Crystal structure of disodium dicobalt(II) iron(III) tris­(orthophosphate) with an alluaudite-like structure

Bouraima, A.; Assani, A.; Saadi, M.; Makani, T.; El Ammari, L.

doi:10.1107/S2056989015007926

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Volume 71| Part 5| May 2015| Pages 558-560

https://doi.org/10.1107/S2056989015007926

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Crystal structure of disodium dicobalt(II) iron(III) tris(orthophosphate) with an alluaudite-like structure

Adam Bouraima,^a,^b ^* Abderrazzak Assani,^a Mohamed Saadi,^a Thomas Makani ^b and Lahcen El Ammari ^a

^aLaboratoire de Chimie du Solide Appliquée, Faculté des Sciences, Université Mohammed V, Avenue Ibn Battouta, BP 1014, Rabat, Morocco, and ^bDépartement de chimie, Faculté des Sciences, Université des Sciences et Techniques de Masuku, BP 943, Franceville, Gabon
^*Correspondence e-mail: adam_bouraima@yahoo.fr

Edited by I. D. Brown, McMaster University, Canada (Received 4 April 2015; accepted 21 April 2015; online 25 April 2015)

The title compound, Na₂Co₂Fe(PO₄)₃, was synthesized by a solid-state reaction. This new stoichiometric phase crystallizes in an alluaudite-like structure. In this structure, all atoms are in general positions except for four atoms which are located at the special positions of the C2/c space group. One Co atom, one P and one Na atom are all located on Wyckoff position 4e (2), while the second Na atom is located on an inversion centre 4a (-1). The other Co and Fe atoms occupy a general position with a statistical distribution. The open framework results from [(Co,Fe)₂O₁₀] units of edge-sharing [(Co,Fe)O₆] octahedra, which alternate with [CoO₆] octahedra that form infinite chains running along the [10-1] direction. These chains are linked together through PO₄ tetrahedra by the sharing of vertices so as to build layers perpendicular to [010]. The three-dimensional framework is accomplished by the stacking of these layers, leading to the formation of two types of tunnels parallel to [010] in which the Na⁺ cations are located, each cation being surrounded by eight O atoms.

Keywords: crystal structure; transition metal phosphates; solid-state reaction synthesis; Na₂Co₂Fe(PO₄)₃; alluaudite-like structure.

CCDC reference: 1060932

1. Chemical context

A particular focus of ours concerns compounds with alluaudite-type structures, and we set the objective of synthesising new transition-metal-based phosphates within the well-known alluaudite family. We are interested in this because transition-metal phosphates are of great interest with applications in several fields. Compounds belonging to the large structural family of derivatives (Moore, 1971 ) have been of continuing interest due to their structural properties, such as their open-framework architecture and their physical properties. Moreover, the flexibility of the alluaudite structure will, no doubt, permit the use of alluaudite-type phosphates for practical applications, such as corrosion inhibition, passivation of metal surfaces and catalysis (Korzenski et al., 1999 ). These materials abound in magnetic properties of metallic phosphate. Transition metals can play an important role in microporous skeletons by supplying an active catalytic site keeping the selectivity of frames (Weil et al., 2009 ). Metallic phosphates present a multitude of structural wealth which are the object of studies of catalysts (Viter & Nagornyi, 2009 ; Gao & Gao, 2005 ), ion exchange (Clearfield, 1988 ) and the positive electrode in lithium and sodium batteries (Trad et al., 2010 ). As a result of the presence of channels parallel to [100], alluaudite-type compounds exhibit electronic and/or ionic conductivity, as has been shown by Warner et al. (1993 ). In this context, we have explored A₂O–MO–P₂O₅ systems, where A is a monovalent cation and M a divalent cation. A new alluaudite structure of formula Na₂Co₂Fe(PO₄)₃ was synthesized by solid-state reaction. During our investigation of these systems, we characterized the following compounds: AgMg₃(PO₄)(HPO₄)₂ (Assani et al., 2011a ), Ag₂Ni₃(HPO₄)(PO₄)₂ (Assani et al., 2011b ) and Na₂Ni₂Fe(PO₄)₃ (Essehli et al., 2011 ). The present paper reports the solid-state synthesis and characterization of a new transition-metal phosphate, namely, Na₂Co₂Fe(PO₄)₃.

2. Structural commentary

In the refinement of the first model of this structure, we placed the Fe atom in Wyckoff position 4e and Co in the general position 8f. The results of the refinement of this model are acceptable if we disregard the high weight values. However, bond-valence-sum calculations (Brown & Altermatt, 1985 ) are not in favor of this model and, consequently, the examination of all possible models led to the best one in which half of the Co, Na, and P atoms are in Wyckoff position 4e, and the second Na atom is in position 4a of the C2/c space group, the remaining Co and Fe fulfilling the 8f site. In this case, bond-valence-sum calculations for Co2²⁺, Co1²⁺, Fe1²⁺, Na1⁺, Na2⁺, P1⁵⁺ and P2⁵⁺ ions are as expected, viz 1.78, 2.02, 2.81, 1.25, 0.94, 4.98 and 4.99 valence units, respectively.

The new phase of formula Na₂Co₂Fe(PO₄)₃ crystallizes in the alluaudite type. The structure of this compound is built up from two edge-sharing [(Co,Fe)O₆] octahedra, leading to the formation of [(Co,Fe)₂O₁₀] dimers that are connected by a common edge to [CoO₆] octahedra, as shown in Fig. 1. The linkage of alternating [CoO₆] and [(Co,Fe)₂O₁₀] octahedra leads to infinite chains along the [10 $[\overline{1}]$ ] direction. These chains held together via the vertices of the PO₄ tetrahedra in such a way as to build layers perpendicular to [010] (Fig. 2). The junction of different octahedra by common vertices of PO₄ tetrahedra form an open three-dimensional framework that delimits two types of tunnels parallel to [100] and [001] accommodating the Na⁺ cations, as shown in Fig. 3. In the tunnels, each sodium atom is surrounded by eight oxygen atoms with Na1—O and Na2—O bond lengths varying between 2.2895 (9) and 2.8754 (10) Å) and between 2.3940 (9) and 2.8513 (16) Å, respectively.

Figure 1
The principal building units in the structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level. Symmetry codes: (i) −x + $[{3\over 2}]$ , y + $[{1\over 2}]$ , −z + $[{1\over 2}]$ ; (ii) −x + $[{3\over 2}]$ , −y + $[{3\over 2}]$ , −z + 1; (iii) −x + 1, −y + 1, −z; (iv) −x + $[{3\over 2}]$ , −y + $[{3\over 2}]$ , −z; (v) −x + 1, y, −z + $[{1\over 2}]$ ; (vi) x − $[{1\over 2}]$ , −y + $[{3\over 2}]$ , z − $[{1\over 2}]$ ; (vii) x, −y + 1, z + $[{1\over 2}]$ ; (viii) x, −y + 1, z − $[{1\over 2}]$ ; (ix) −x + 2, y, −z + $[{3\over 2}]$ ; (x) −x + 2, −y + 1, −z + 1; (xi) x + $[{1\over 2}]$ , −y + $[{1\over 2}]$ , z + $[{1\over 2}]$ ; (xii) −x + $[{3\over 2}]$ , −y + $[{1\over 2}]$ , −z + 1.

Figure 2
A layer perpendicular to the b axis, resulting from the chains connected via the vertices of the PO₄ tetrahedra.

Figure 3
Polyhedral representation of Na₂Co₂Fe(PO₄)₃ showing the tunnels running along the [001] direction.

3. Synthesis and crystallization

Na₂Co₂Fe(PO₄)₃ was synthesized by a solid-state reaction by mixing the precursors of sodium (Na₂CO₃), cobalt (CoCO₃), iron (Fe₂O₃) and phosphoric acid 85% wt. The various precursors were taken in the molar ratio Na:Co:Fe:P = 2:2:1:3.

After different heat treatments in a platinum crucible up to 873 K, the reaction mixture was heated to the melting point of 1000 K. The molten product was then cooled to room temperature at a rate of 5 K h⁻¹. The resulting product contained brown crystals of a suitable size for the X-ray diffraction study.

4. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. The same x, y and z parameters and anisotropic displacement parameters are used for Co1 and Fe1 sharing the same site. Three reflections, (042), (110) and ( $[\overline{2}]$ 42), probably affected by the beam-stop, were removed during the last refinement cycle. The highest peak and the deepest hole in the final Fourier map are at 0.40 Å and 0.42 Å from Na1 and Na2, respectively.

Table 1
Experimental details

Crystal data
Chemical formula	Na₂Co₂Fe(PO₄)₃
M_r	504.60
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	296
a, b, c (Å)	11.7106 (6), 12.4083 (7), 6.4285 (3)
β (°)	113.959 (2)
V (Å³)	853.63 (8)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	6.26
Crystal size (mm)	0.31 × 0.25 × 0.19

Data collection
Diffractometer	Bruker X8 APEX
Absorption correction	Multi-scan (SADABS; Bruker, 2009 )
T_min, T_max	0.504, 0.748
No. of measured, independent and observed [I > 2σ(I)] reflections	15289, 1882, 1807
R_int	0.030
(sin θ/λ)_max (Å⁻¹)	0.806

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.016, 0.046, 1.10
No. of reflections	1879
No. of parameters	95
Δρ_max, Δρ_min (e Å⁻³)	0.70, −0.92
Computer programs: APEX2 and SAINT (Bruker, 2009), SHELXS97 and SHELXL97 (Sheldrick, 2008 ), ORTEP-3 for Windows (Farrugia, 2012 ), DIAMOND (Brandenburg, 2006 ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC reference: 1060932

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989015007926/br2248sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989015007926/br2248Isup2.hkl

checkCIF report

Computing details top

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Disodium dicobalt(II) iron(III) tris(orthophosphate) top

Crystal data top

Na₂Co₂Fe(PO₄)₃	F(000) = 972
M_r = 504.60	D_x = 3.926 Mg m⁻³
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -c 2yc	Cell parameters from 1882 reflections
a = 11.7106 (6) Å	θ = 2.5–34.9°
b = 12.4083 (7) Å	µ = 6.26 mm⁻¹
c = 6.4285 (3) Å	T = 296 K
β = 113.959 (2)°	Block, brown
V = 853.63 (8) Å³	0.31 × 0.25 × 0.19 mm
Z = 4

Data collection top

Bruker X8 APEX diffractometer	1882 independent reflections
Radiation source: fine-focus sealed tube	1807 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.030
φ and ω scans	θ_max = 34.9°, θ_min = 2.5°
Absorption correction: multi-scan (SADABS; Bruker, 2009)	h = −18→18
T_min = 0.504, T_max = 0.748	k = −20→20
15289 measured reflections	l = −9→10

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.016	w = 1/[σ²(F_o²) + (0.026P)² + 1.033P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.046	(Δ/σ)_max = 0.002
S = 1.10	Δρ_max = 0.70 e Å⁻³
1879 reflections	Δρ_min = −0.92 e Å⁻³
95 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.0049 (3)

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. Refinement of F² against all reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on all data will be even larger.

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

	x	y	z	U_iso*/U_eq	Occ. (<1)
Fe1	0.717910 (14)	0.842242 (12)	0.13094 (2)	0.00487 (5)	0.50
Co1	0.717910 (14)	0.842242 (12)	0.13094 (2)	0.00487 (5)	0.50
Co2	0.5000	0.731171 (18)	0.2500	0.00645 (5)
P1	0.76483 (3)	0.60996 (2)	0.37608 (4)	0.00406 (6)
P2	0.5000	0.29046 (3)	0.2500	0.00393 (7)
Na1	0.5000	0.5000	0.0000	0.01623 (17)
Na2	1.0000	0.48710 (12)	0.7500	0.0343 (3)
O1	0.77862 (8)	0.67773 (7)	0.18650 (14)	0.00805 (14)
O2	0.83828 (8)	0.66574 (7)	0.60820 (14)	0.00755 (14)
O3	0.82670 (9)	0.49990 (7)	0.38761 (16)	0.00954 (15)
O4	0.62676 (8)	0.60150 (7)	0.32737 (15)	0.00871 (14)
O5	0.60276 (8)	0.36657 (7)	0.25279 (15)	0.00938 (15)
O6	0.45930 (8)	0.21880 (7)	0.03503 (13)	0.00683 (13)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Fe1	0.00449 (7)	0.00506 (7)	0.00514 (7)	−0.00034 (4)	0.00203 (5)	−0.00037 (4)
Co1	0.00449 (7)	0.00506 (7)	0.00514 (7)	−0.00034 (4)	0.00203 (5)	−0.00037 (4)
Co2	0.00659 (9)	0.00646 (9)	0.00728 (9)	0.000	0.00381 (7)	0.000
P1	0.00506 (11)	0.00343 (11)	0.00348 (10)	−0.00004 (8)	0.00150 (8)	−0.00003 (7)
P2	0.00357 (15)	0.00423 (15)	0.00352 (14)	0.000	0.00094 (11)	0.000
Na1	0.0262 (4)	0.0032 (3)	0.0068 (3)	0.0017 (3)	−0.0061 (3)	0.0008 (2)
Na2	0.0187 (5)	0.0569 (8)	0.0218 (5)	0.000	0.0026 (4)	0.000
O1	0.0094 (3)	0.0097 (3)	0.0052 (3)	−0.0011 (3)	0.0031 (3)	0.0014 (3)
O2	0.0097 (3)	0.0073 (3)	0.0049 (3)	−0.0018 (3)	0.0021 (3)	−0.0015 (2)
O3	0.0113 (4)	0.0061 (3)	0.0109 (3)	0.0026 (3)	0.0043 (3)	−0.0012 (3)
O4	0.0057 (3)	0.0080 (3)	0.0124 (3)	−0.0002 (3)	0.0037 (3)	0.0002 (3)
O5	0.0063 (3)	0.0081 (3)	0.0124 (3)	−0.0022 (3)	0.0024 (3)	0.0024 (3)
O6	0.0065 (3)	0.0089 (3)	0.0047 (3)	−0.0008 (3)	0.0019 (2)	−0.0019 (2)

Geometric parameters (Å, º) top

Fe1—O5ⁱ	1.9456 (9)	P2—O6^v	1.5468 (8)
Fe1—O3ⁱ	2.0158 (9)	P2—O6	1.5468 (8)
Fe1—O2ⁱⁱ	2.0374 (9)	Na1—O5ⁱⁱⁱ	2.2895 (9)
Fe1—O6ⁱⁱⁱ	2.0543 (9)	Na1—O5	2.2895 (9)
Fe1—O1^iv	2.0724 (8)	Na1—O4ⁱⁱⁱ	2.3835 (9)
Fe1—O1	2.1434 (9)	Na1—O4	2.3836 (9)
Co2—O4^v	2.1072 (9)	Na1—O4^viii	2.5217 (9)
Co2—O4	2.1072 (9)	Na1—O4^v	2.5218 (9)
Co2—O2ⁱⁱ	2.1567 (9)	Na1—O5^v	2.8754 (10)
Co2—O2^vi	2.1568 (9)	Na1—O5^viii	2.8754 (10)
Co2—O6^vii	2.1632 (8)	Na2—O3^ix	2.3940 (9)
Co2—O6ⁱⁱⁱ	2.1632 (8)	Na2—O3	2.3940 (9)
P1—O4	1.5206 (9)	Na2—O3^x	2.5269 (10)
P1—O3	1.5336 (9)	Na2—O3^vii	2.5269 (10)
P1—O1	1.5422 (9)	Na2—O2^ix	2.8158 (15)
P1—O2	1.5502 (9)	Na2—O2	2.8158 (15)
P2—O5^v	1.5240 (9)	Na2—O6^xi	2.8513 (16)
P2—O5	1.5241 (9)	Na2—O6^xii	2.8513 (16)

O5ⁱ—Fe1—O3ⁱ	94.91 (4)	O5—Na1—O4^viii	73.59 (3)
O5ⁱ—Fe1—O2ⁱⁱ	110.51 (4)	O4ⁱⁱⁱ—Na1—O4^viii	67.32 (4)
O3ⁱ—Fe1—O2ⁱⁱ	86.18 (4)	O4—Na1—O4^viii	112.68 (4)
O5ⁱ—Fe1—O6ⁱⁱⁱ	164.12 (4)	O5ⁱⁱⁱ—Na1—O4^v	73.59 (3)
O3ⁱ—Fe1—O6ⁱⁱⁱ	98.29 (4)	O5—Na1—O4^v	106.41 (3)
O2ⁱⁱ—Fe1—O6ⁱⁱⁱ	79.27 (3)	O4ⁱⁱⁱ—Na1—O4^v	112.68 (4)
O5ⁱ—Fe1—O1^iv	86.97 (4)	O4—Na1—O4^v	67.32 (4)
O3ⁱ—Fe1—O1^iv	99.56 (4)	O4^viii—Na1—O4^v	180.0
O2ⁱⁱ—Fe1—O1^iv	161.21 (4)	O5ⁱⁱⁱ—Na1—O5^v	126.25 (4)
O6ⁱⁱⁱ—Fe1—O1^iv	82.19 (3)	O5—Na1—O5^v	53.75 (4)
O5ⁱ—Fe1—O1	81.40 (4)	O4ⁱⁱⁱ—Na1—O5^v	86.18 (3)
O3ⁱ—Fe1—O1	174.04 (4)	O4—Na1—O5^v	93.82 (3)
O2ⁱⁱ—Fe1—O1	90.73 (3)	O4^viii—Na1—O5^v	114.14 (3)
O6ⁱⁱⁱ—Fe1—O1	86.11 (3)	O4^v—Na1—O5^v	65.86 (3)
O1^iv—Fe1—O1	84.97 (3)	O5ⁱⁱⁱ—Na1—O5^viii	53.75 (4)
O4^v—Co2—O4	80.44 (5)	O5—Na1—O5^viii	126.25 (4)
O4^v—Co2—O2ⁱⁱ	165.05 (3)	O4ⁱⁱⁱ—Na1—O5^viii	93.82 (3)
O4—Co2—O2ⁱⁱ	86.54 (3)	O4—Na1—O5^viii	86.18 (3)
O4^v—Co2—O2^vi	86.54 (3)	O4^viii—Na1—O5^viii	65.86 (3)
O4—Co2—O2^vi	165.05 (3)	O4^v—Na1—O5^viii	114.14 (3)
O2ⁱⁱ—Co2—O2^vi	107.25 (5)	O5^v—Na1—O5^viii	180.0
O4^v—Co2—O6^vii	92.44 (3)	O3^ix—Na2—O3	172.39 (8)
O4—Co2—O6^vii	113.30 (3)	O3^ix—Na2—O3^x	81.52 (3)
O2ⁱⁱ—Co2—O6^vii	85.96 (3)	O3—Na2—O3^x	97.99 (3)
O2^vi—Co2—O6^vii	74.34 (3)	O3^ix—Na2—O3^vii	97.99 (3)
O4^v—Co2—O6ⁱⁱⁱ	113.30 (3)	O3—Na2—O3^vii	81.52 (3)
O4—Co2—O6ⁱⁱⁱ	92.44 (3)	O3^x—Na2—O3^vii	172.68 (8)
O2ⁱⁱ—Co2—O6ⁱⁱⁱ	74.34 (3)	O3^ix—Na2—O2^ix	55.93 (3)
O2^vi—Co2—O6ⁱⁱⁱ	85.96 (3)	O3—Na2—O2^ix	117.11 (5)
O6^vii—Co2—O6ⁱⁱⁱ	146.65 (5)	O3^x—Na2—O2^ix	62.15 (3)
O4—P1—O3	112.98 (5)	O3^vii—Na2—O2^ix	111.51 (5)
O4—P1—O1	108.59 (5)	O3^ix—Na2—O2	117.11 (5)
O3—P1—O1	108.95 (5)	O3—Na2—O2	55.93 (3)
O4—P1—O2	110.92 (5)	O3^x—Na2—O2	111.51 (5)
O3—P1—O2	106.53 (5)	O3^vii—Na2—O2	62.15 (3)
O1—P1—O2	108.78 (5)	O2^ix—Na2—O2	76.15 (5)
O5^v—P2—O5	103.42 (7)	O3^ix—Na2—O6^xi	116.10 (5)
O5^v—P2—O6^v	108.79 (5)	O3—Na2—O6^xi	71.28 (4)
O5—P2—O6^v	112.97 (5)	O3^x—Na2—O6^xi	83.54 (4)
O5^v—P2—O6	112.97 (5)	O3^vii—Na2—O6^xi	103.11 (4)
O5—P2—O6	108.79 (5)	O2^ix—Na2—O6^xi	145.12 (3)
O6^v—P2—O6	109.82 (7)	O2—Na2—O6^xi	126.19 (2)
O5ⁱⁱⁱ—Na1—O5	180.0	O3^ix—Na2—O6^xii	71.28 (4)
O5ⁱⁱⁱ—Na1—O4ⁱⁱⁱ	78.23 (3)	O3—Na2—O6^xii	116.10 (5)
O5—Na1—O4ⁱⁱⁱ	101.77 (3)	O3^x—Na2—O6^xii	103.11 (4)
O5ⁱⁱⁱ—Na1—O4	101.77 (3)	O3^vii—Na2—O6^xii	83.54 (4)
O5—Na1—O4	78.23 (3)	O2^ix—Na2—O6^xii	126.19 (2)
O4ⁱⁱⁱ—Na1—O4	180.0	O2—Na2—O6^xii	145.12 (3)
O5ⁱⁱⁱ—Na1—O4^viii	106.41 (3)	O6^xi—Na2—O6^xii	52.71 (4)

Symmetry codes: (i) −x+3/2, y+1/2, −z+1/2; (ii) −x+3/2, −y+3/2, −z+1; (iii) −x+1, −y+1, −z; (iv) −x+3/2, −y+3/2, −z; (v) −x+1, y, −z+1/2; (vi) x−1/2, −y+3/2, z−1/2; (vii) x, −y+1, z+1/2; (viii) x, −y+1, z−1/2; (ix) −x+2, y, −z+3/2; (x) −x+2, −y+1, −z+1; (xi) x+1/2, −y+1/2, z+1/2; (xii) −x+3/2, −y+1/2, −z+1.

Acknowledgements

The authors thank the Unit of Support for Technical and Scientific Research (UATRS, CNRST) for the X-ray measurements and Mohammed V University, Rabat, Morocco, for financial support.

References

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