wt%, and a two-step decomposition is observed during thermogravimetric analysis (TGA), at 158 and 240 °C, with losses of 14.3 and 52.5 wt%, respectively. Close to two water molecules would escape first and it is believed that the remaining water persists in the solid and participates in the anion hydrolysis at temperatures above 170 °C. An older estimation for x (= 5) can be found in the PDF card 00-022-0523, dated 1969 (Kabekkodu et al., 2024 ). The present work aims at providing a definitive value for x, if any, by a successful attempt to determine the structure using the powder diffraction route since no single crystal is available.

2. Experimental

2.1. Powder diffraction

Two powder diffraction patterns of the commercial calcium bis(tetrafluoroborate) hydrate [Ca(BF₄)₂·xH₂O, Alfa Aesar] were measured using a D501 Siemens Bragg–Brentano diffractometer, the sample being either pressed or dusted on the horizontal holder, showing strong differences due to preferred orientation (see Fig. S1 in the supporting information).

2.2. Refinement

Indexing was realized using the McMaille software (Le Bail, 2004 ), leading to a triclinic cell. It was then confirmed and the intensities were extracted using the Le Bail method (Le Bail, 2005 ) implemented in the FULLPROF software (Rodríguez-Carvajal, 1993 ). The orthorhombic crystal structure of anhydrous Ca(BF₄)₂ (Jordan et al., 1975 ) has a volume close to 1100 Å³ for Z = 8; one would expect Z = 2 for the hydrated phase having V ∼ 500 Å³. The direct-space ESPOIR software (Le Bail, 2001 ) provided a starting solution when using the [CaF₈] square antiprism taken from the anhydrous phase, moved randomly in the triclinic cell together with two B and five O atoms. In the resulting model, [BF₂O₂] tetrahedra were formed interconnecting [CaF₈] antiprisms in isolated infinite ribbons. After Rietveld (1969 ) refinements from this initial model, still using FULLPROF, it was concluded that x = 4; the initial [CaF₈] block sharing four of its F corners with [BF₄] tetrahedra should be redefined as a [CaO₄F₄] square antiprism. The hydrogen-bonding scheme was then guessed observing the shortest distances between the O atoms and the terminal F atoms of the [BF₄] tetrahedra not in common with the calcium; six O—H⋯F and two O—H⋯O hydrogen bonds were disclosed. During the final refinement, soft constraints were applied on the bonding scheme and on the [BF₄] tetrahedra. Scattering factors for B³⁺ cations were taken from Olukayode et al. (2023 ). The Rietveld plot is shown in Fig. 1. Crystal data, data collection and structure refinement details are summarized in Table 1.

Table 1
Experimental details

Crystal data
Chemical formula	Ca(BF₄)₂.4H₂O
M_r	285.76
Crystal system, space group	Triclinic, P $[\overline{1}]$
Temperature (K)	293
a, b, c (Å)	5.5192 (3), 7.6756 (3), 11.6518 (5)
α, β, γ (°)	77.439 (3), 89.579 (3), 88.625 (2)
V (Å³)	481.65 (4)
Z	2
Radiation type	Cu Kα, λ = 1.540560 Å
Specimen shape, size (mm)	Flat sheet, 25 × 10

Data collection
Diffractometer	Siemens D501
Specimen mounting	Plate sample holder
Data collection mode	Reflection
Scan method	Step
2θ values (°)	2θ_min = 4.817, 2θ_max = 109.817, 2θ_step = 0.020

Refinement
R factors and goodness of fit	R_p = 6.213, R_wp = 8.419, R_exp = 1.973, R_Bragg = 3.78, χ² = 18.207
No. of parameters	115
No. of restraints	56
Computer programs: McMaille (Le Bail, 2004), ESPOIR (Le Bail, 2001, FULLPROF (Rodríguez-Carvajal, 1993), DIAMOND (Brandenburg, 1999 ) and publCIF (Westrip, 2010 ).

Figure 1
Refined diffraction pattern from laboratory data for Ca(H₂O)₄(BF₄)₂. Red dots represent the observed data and the black line represents the calculated pattern. Bragg ticks are the peak positions (main phase at the top and the CaF₂ impurity below). The bottom blue curve shows the difference between the observed and calculated patterns. A peak close to 13° (2θ) which may correspond to the (002) reflection from one tiny single crystal of the anhydrous phase in diffraction position was removed by an excluded zone (see also Fig. S1 in the supporting information, showing another pattern where there is no such peak).

3. Results and discussion

Given that all four water molecules are part of the [CaO₄F₄] square antiprisms, the compound chemistry can be reformulated as Ca(H₂O)₄(BF₄)₂ instead of the previous Ca(BF₄)₂·(x = 4)H₂O. Indeed, there is no place to acccomodate any additional water molecule. Projections of the structure along the a and b axes are shown, respectively, in Figs. 2 and 3, disclosing the complex hydrogen-bonding scheme interconnecting ribbons built from the calcium in square antiprisms sharing their F corners with [BF₄] tetrahedra (Table 2). A view in the direction of the ribbons (Fig. 4) shows how they are efficiently stacked. Six of the eight hydrogen bonds are H⋯F pointing towards the terminal F atoms of the two BF₄⁻ anions (F1, F2, F5 and F6, not shared with Ca), the remaining two hydrogen bonds are H⋯O bonds involving atoms O3 and O4. There is no intra-ribbon hydrogen bond in the structure. Each ribbon is interconnected by hydrogen bonding to four adjacent ribbons (Fig. 4), completing the structure cohesion to three dimensions. It should be noticed that this bonding scheme is an hypothesis proposed from powder diffraction data, i.e. the H atoms do not come from a Fourier difference map. Then subtleties like bifurcated bonds are hardly seen; however, bond valence calculations in the supporting material are satisfying. Trying to explain the first step in the thermogravimetric analysis (TGA) corresponding closely to the departure of two water molecules would be hazardous. Which two O atoms would first escape at 158 °C? A thermodiffractometry study would possibly reveal the existence of a dihydrate which could be formulated Ca(H₂O)₂(BF₄)₂. So the final model presented here would require either the production of large-enough single crystals or a neutron powder diffraction approach for complete confirmation, but the new Ca(H₂O)₄(BF₄)₂ formula looks likely. At least we definitely have a cell and the positions of the non-H atoms.

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H11⋯O3ⁱ	0.84 (4)	2.19 (4)	2.859 (14)	138 (4)
O1—H12⋯F2ⁱⁱ	0.83 (7)	2.17 (6)	2.925 (14)	151 (5)
O2—H21⋯O4ⁱⁱⁱ	0.86 (3)	2.23 (5)	3.015 (13)	152 (6)
O2—H22⋯F2^iv	0.88 (2)	2.18 (3)	3.041 (12)	170 (7)
O3—H31⋯F5^v	0.83 (5)	2.20 (4)	2.847 (12)	136 (4)
O3—H32⋯F6^vi	0.82 (5)	2.07 (5)	2.845 (13)	156 (6)
O4—H41⋯F1	0.85 (4)	2.16 (4)	2.848 (13)	139 (4)
O4—H42⋯F6	0.86 (6)	2.05 (7)	2.873 (13)	161 (6)
Symmetry codes: (i) ; (ii) ; (iii) ; (iv) , ; (v) ; (vi) .

Figure 2
Unit-cell projection of the Ca(H₂O)₄(BF₄)₂ structure along the a axis, showing the [BF₄] tetrahedra in blue forming infinite ribbons extending along [011] by sharing half of their F corners with the [CaO₄F₄] square antiprisms. This view shows mainly the O—H⋯F inter-ribbon bonding involving the terminal F atoms of the [BF₄] tetrahedra (not shared with Ca).

Figure 3
Unit-cell projection of the Ca(H₂O)₄(BF₄)₂ structure along the b axis, showing the intricate hydrogen-bonding scheme, with both O—H⋯F and O—H⋯O hydrogen bonds maintaining in 3D the 1D ribbons built from [CaO₄F₄] square antiprisms sharing F corners with [BF₄] tetrahedra.

Figure 4
Unit-cell projection of the Ca(H₂O)₄(BF₄)₂ structure along the [0 $[\overline{1}]$ 1] axis, showing the space between the 1D ribbons and how they are interconnected by hydrogen bonding.

Searching ultimately for related materials, the title compound was finally found to be isostructural with calcium perchlorate tetrahydrate, Ca(ClO₄)₂·4H₂O (Hennings et al., 2014a ), which is not unexpected. A search was made using the `tetrahydrate' keyword in all Acta Crystallographica articles, the calcium perchlorate tetrahydrate appeared 49th in a list of 1313 papers. The unit-cell parameters of these two compounds are not close enough for obtaining a match from the QualX search-match sofware (Altomare et al., 2015 ). Both phases present a similar hydrogen-bonding scheme. In spite of Sr(BF₄)₂ being isostructural with Ca(BF₄)₂ (Goreshnik et al., 2010 ), no strontium tetrafluoroborate tetrahydrate was found in the literature; a trihydrate was characterized recently (Charkin et al., 2023 ) and is tetragonal. Finally, Sr(ClO₄)₂·4H₂O (Hennings et al., 2014b ) is not isostructural with Ca(ClO₄)₂·4H₂O; there is no ribbon and each perchlorate anion coordinates to a dimeric unit of two Sr²⁺ cations.

Anisotropy-induced physical properties are expected from such hydrogen-bonded ribbons (Xia et al., 2003 ), which is beyond the scope of the present article, but suggests it would be of interest to look more closely at the title compound and the perchlorate analog.

4. Related literature

The following references are cited in the supporting information for this article: Brese & O'Keeffe (1991 ); Brown & Altermatt (1985 ).

Supporting information

CCDC reference: 2451562

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S2053229625004395/vx3013sup1.cif

Rietveld powder data: contains datablock I. DOI: https://doi.org/10.1107/S2053229625004395/vx3013Isup2.rtv

Comparison of powder patterns with and without preferred orientation. Search-match result. DOI: https://doi.org/10.1107/S2053229625004395/vx3013sup3.pdf

Computing details top

Calcium bis(tetrafluoroborate) tetrahydrate Ca(BF₄)₂.xH₂O top

Crystal data top

Ca(BF₄)₂.4H₂O	V = 481.65 (4) Å³
M_r = 285.76	Z = 2
Triclinic, P1	F(000) = 284
Hall symbol: -P 1	D_x = 1.970 Mg m⁻³
a = 5.5192 (3) Å	Cu Kα radiation, λ = 1.540560 Å
b = 7.6756 (3) Å	T = 293 K
c = 11.6518 (5) Å	Particle morphology: fine powder
α = 77.439 (3)°	white
β = 89.579 (3)°	flat_sheet, 25 × 10 mm
γ = 88.625 (2)°	Specimen preparation: Prepared at 293 K

Data collection top

Siemens D501 diffractometer	Data collection mode: reflection
Radiation source: X-ray tube	Scan method: step
Graphite monochromator	2θ_min = 4.817°, 2θ_max = 109.817°, 2θ_step = 0.020°
Specimen mounting: plate sample holder

Refinement top

R_p = 6.213	Profile function: pseudo-Voigt
R_wp = 8.419	115 parameters
R_exp = 1.973	56 restraints
R_Bragg = 3.78	Background function: manual
5251 data points	Preferred orientation correction: (011) direction, p = 0.939(3)
Excluded region(s): from 13.18 to 13.70 2-theta

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Ca	0.5043 (6)	0.2451 (4)	0.2506 (4)	0.0201 (11)*
B1	0.691 (3)	0.191 (2)	0.5625 (13)	0.035 (6)*
B2	0.243 (3)	0.6607 (19)	0.0545 (13)	0.035 (6)*
F1	0.5011 (13)	0.7110 (10)	0.4168 (9)	0.0358 (13)*
F2	0.0935 (10)	0.7473 (10)	0.4062 (8)	0.0358 (13)*
F3	0.3373 (14)	−0.0207 (10)	0.3737 (6)	0.0358 (13)*
F4	0.6916 (14)	0.1862 (10)	0.4474 (6)	0.0358 (13)*
F5	0.5952 (10)	0.2388 (10)	0.9128 (8)	0.0358 (13)*
F6	1.0087 (12)	0.7163 (10)	0.0753 (8)	0.0358 (13)*
F7	0.2509 (14)	0.6727 (11)	0.9334 (6)	0.0358 (13)*
F8	0.2706 (13)	0.4841 (10)	0.1123 (7)	0.0358 (13)*
O1	0.8042 (15)	0.0218 (12)	0.2488 (12)	0.0490 (17)*
O2	0.2003 (15)	0.3521 (17)	0.3682 (8)	0.0490 (17)*
O3	0.2527 (18)	0.1006 (12)	0.1263 (9)	0.0490 (17)*
O4	0.7263 (16)	0.5128 (12)	0.2635 (10)	0.0490 (17)*
H11	0.929 (6)	0.083 (5)	0.237 (4)	0.05066*
H12	0.836 (8)	−0.066 (8)	0.303 (7)	0.05066*
H21	0.075 (6)	0.370 (11)	0.324 (2)	0.05066*
H22	0.131 (7)	0.327 (14)	0.4374 (14)	0.05066*
H31	0.344 (10)	0.044 (5)	0.090 (4)	0.05066*
H32	0.184 (14)	0.179 (8)	0.077 (3)	0.05066*
H41	0.609 (6)	0.576 (5)	0.280 (4)	0.05066*
H42	0.809 (10)	0.593 (5)	0.217 (7)	0.05066*

Geometric parameters (Å, º) top

Ca—F3	2.422 (8)	F5—F8ⁱ	2.227 (11)
Ca—F4	2.468 (8)	F6—F7^viii	2.195 (11)
Ca—F7ⁱ	2.496 (8)	F6—F8^ix	2.237 (10)
Ca—F8	2.501 (8)	F7—F8^x	2.266 (10)
Ca—O1	2.357 (10)	O1—H11	0.84 (4)
Ca—O2	2.399 (11)	O1—H12	0.83 (6)
Ca—O3	2.461 (12)	O2—H21	0.86 (3)
Ca—O4	2.450 (10)	O2—H22	0.87 (2)
B1—F1ⁱ	1.336 (18)	O3—H31	0.83 (5)
B1—F2ⁱ	1.371 (18)	O3—H32	0.82 (5)
B1—F3ⁱⁱ	1.368 (16)	O4—H41	0.85 (4)
B1—F4	1.350 (17)	O4—H42	0.86 (5)
B2—F5ⁱ	1.305 (18)	H11—H12	1.34 (7)
B2—F6ⁱⁱⁱ	1.388 (18)	H21—H22	1.33 (3)
B2—F7^iv	1.394 (17)	H31—H32	1.33 (8)
B2—F8	1.382 (15)	H41—H42	1.31 (7)
F1—F2	2.261 (9)	F1—H41	2.15 (5)
F1—F3^v	2.186 (10)	F2—H12^xi	2.17 (6)
F1—F4ⁱ	2.176 (13)	F2—H22^xii	2.17 (3)
F2—F3^v	2.222 (10)	F5—H31ⁱⁱ	2.20 (4)
F2—F4ⁱ	2.239 (12)	F6—H32^xiii	2.07 (5)
F3—F4ⁱⁱ	2.199 (9)	F6—H42	2.04 (7)
F5—F6^vi	2.231 (9)	O3—H11ⁱⁱⁱ	2.19 (4)
F5—F7^vii	2.230 (12)	O4—H21^ix	2.23 (5)

F3—Ca—F4	69.9 (4)	O2—Ca—O4	85.8 (5)
F3—Ca—F7ⁱ	138.3 (5)	O3—Ca—O4	146.0 (7)
F3—Ca—F8	126.0 (5)	F1ⁱ—B1—F2ⁱ	113.3 (13)
F3—Ca—O1	75.9 (5)	F1ⁱ—B1—F3ⁱⁱ	107.9 (12)
F3—Ca—O2	74.8 (5)	F1ⁱ—B1—F4	108.2 (14)
F3—Ca—O3	71.9 (5)	F2ⁱ—B1—F3ⁱⁱ	108.5 (12)
F3—Ca—O4	141.2 (6)	F2ⁱ—B1—F4	110.8 (13)
F4—Ca—F7ⁱ	122.1 (5)	F3ⁱⁱ—B1—F4	108.1 (12)
F4—Ca—F8	140.4 (5)	F5ⁱ—B2—F6ⁱⁱⁱ	111.8 (12)
F4—Ca—O1	74.5 (5)	F5ⁱ—B2—F7^iv	111.4 (14)
F4—Ca—O2	77.0 (5)	F5ⁱ—B2—F8	111.9 (13)
F4—Ca—O3	140.9 (3)	F6ⁱⁱⁱ—B2—F7^iv	104.2 (13)
F4—Ca—O4	73.2 (4)	F6ⁱⁱⁱ—B2—F8	107.7 (12)
F7ⁱ—Ca—F8	72.9 (4)	F7^iv—B2—F8	109.5 (11)
F7ⁱ—Ca—O1	70.8 (4)	H11—O1—H12	107 (4)
F7ⁱ—Ca—O2	143.9 (6)	H21—O2—H22	100 (4)
F7ⁱ—Ca—O3	82.5 (5)	H31—O3—H32	107 (10)
F7ⁱ—Ca—O4	73.3 (5)	H41—O4—H42	101 (4)
F8—Ca—O1	140.4 (6)	O1—H11—O3^ix	138 (3)
F8—Ca—O2	74.2 (5)	F2^xiv—H12—O1	151 (5)
F8—Ca—O3	72.0 (5)	O2—H21—O4ⁱⁱⁱ	152 (3)
F8—Ca—O4	78.1 (5)	F2^xii—H22—O2	170 (2)
O1—Ca—O2	144.6 (8)	F5ⁱⁱ—H31—O3	135 (4)
O1—Ca—O3	88.3 (6)	F6^xiii—H32—O3	156 (4)
O1—Ca—O4	105.4 (6)	F1—H41—O4	139 (3)
O2—Ca—O3	101.1 (7)	F6—H42—O4	161 (4)

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) −x+1, −y, −z+1; (iii) x−1, y, z; (iv) x, y, z−1; (v) x, y+1, z; (vi) −x+2, −y+1, −z+1; (vii) −x+1, −y+1, −z+2; (viii) x+1, y, z−1; (ix) x+1, y, z; (x) x, y, z+1; (xi) x−1, y+1, z; (xii) −x, −y+1, −z+1; (xiii) −x+1, −y+1, −z; (xiv) x+1, y−1, z.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H11···O3^ix	0.84 (4)	2.19 (4)	2.859 (14)	138 (4)
O1—H12···F2^xiv	0.83 (7)	2.17 (6)	2.925 (14)	151 (5)
O2—H21···O4ⁱⁱⁱ	0.86 (3)	2.23 (5)	3.015 (13)	152 (6)
O2—H22···F2^xii	0.88 (2)	2.18 (3)	3.041 (12)	170 (7)
O3—H31···F5ⁱⁱ	0.83 (5)	2.20 (4)	2.847 (12)	136 (4)
O3—H32···F6^xiii	0.82 (5)	2.07 (5)	2.845 (13)	156 (6)
O4—H41···F1	0.85 (4)	2.16 (4)	2.848 (13)	139 (4)
O4—H42···F6	0.86 (6)	2.05 (7)	2.873 (13)	161 (6)

Symmetry codes: (ii) −x+1, −y, −z+1; (iii) x−1, y, z; (ix) x+1, y, z; (xii) −x, −y+1, −z+1; (xiii) −x+1, −y+1, −z; (xiv) x+1, y−1, z.

Valence bond analysis according to the empirical expression from Brown & Altermatt (1985), using parameters for solids from Brese & O'Keefe (1991).
References Brese, N. E. & O'Keefe, M. (1991). Acta Cryst. B47, 192–197. Brown, I. D. & Altermatt, D. (1985). Acta Cryst. B41, 244–247. top

	F1	F2	F3	F4	F5	F6	F7	F8	O1	O2	O3	O4	Σ	Σexpected
Ca			0.209	0.184			0.171	0.168	0.349	0.311	0.263	0.271	1.93	2
B1	0.862	0.784	0.790	0.830									3.27	3
B2					0.937	0.749	0.737	0.761					3.18	3
H11									0.8		0.2		1	1
H12		0.2							0.8				1	1
H21										0.8		0.2	1	1
H22		0.2								0.8			1	1
H31					0.2						0.8		1	1
H32						0.2					0.8		1	1
H41	0.2											0.8	1	1
H42						0.2						0.8	1	1
Σ	1.06	1.18	1.00	1.01	1.14	1.15	0.91	0.93	1.95	1.91	2.06	2.07
Σexpected	1	1	1	1	1	1	1	1	2	2	2	2

References

Altomare, A., Corriero, N., Cuocci, C., Falcicchio, A., Moliterni, A. & Rizzi, R. (2015). J. Appl. Cryst. 48, 598–603. Web of Science CrossRef CAS IUCr Journals Google Scholar
Brandenburg, K. (1999). DIAMOND. Crystal Impact GbR, Bonn, Germany. Google Scholar
Brese, N. E. & O'Keeffe, M. (1991). Acta Cryst. B47, 192–197. CrossRef CAS Web of Science IUCr Journals Google Scholar
Brown, I. D. & Altermatt, D. (1985). Acta Cryst. B41, 244–247. CrossRef CAS Web of Science IUCr Journals Google Scholar
Charkin, D. O., Volkov, S. N., Manelis, L. S., Gosteva, A. N., Aksenov, S. M. & Dolgikh, V. A. (2023). J. Struct. Chem. 64, 253–261. Web of Science CrossRef ICSD CAS Google Scholar
Forero-Saboya, J. D., Lozinšek, M. & Ponrouch, A. (2020). J. Power Sources Adv. 6, 100032. Google Scholar
Goreshnik, E., Vakulka, A. & Žemva, B. (2010). Acta Cryst. C66, e9. CrossRef ICSD IUCr Journals Google Scholar
Hennings, E., Schmidt, H. & Voigt, W. (2014a). Acta Cryst. E70, 489–493. CSD CrossRef IUCr Journals Google Scholar
Hennings, E., Schmidt, H. & Voigt, W. (2014b). Acta Cryst. E70, 510–514. CSD CrossRef IUCr Journals Google Scholar
Jordan, T. H., Dickens, B., Schroeder, L. W. & Brown, W. E. (1975). Acta Cryst. B31, 669–672. CrossRef ICSD CAS IUCr Journals Web of Science Google Scholar
Kabekkodu, S., Dosen, A. & Blanton, T. (2024). Powder Diffr. 39, 47–59. CrossRef CAS Google Scholar
Le Bail, A. (2001). Mater. Sci. Forum, 378–381, 65–70. Web of Science CrossRef CAS Google Scholar
Le Bail, A. (2004). Powder Diffr. 19, 249–254. Web of Science CrossRef CAS Google Scholar
Le Bail, A. (2005). Powder Diffr. 20, 316–326. Web of Science CrossRef CAS Google Scholar
Olukayode, S., Froese Fischer, C. & Volkov, A. (2023). Acta Cryst. A79, 229–245. CrossRef IUCr Journals Google Scholar
Ponrouch, A., Frontera, C., Bardé, F. & Palacín, M. R. (2016). Nat. Mater. 15, 169–172. CrossRef CAS PubMed Google Scholar
Rietveld, H. M. (1969). J. Appl. Cryst. 2, 65–71. CrossRef CAS IUCr Journals Web of Science Google Scholar
Rodríguez-Carvajal, J. (1993). Physica B, 192, 55–69. CrossRef Web of Science Google Scholar
Westrip, S. P. (2010). J. Appl. Cryst. 43, 920–925. Web of Science CrossRef CAS IUCr Journals Google Scholar
Xia, Y., Yang, P., Sun, Y., Wu, Y., Mayers, B., Gates, B., Yin, Y., Kim, F. & Yan, H. (2003). Adv. Mater. 15, 353–389. Web of Science CrossRef CAS Google Scholar

This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.