Pirquitasite, Ag2ZnSnS4

Schumer, B.N.; Downs, R.T.; Domanik, K.J.; Andrade, M.B.; Origlieri, M.J.

doi:10.1107/S1600536813001013

inorganic compounds

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Volume 69| Part 2| February 2013| Pages i8-i9

doi:10.1107/S1600536813001013

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Pirquitasite, Ag₂ZnSnS₄

Benjamin N. Schumer,^a ^* Robert T. Downs,^a Kenneth J. Domanik,^b Marcelo B Andrade ^a and Marcus J. Origlieri ^a

^aDepartment of Geosciences, University of Arizona, Tucson, Arizona 85721-0077, USA, and ^bLunar and Planetary Laboratory, University of Arizona, 1629 E. University Boulevard, Tucson, AZ 85721-0092, USA
^*Correspondence e-mail: bschumer@email.arizona.edu

(Received 19 December 2012; accepted 10 January 2013; online 19 January 2013)

Pirquitasite, ideally Ag₂ZnSnS₄ (disilver zinc tin tetrasulfide), exhibits tetragonal symmetry and is a member of the stannite group that has the general formula A₂BCX₄, with A = Ag, Cu; B = Zn, Cd, Fe, Cu, Hg; C = Sn, Ge, Sb, As; and X = S, Se. In this study, single-crystal X-ray diffraction data are used to determine the structure of pirquitasite from a twinned crystal from the type locality, the Pirquitas deposit, Jujuy Province, Argentina, with anisotropic displacement parameters for all atoms, and a measured composition of (Ag_1.87Cu_0.13)(Zn_0.61Fe_0.36Cd_0.03)SnS₄. One Ag atom is located on Wyckoff site Wyckoff 2a (symmetry -4..), the other Ag atom is statistically disordered with minor amounts of Cu and is located on 2c (-4..), the (Zn, Fe, Cd) site on 2d (-4..), Sn on 2b (-4..), and S on general site 8g. This is the first determination of the crystal structure of pirquitasite, and our data indicate that the space group of pirquitasite is I-4, rather than I-42m as previously suggested. The structure was refined under consideration of twinning by inversion [twin ratio of the components 0.91 (6):0.09 (6)].

Related literature

For related structures in the stannite–kesterite series, see: Orlova (1956 ); Hall et al. (1978 ); Kissin & Owens (1979 ); Bonazzi et al. (2003 ). For previous work on hocartite and pirquitasite, see: Johan & Picot (1982 ). For details on synthetic stannite group phases, see: Salomé et al. (2012 ); Sasamura et al. (2012 ); Tsuji et al. 2010 ). For other stannite group minerals, see: Chen et al. (1998 ); Frenzel (1959 ); Garin & Parthé (1972 ); Johan et al. (1971 ); Kaplunnik et al. (1977 ); Kissin & Owens (1989 ); Marumo & Nowaki (1967 ); Murciego et al. (1999 ); Szymański (1978 ); Wintenberger (1979 ).

Experimental

Crystal data

(Ag_1.87Cu_0.13)(Zn_0.61Fe_0.36Cd_0.03)SnS₄
M_r = 520.26
Tetragonal, $[I \overline 4]$
a = 5.7757 (12) Å
c = 10.870 (2) Å
V = 362.60 (13) Å³
Z = 2
Mo Kα radiation
μ = 12.58 mm⁻¹
T = 293 K
0.05 × 0.05 × 0.04 mm

Data collection

Bruker APEXII CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 2005 ) T_min = 0.572, T_max = 0.633
1312 measured reflections
575 independent reflections
570 reflections with I > 2σ(I)
R_int = 0.013

Refinement

R[F² > 2σ(F²)] = 0.027
wR(F²) = 0.070
S = 1.17
575 reflections
24 parameters
4 restraints
Δρ_max = 1.05 e Å⁻³
Δρ_min = −0.87 e Å⁻³
Absolute structure: Flack (1983 )
Flack parameter: 0.91 (6)

Table 1
Table 1. Minerals of the Stannite Group

Mineral	Formula	Space Group	Reference
Stannite	Cu₂FeSnS₄	I $[\overline{4}]$ 2m	Hall et al. (1978)
Hocartite	Ag₂FeSnS₄	I $[\overline{4}]$ 2m	Johan & Picot (1982)
Kuramite	Cu₂¹⁺Cu²⁺SnS₄	I $[\overline{4}]$ 2m	Chen et al. (1998)
Černyite	Cu₂CdSnS₄	I $[\overline{4}]$ 2m	Szymański (1978)
Velikite	Cu₂HgSnS₄	I $[\overline{4}]$ 2m	Kaplunnik et al. (1977)
Famatinite	Cu₂¹⁺Cu²⁺SbS₄	I $[\overline{4}]$ 2m	Garin & Parthé (1972)
Luzonite	Cu₂¹⁺Cu²⁺AsS₄	I $[\overline{4}]$ 2m	Marumo & Nowaki (1967)
Barquillite	Cu₂(Cd,Fe²⁺)GeS₄	I $[\overline{4}]$ 2m	Murciego et al. (1999)
Briartite	Cu₂FeGeS₄	I $[\overline{4}]$ 2m	Wintenberger (1979)
Permingeatite	Cu₂¹⁺Cu²⁺SbSe₄	I $[\overline{4}]$ 2m	Johan et al. (1971)
Kesterite	Cu₂ZnSnS₄	I $[\overline{4}]$	Kissin & Owens (1979)
Ferrokesterite	Cu₂(Fe,Zn)SnS₄	I $[\overline{4}]$	Kissin & Owens (1989)
Pirquitasite	Ag₂ZnSnS₄	I $[\overline{4}]$	This study
Idaite	Cu₂⁺Cu²⁺FeS₄	Unknown	Frenzel (1959)

Data collection: APEX2 (Bruker, 2004 ); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XtalDraw (Downs & Hall-Wallace, 2003 ); software used to prepare material for publication: publCIF (Westrip, 2010 ).

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536813001013/br2219sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536813001013/br2219Isup2.hkl

checkCIF report

Comment top

Pirquitasite is a member of the stannite group of tetragonal sulfides, which exhibit space group I42m or I4, and is an ordered derivative of the sphalerite structure (Johan and Picot, 1982). The stannite group currently contains thirteen species (Table 1), of which only kësterite, ferrokësterite, and pirquitasite are known to display space group I4. Synthetic sulfides with stannite type structures are utilized as the light absorber layer in photovoltaic cells (e.g. Salomé et al. 2012, Sasamura et al. 2012, Tsuji et al. 2010).

Pirquitasite was first described by Johan and Picot (1982), from the Pirquitas deposit, Argentina, as a silver zinc tin sulfide with ideal chemical formula Ag₂ZnSnS₄ and a stannite-like structure. An extensive solid solution between hocartite (Ag₂FeSnS₄) and pirquitasite was described by Johan and Picot (1982). Because of the solid solution and the I42m symmetry attributed to hocartite, Johan and Picot (1982) proposed that pirquitasite also exhibits I42m symmetry.

The structure was refined using both I42m and I4, with the R factor for I4 (R = 0.027) significantly lower than for I42m (R = 0.051). The structure of pirquitasite is a derivative of the cubic sphalerite structure that displays cubic closest packed (CCP) layers of S stacked along [111]. Because pirquitasite has a doubled c cell dimension, its stacking direction is [221]. Half of the tetrahedral sites are occupied by Ag, (Zn,Fe), and Sn cations, forming metal layers described by Hall et al. (1978), and it is the arrangement of Ag, (Zn,Fe), and Sn within these layers that differentiates the I4 kësterite structure from the I42m stannite structure.

Stannite and kësterite were originally recognized as distinct species because of different Fe—Zn compositional ratios and different optical properties (Orlova, 1956; Hall et al. 1978). Structural and chemical analyses by Hall et al. (1978) and Kissin and Owens (1979) not only showed a miscibility gap between the pure Fe end-member stannite and the pure Zn end-member kësterite, but found the two minerals differed in symmetry from I42m (stannite) to I4 (kësterite). In I42m, Cu atoms are ordered to the Wyckoff 4d site, (Fe,Zn) atoms are ordered to Wyckoff 2a, Sn is ordered to 2b (Hall et al. 1978). For comparison, the I4 symmetry has Cu atoms ordered to two sites: 2a and 2c, (Zn,Fe) ordered to 2d, Sn ordered to 2b (Hall et al. 1978). As pointed out by Hall et al. (1978), two distinct metal layers perpendicular to [001] result from this ordering in each mineral. Stannite exhibits one layer of Cu atoms only, with the other layer consisting of ordered Fe and Sn atoms, while kësterite exhibits one layer of ordered Cu and Sn atoms and one layer of ordered Zn and Cu atoms (Hall et al. 1978). This is illustrated for pirquitasite versus stannite in Fig. 1, which shows the pirquitasite structure (Fig. 1a) with one layer containing ordered Ag and Sn, the second containing ordered Zn and Ag. For comparison, the two stannite metal layers consist of one layer of Fe and Sn atoms and a second layer containing only Cu atoms (Fig. 1 b). The Ag—Sn layers in pirquitasite and Fe—Sn layers in stannite are ordered identically: Ag—Sn—Ag—Sn and Fe—Sn—Fe—Sn respectively when viewed along (100).

The mineral hocartite (tetragonal Ag₂FeSnS₄) is reported to exhibit space group I42m (Johan and Picot, 1982), but its structure is as yet unreported. It is likely that the hocartite-pirquitasite series follows the same systematics as the stannite-kësterite series.

An interesting feature is the distortion displayed by the AgS₄ tetrahedra, with tetrahedral angle variance of 8.86° displayed by Ag1S₄ and 25.40° displayed by Ag2S₄. M-S bond lengths are 2.539 Å and 2.497 Å for the Ag1S₄ and Ag2S₄ tetrahedra, respectively. As our sample contains approximately 13% apfu Cu, this Cu appears to be located in the Ag2 site because the bond lengths are smaller and the tetrahedron can accomodate the distortion. Bond valence calculations gave sums of 1.28 valence units (VU) and 1.35 VU for Ag1 and Ag2, respectively, corroborating that Cu is ordered to the Ag2 site. In a study of the mechanism of incorporation of Cu, Fe, and Zn in the stannite-kësterite series, Bonazzi et al. (2003) studied synthetic crystals, quenched from 1023 Kelvin, of composition Cu₂Fe_1-_XZn_XS₄ (X = 0, 1/5, 1/2, 0.7, 0.8, 1), which showed decreasing tetrahedral angle distortion with increasing Zn content across the stannite-kësterite compositions.

Related literature top

For related structures in the stannite–kësterite series, see: Orlova (1956); Hall et al. (1978); Kissin & Owens (1979); Bonazzi et al. (2003). For previous work on hocartite and pirquitasite, see: Johan & Picot (1982). For details on synthetic stannite group phases, see: Salomé et al. (2012); Sasamura et al. (2012); Tsuji et al. 2010). For other stannite group minerals, see: Chen et al. (1998); Frenzel (1959); Garin & Parthé (1972); Johan et al. (1971); Kaplunnik et al. (1977); Kissin & Owens (1989); Marumo & Nowaki (1967); Murciego et al. (1999); Szymański (1978); Wintenberger (1979).

Experimental top

The pirquitasite specimen used in this study comes from the type locality, the Pirquitas deposit, Jujuy Province, Argentina and is in the collection of the RRUFF project (http://rruff.info/R061016). The chemical composition, (Ag_1.87Cu_0.13)(Zn_0.61Fe_0.36Cd_0.03)SnS₄, was determined with a CAMECA SX100 electron microprobe. The composition was normalized to four cations.

Computing details top

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XtalDraw (Downs & Hall-Wallace, 2003); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top

Fig. 1. Diagrams of displacement ellipsoids drawn at the 99.999% level for (a) pirquitasite and (b) stannite viewed along (100), with [001] vertical. The two types of metal layers are stacked along [001].

Disilver zinc tin tetrasulfide top

Crystal data top

(Ag_1.87Cu_0.13)(Zn_0.61Fe_0.36Cd_0.03)SnS₄	D_x = 4.765 Mg m⁻³
M_r = 520.26	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I4	Cell parameters from 527 reflections
Hall symbol: I -4	θ = 6.3–32.3°
a = 5.7757 (12) Å	µ = 12.58 mm⁻¹
c = 10.870 (2) Å	T = 293 K
V = 362.60 (13) Å³	Cuboid, grey
Z = 2	0.05 × 0.05 × 0.04 mm
F(000) = 470

Data collection top

Bruker APEXII CCD area-detector diffractometer	575 independent reflections
Radiation source: fine-focus sealed tube	570 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.013
ϕ and ω scan	θ_max = 32.0°, θ_min = 3.8°
Absorption correction: multi-scan (SADABS; Sheldrick, 2005)	h = −4→8
T_min = 0.572, T_max = 0.633	k = −8→7
1312 measured reflections	l = −16→12

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.0272P)² + 2.1498P] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.027	(Δ/σ)_max < 0.001
wR(F²) = 0.070	Δρ_max = 1.05 e Å⁻³
S = 1.17	Δρ_min = −0.87 e Å⁻³
575 reflections	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
24 parameters	Extinction coefficient: 0.0061 (6)
4 restraints	Absolute structure: Flack (1983)
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.91 (6)

Crystal data top

(Ag_1.87Cu_0.13)(Zn_0.61Fe_0.36Cd_0.03)SnS₄	Z = 2
M_r = 520.26	Mo Kα radiation
Tetragonal, I4	µ = 12.58 mm⁻¹
a = 5.7757 (12) Å	T = 293 K
c = 10.870 (2) Å	0.05 × 0.05 × 0.04 mm
V = 362.60 (13) Å³

Data collection top

Bruker APEXII CCD area-detector diffractometer	575 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 2005)	570 reflections with I > 2σ(I)
T_min = 0.572, T_max = 0.633	R_int = 0.013
1312 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.027	4 restraints
wR(F²) = 0.070	Δρ_max = 1.05 e Å⁻³
S = 1.17	Δρ_min = −0.87 e Å⁻³
575 reflections	Absolute structure: Flack (1983)
24 parameters	Absolute structure parameter: 0.91 (6)

Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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)
Ag1	0.0000	0.0000	0.0000	0.0364 (4)
Ag2	0.0000	0.5000	0.2500	0.0301 (6)	0.87
Cu	0.0000	0.5000	0.2500	0.0301 (6)	0.13
Zn	0.5000	0.0000	0.2500	0.0220 (6)	0.61
Fe	0.5000	0.0000	0.2500	0.0220 (6)	0.36
Cd	0.5000	0.0000	0.2500	0.0220 (6)	0.03
Sn	0.5000	0.5000	0.0000	0.01176 (18)
S	0.7325 (3)	0.2526 (4)	0.12847 (11)	0.0214 (3)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ag1	0.0360 (5)	0.0360 (5)	0.0372 (4)	0.000	0.000	0.000
Ag2	0.0274 (7)	0.0274 (7)	0.0355 (9)	0.000	0.000	0.000
Cu	0.0274 (7)	0.0274 (7)	0.0355 (9)	0.000	0.000	0.000
Zn	0.0248 (8)	0.0248 (8)	0.0163 (9)	0.000	0.000	0.000
Fe	0.0248 (8)	0.0248 (8)	0.0163 (9)	0.000	0.000	0.000
Cd	0.0248 (8)	0.0248 (8)	0.0163 (9)	0.000	0.000	0.000
Sn	0.0114 (2)	0.0114 (2)	0.0125 (3)	0.000	0.000	0.000
S	0.0250 (6)	0.0212 (6)	0.0181 (6)	0.0053 (5)	−0.0023 (5)	0.0044 (5)

Geometric parameters (Å, º) top

Ag1—Sⁱ	2.5430 (17)	Zn—S^iv	2.383 (2)
Ag1—Sⁱⁱ	2.5430 (17)	Zn—S^viii	2.383 (2)
Ag1—Sⁱⁱⁱ	2.5430 (17)	Zn—S	2.383 (2)
Ag1—S^iv	2.5430 (17)	Zn—S^vii	2.383 (2)
Ag2—Sⁱⁱⁱ	2.485 (2)	Sn—Sⁱⁱ	2.4070 (16)
Ag2—S^v	2.485 (2)	Sn—S	2.4070 (16)
Ag2—S^vi	2.485 (2)	Sn—S^v	2.4070 (16)
Ag2—S^vii	2.485 (2)	Sn—S^ix	2.4070 (16)

Sⁱ—Ag1—Sⁱⁱ	113.39 (6)	S^iv—Zn—S^viii	107.90 (4)
Sⁱ—Ag1—Sⁱⁱⁱ	107.55 (3)	S^iv—Zn—S	112.66 (8)
Sⁱⁱ—Ag1—Sⁱⁱⁱ	107.55 (3)	S^viii—Zn—S	107.90 (4)
Sⁱ—Ag1—S^iv	107.55 (3)	S^iv—Zn—S^vii	107.90 (4)
Sⁱⁱ—Ag1—S^iv	107.55 (3)	S^viii—Zn—S^vii	112.66 (8)
Sⁱⁱⁱ—Ag1—S^iv	113.39 (6)	S—Zn—S^vii	107.90 (4)
Sⁱⁱⁱ—Ag2—S^v	115.77 (7)	Sⁱⁱ—Sn—S	109.67 (4)
Sⁱⁱⁱ—Ag2—S^vi	106.42 (3)	Sⁱⁱ—Sn—S^v	109.67 (4)
S^v—Ag2—S^vi	106.42 (3)	S—Sn—S^v	109.08 (7)
Sⁱⁱⁱ—Ag2—S^vii	106.42 (3)	Sⁱⁱ—Sn—S^ix	109.08 (7)
S^v—Ag2—S^vii	106.42 (3)	S—Sn—S^ix	109.67 (4)
S^vi—Ag2—S^vii	115.77 (7)	S^v—Sn—S^ix	109.67 (4)

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

Experimental details

Crystal data
Chemical formula	(Ag_1.87Cu_0.13)(Zn_0.61Fe_0.36Cd_0.03)SnS₄
M_r	520.26
Crystal system, space group	Tetragonal, I4
Temperature (K)	293
a, c (Å)	5.7757 (12), 10.870 (2)
V (Å³)	362.60 (13)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	12.58
Crystal size (mm)	0.05 × 0.05 × 0.04

Data collection
Diffractometer	Bruker APEXII CCD area-detector diffractometer
Absorption correction	Multi-scan (SADABS; Sheldrick, 2005)
T_min, T_max	0.572, 0.633
No. of measured, independent and observed [I > 2σ(I)] reflections	1312, 575, 570
R_int	0.013
(sin θ/λ)_max (Å⁻¹)	0.746

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.027, 0.070, 1.17
No. of reflections	575
No. of parameters	24
No. of restraints	4
Δρ_max, Δρ_min (e Å⁻³)	1.05, −0.87
Absolute structure	Flack (1983)
Absolute structure parameter	0.91 (6)

Computer programs: APEX2 (Bruker, 2004), SAINT (Bruker, 2004), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), XtalDraw (Downs & Hall-Wallace, 2003), publCIF (Westrip, 2010).

Table 1. Minerals of the Stannite Group top

Mineral	Formula	Space Group	Reference
Stannite	Cu₂FeSnS₄	I42m	Hall et al. (1978)
Hocartite	Ag₂FeSnS₄	I42m	Johan & Picot (1982)
Kuramite	Cu₂¹⁺Cu²⁺SnS₄	I42m	Chen et al. (1998)
Černyite	Cu₂CdSnS₄	I42m	Szymański (1978)
Velikite	Cu₂HgSnS₄	I42m	Kaplunnik et al. (1977)
Famatinite	Cu₂¹⁺Cu²⁺SbS₄	I42m	Garin & Parthé (1972)
Luzonite	Cu₂¹⁺Cu²⁺AsS₄	I42m	Marumo & Nowaki (1967)
Barquillite	Cu₂(Cd,Fe²⁺)GeS₄	I42m	Murciego et al. (1999)
Briartite	Cu₂FeGeS₄	I42m	Wintenberger (1979)
Permingeatite	Cu₂¹⁺Cu²⁺SbSe₄	I42m	Johan et al. (1971)
Kesterite	Cu₂ZnSnS₄	I4	Kissin & Owens (1979)
Ferrokesterite	Cu₂(Fe,Zn)SnS₄	I4	Kissin & Owens (1989)
Pirquitasite	Ag₂ZnSnS₄	I4	This study
Idaite	Cu₂⁺Cu²⁺FeS₄	Unknown	Frenzel (1959)

Acknowledgements

We gratefully acknowledge the support of the Arizona Science Foundation and CNPq 202469/2011–5 from the Brazilian Government for MBA. Special thanks go to Dr David Brown for pointing out that bond-valence calculations corroborate the ordering of Cu to the Ag2 site.

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