Synchrotron study of the garnet-type oxide Li(6)CaSm(2)Ta(2)O(12).

Hexalithium calcium disamarium(III) ditantalum(V) dodeca-oxide, Li(6)CaSm(2)Ta(2)O(12), crystallizes in a cubic garnet-type structure. In the crystal structure, disordered Li atoms occupy two crystallographic sites. One Li has a tetra-hedral coordination environment in the oxide lattice, whereas the other Li atom occupies a significantly distorted octa-hedral site, with site occupancies for the two Li atoms of 0.26 (7) and 0.44 (2), respectively. Ca and Sm atoms are statistically distributed over the same crystallographic position with a occupancy of 2/3 for Sm and of 1/3 for Ca, and are eightfold coordinated by O atoms. The TaO(6) octa-hedron is joined to six others via corner-sharing LiO(4) tetra-hedra. One Li and the O atoms lie on general positions, while the other atoms are situated on special positions. The Sm/Ca position has 222, Ta has , and the tetra-hedrally coordinated Li atom has site symmetry.

Related literature

For a general description of structures and physical properties of garnets, see: Geller (1967 ▶). Recently, high Li-ion conductivity was discovered in garnet-related compounds such as Li5La3 M 2O12 (M = Nb, Ta), see: Thangadurai et al. (2003 ▶); Cussen (2006 ▶). For studies focused on the substitution of La3+ by divalent alkaline earth ions (Ca, Sr, Ba), see: Murugan et al. (2007 ▶); Thangadurai & Weppner (2005a ▶,b ▶); O’Callaghan & Cussen (2007 ▶); Percival & Slater (2007 ▶). For indexing the powder diffraction pattern, see: Boultif & Louër (2004 ▶).

Experimental

Crystal data

Li6CaSm2Ta2O12

M = 936.45

Cubic,

a = 12.55128 (7) Å

V = 1977.26 (2) Å3

Z = 8

Synchrotron radiation

λ = 1.54900 Å

T = 298 K

Specimen shape: flat sheet

20 × 20 × 0.5 mm

Specimen prepared at 103 kPa

Specimen prepared at 1223 K

Particle morphology: particle, yellowish-white

Data collection

Pohang Light Source 8C2 HRPD Beamline diffractometer

Specimen mounting: ’packed powder pellet’

Specimen mounted in reflection mode

Scan method: step

2θmin = 10.0, 2θmax = 131.0°

Increment in 2θ = 0.01°

Refinement

R p = 15.0

R wp = 22.0

R exp = 13.1

R B = 6.62

S = 1.67

Excluded region(s): None

Profile function: pseudo Voigt

151 reflections

20 parameters

Preferred orientation correction: none

Data collection: local software at 8C2 HRPD beamline; cell refinement: FULLPROF (Rodriguez-Carvajal, 2001 ▶); data reduction: FULLPROF; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: FULLPROF; molecular graphics: DIAMOND (Brandenburg, 1999 ▶); software used to prepare material for publication: FULLPROF.

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809040008/wm2261sup1.cif

Rietveld powder data: contains datablocks I. DOI: 10.1107/S1600536809040008/wm2261Isup2.rtv

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

Li6CaSm2Ta2O12	Dx = 6.292 Mg m−3
Mr = 936.45	Synchrotron radiation, λ = 1.5490 Å
Cubic, Ia3d	T = 298 K
Hall symbol: -I 4bd 2c 3	Particle morphology: particle
a = 12.55128 (7) Å	yellowish-white
V = 1977.26 (2) Å3	flat sheet, 20 × 20 mm
Z = 8	Specimen preparation: Prepared at 1223 K and 103 kPa, cooled at 5 K/min K min−1
F(000) = 3200

Pohang Light Source 8C2 HRPD Beamline diffractometer	Data collection mode: reflection
Radiation source: Synchrotron	Scan method: step
Si 111	2θmin = 10.00°, 2θmax = 131.00°, 2θstep = 0.01°
Specimen mounting: 'packed powder pellet'

Rp = 15.0	Profile function: pseudo Voigt
Rwp = 22.0	20 parameters
Rexp = 13.1	0 restraints
RBragg = 6.62	(Δ/σ)max < 0.001
χ2 = 2.789	Background function: manual background
12100 data points	Preferred orientation correction: 'None'
Excluded region(s): None

	x	y	z	Uiso*/Ueq	Occ. (<1)
Sm1	0.00000	0.25000	0.62500	0.0089 (2)*	0.6666
Ca1	0.00000	0.25000	0.62500	0.0089 (2)*	0.3333
Ta1	0.00000	0.00000	0.50000	0.0071 (2)*
Li1	0.12500	0.00000	0.75000	0.0278 (11)*	0.26 (7)
Li2	0.101 (5)	0.192 (5)	0.412 (5)	0.0278 (11)*	0.44 (2)
O1	0.0323 (5)	0.0521 (5)	0.6488 (6)	0.0079 (13)*

(Sm,Ca)—O1i	2.441 (18)	Li1—O1xiv	1.843 (7)
(Sm,Ca)—O1ii	2.441 (18)	Li2—O1xv	1.63 (6)
(Sm,Ca)—O1iii	2.441 (18)	Li2—O1xi	2.14 (6)
(Sm,Ca)—O1iv	2.441 (18)	Li2—O1i	2.12 (6)
(Sm,Ca)—O1v	2.561 (17)	Li2—O1iii	2.20 (6)
(Sm,Ca)—O1	2.561 (17)	Li2—O1xvi	2.55 (6)
(Sm,Ca)—O1vi	2.561 (17)	Li2—O1vii	2.69 (6)
(Sm,Ca)—O1vii	2.561 (17)	Li1—Li2viii	1.53 (6)
Ta1—O1viii	2.014 (6)	Li1—Li2xvii	1.53 (6)
Ta1—O1	2.014 (6)	Li1—Li2xviii	1.53 (6)
Ta1—O1ix	2.014 (6)	Li1—Li2xix	1.53 (6)
Ta1—O1x	2.014 (6)	Li1—Li2xx	2.33 (6)
Ta1—O1xi	2.014 (6)	Li1—Li2ix	2.33 (6)
Ta1—O1i	2.014 (6)	Li1—Li2vii	2.33 (6)
Li1—O1xii	1.843 (7)	Li1—Li2xxi	2.33 (6)
Li1—O1	1.843 (7)	Li2—Li2xxii	2.27 (9)
Li1—O1xiii	1.843 (7)	Li2—Li2xxiii	2.27 (9)
O1i—(Sm,Ca)—O1ii	158.8 (8)	O1—Ta1—O1x	180.000 (1)
O1i—(Sm,Ca)—O1iii	72.8 (2)	O1ix—Ta1—O1x	87.2 (3)
O1ii—(Sm,Ca)—O1iii	111.2 (2)	O1viii—Ta1—O1xi	180.0 (4)
O1i—(Sm,Ca)—O1iv	111.2 (2)	O1—Ta1—O1xi	92.8 (3)
O1ii—(Sm,Ca)—O1iv	72.8 (2)	O1ix—Ta1—O1xi	87.2 (3)
O1iii—(Sm,Ca)—O1iv	158.8 (8)	O1x—Ta1—O1xi	87.2 (3)
O1i—(Sm,Ca)—O1v	74.0 (2)	O1viii—Ta1—O1i	87.2 (3)
O1ii—(Sm,Ca)—O1v	124.5 (4)	O1—Ta1—O1i	87.2 (3)
O1iii—(Sm,Ca)—O1v	95.4 (2)	O1ix—Ta1—O1i	180.000 (2)
O1iv—(Sm,Ca)—O1v	67.2 (2)	O1x—Ta1—O1i	92.8 (3)
O1i—(Sm,Ca)—O1	67.9 (8)	O1xi—Ta1—O1i	92.8 (3)
O1ii—(Sm,Ca)—O1	95.4 (2)	O1xii—Li1—O1	113.7 (6)
O1iii—(Sm,Ca)—O1	124.5 (4)	O1xii—Li1—O1xiii	101.7 (3)
O1iv—(Sm,Ca)—O1	74.0 (2)	O1—Li1—O1xiii	113.7 (6)
O1v—(Sm,Ca)—O1	108.13 (16)	O1xii—Li1—O1xiv	113.7 (6)
O1i—(Sm,Ca)—O1vi	124.5 (4)	O1—Li1—O1xiv	101.7 (3)
O1ii—(Sm,Ca)—O1vi	74.0 (2)	O1xiii—Li1—O1xiv	113.7 (6)
O1iii—(Sm,Ca)—O1vi	67.2 (2)	O1xv—Li2—O1i	110 (3)
O1iv—(Sm,Ca)—O1vi	95.4 (2)	O1xi—Li2—O1i	87 (2)
O1v—(Sm,Ca)—O1vi	73.41 (16)	O1xv—Li2—O1iii	106 (3)
O1—(Sm,Ca)—O1vi	167.0 (2)	O1xi—Li2—O1iii	150 (10)
O1i—(Sm,Ca)—O1vii	95.4 (2)	O1i—Li2—O1iii	83 (2)
O1ii—(Sm,Ca)—O1vii	67.2 (2)	O1xv—Li2—O1xvi	87 (10)
O1iii—(Sm,Ca)—O1vii	74.0 (2)	O1xi—Li2—O1xvi	82 (2)
O1iv—(Sm,Ca)—O1vii	124.5 (4)	O1i—Li2—O1xvi	165 (10)
O1v—(Sm,Ca)—O1vii	167.0 (2)	O1iii—Li2—O1xvi	101 (2)
O1—(Sm,Ca)—O1vii	73.41 (16)	O1xv—Li2—O1vii	148 (10)
O1vi—(Sm,Ca)—O1vii	108.13 (16)	O1xi—Li2—O1vii	78.4 (19)
O1viii—Ta1—O1	87.2 (3)	O1i—Li2—O1vii	98 (10)
O1viii—Ta1—O1ix	92.8 (3)	O1iii—Li2—O1vii	74.8 (18)
O1—Ta1—O1ix	92.8 (3)	O1xvi—Li2—O1vii	67 (6)
O1viii—Ta1—O1x	92.8 (3)

Table 1

Selected bond lengths (Å)

(Sm,Ca)—O1	2.561 (17)
Ta1—O1	2.014 (6)
Li1—O1	1.843 (7)
Li2—O1i	1.63 (6)
Li2—O1ii	2.14 (6)
Li2—O1iii	2.12 (6)
Li2—O1iv	2.20 (6)
Li2—O1v	2.55 (6)
Li2—O1vi	2.69 (6)

Symmetry codes: (i) ; (ii) ; (iii) ; (iv) ; (v) ; (vi) .