Sr-fresnoite determined from synchrotron X-ray powder diffraction data.

The fresnoite-type compound Sr2TiO(Si2O7), distrontium oxidotitanium disilicate, has been prepared by high-temperature solid-state synthesis. The results of a Rietveld refinement study, based on high-resolution synchrotron X-ray powder diffraction data, show that the title compound crystallizes in the space group P4bm and adopts the structure of other fresnoite-type mineral samples with general formula A2 TiO(Si2O7) (A = alkaline earth metal cation). The structure consists of titanosilicate layers composed of corner-sharing SiO4 tetra-hedra (forming Si2O7 disilicate units) and TiO5 square-based pyramids. These layers extend parallel to the ab plane and are stacked along the c axis. Layers of distorted SrO6 octa-hedra lie between the titanosilicate layers. The Sr(2+) ion, the SiO4 tetra-hedron and the bridging O atom of the disilicate unit are located on mirror planes whereas the TiO5 square-based pyramid is located on a fourfold rotation axis.

Related literature

For the crystal chemistry of fresnoites, see: Barbar & Roy (2012 ▶); Höche et al. (2002 ▶); ICDD (1989 ▶). For properties of Sr–fresnoites, see: Park & Navrotsky (2010 ▶). Atomic coordinates as starting parameters for the Rietveld refinement (Rietveld, 1969 ▶) of the present phases were taken from Ochi (2006 ▶); Goldschmidt & Thomassen (1923 ▶); Machida et al. (1982 ▶); Mitchell et al. (2000 ▶). For related strontium titanosilicates, see: Miyajima et al. (2002 ▶). For synchrotron data analysis, see: Hammersley (1997 ▶); Hammersley et al. (1996 ▶).

Experimental

Crystal data

Sr2TiSi2O8

M = 407.31

Tetragonal,

a = 8.3200 (3) Å

c = 5.0239 (2) Å

V = 347.77 (2) Å3

Z = 2

Synchrotron radiation, λ = 0.207549 Å

μ = 0.43 mm−1

T = 293 K

Cylinder, 20 × 0.7 mm

Data collection

In-house design diffractometer

Specimen mounting: capillary

Data collection mode: transmission

Scan method: continuous

2θmin = 0.053°, 2θmax = 11.915°, 2θstep = 0.008°

Refinement

R p = 0.052

R wp = 0.073

R exp = 0.031

R Bragg = 0.093

χ2 = 31.068

1476 data points

71 parameters

5 restraints

Data collection: local software; cell refinement: local software; data reduction: local software; program(s) used to solve structure: coordinates taken from a related compound; program(s) used to refine structure: FULLPROF (Rodriguez-Carvajal, 2001 ▶); molecular graphics: VESTA (Momma & Izumi, 2008 ▶); software used to prepare material for publication: publCIF (Westrip, 2010 ▶).

Click here for additional data file.

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S1600536812048921/wm2699sup1.cif

Click here for additional data file.

Rietveld powder data: contains datablock(s) I. DOI: 10.1107/S1600536812048921/wm2699Isup2.rtv

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Sr2TiSi2O8	Dx = 3.890 (1) Mg m−3
Mr = 407.31	Synchrotron radiation, λ = 0.207549 Å
Tetragonal, P4bm	µ = 0.43 mm−1
Hall symbol: P 4 -2ab	T = 293 K
a = 8.3200 (3) Å	Particle morphology: powder
c = 5.0239 (2) Å	white
V = 347.77 (2) Å3	cylinder, 20 × 0.7 mm
Z = 2	Specimen preparation: Prepared at 1323 K and 100 kPa

In-house design diffractometer	Data collection mode: transmission
Radiation source: Synchrotron	Scan method: continuous
Laue DCM diamond(111) & Si(111) monochromator	2θmin = 0.053°, 2θmax = 11.915°, 2θstep = 0.008°
Specimen mounting: capillary

Rp = 0.052	Excluded region(s): 0-1 and 11.7-12.0 degrees 2θ
Rwp = 0.073	Profile function: T-C-H Pseudo-Voigt function
Rexp = 0.031	71 parameters
RBragg = 0.093	5 restraints
χ2 = 31.068
1476 data points

	x	y	z	Uiso*/Ueq
Sr1	0.3282 (2)	0.8282 (2)	0.017 (2)	0.0070 (8)*
Ti1	0.00000	0.00000	0.558 (3)	0.007 (2)*
Si1	0.1305 (6)	0.6305 (6)	0.535 (3)	0.019 (2)*
O1	0.00000	0.50000	0.651 (5)	0.017 (3)*
O2	0.1292 (15)	0.6292 (15)	0.191 (3)	0.017 (3)*
O3	0.2985 (12)	0.5984 (15)	0.678 (3)	0.017 (3)*
O4	0.00000	0.00000	0.209 (3)	0.017 (3)*

Sr1—O1i	2.733 (18)	Ti1—O3viii	1.961 (12)
Sr1—O2	2.499 (13)	Ti1—O3ix	1.961 (13)
Sr1—O2ii	2.676 (13)	Ti1—O4	1.75 (2)
Sr1—O2iii	2.676 (13)	Si1—O1	1.642 (11)
Sr1—O3iv	2.572 (15)	Si1—O2	1.73 (2)
Sr1—O3v	2.572 (14)	Si1—O3	1.594 (14)
Ti1—O3vi	1.961 (12)	Si1—O3x	1.594 (15)
Ti1—O3vii	1.961 (13)
O3xi—Ti1xii—O3xiii	84.6 (9)	O3x—Ti1xii—O4xii	107.9 (12)
O3xi—Ti1xii—O3xiv	144.2 (10)	O3xiv—Ti1xii—O4xii	107.9 (12)
O3xiv—Ti1xii—O3xiii	84.6 (8)	O1—Si1—O2	110.3 (16)
O3xi—Ti1xii—O4xii	107.9 (12)	O1—Si1—O3x	108.0 (9)
O3xiv—Ti1xii—O3x	84.6 (8)	O1—Si1—O3	108.0 (10)
O3xiii—Ti1xii—O3x	144.2 (11)	O2—Si1—O3	117.1 (15)
O3xiii—Ti1xii—O4xii	107.9 (12)	O2—Si1—O3x	117.1 (15)
O3x—Ti1xii—O3xi	84.6 (9)	O3x—Si1—O3	95.2 (11)