Structural analysis of excess-anion C-type rare earth oxide: a case study with Gd_1-xCe_xO_1.5+x/2 (x = 0.20 and 0.40)

Structural analysis of anion-rich C-type Gd₂O₃ was carried by the Rietveld refinement of the powder X-ray diffraction data for compositions Gd_0.8Ce_0.2O_1.60 and Gd_0.6Ce_0.4O_1.70. Both compounds have a body-centred cubic lattice (space group Ia, No. 206, Z = 32) with unit-cell parameters of 10.8488 (1) and 10.8542 (1) Å, respectively. Both of these compounds are iso-structural with the C-type rare earth oxides, with excess anions as required for charge balance. The structural analysis reveals that there are two different kinds of metal ion site, namely 8b (M1) and 24d (M2), and two different kinds of anion sites, namely 48e (O1) and 16c (O2). The excess anions occupy the 16c (xxx) sites. The two metal ions each form an approximately eightfold-coordination polyhedron with O1 and O2. The details of these two compositions are explained and compared with both the CeO₂ structure and the Gd₂O₃ structure, i.e. the end member.

Computing details

For both compounds, program(s) used to refine structure: FULLPROF.

Figures

(I) Gadolinium Cerium oxide

Crystal data

Gd0.6Ce0.4O1.70	Dx = 7.38 Mg m^−3
Mr = 177.60	X-ray radiation, λ = ? Å
Cubic, IA3	T = 293 K
Hall symbol: -I 2b 2c 3	White
a = 10.8542 (1) Å	flat sheet, ? × ? × ? mm
V = 1278.76 (1) Å^3	Specimen preparation: Prepared at 1673K K, cooled at 2K/min K min^−1
Z = 32

Data collection

Philips PW1710 diffractometer	Data collection mode: reflection
Radiation source: sealed X-ray tube	Scan method: Step
Graphite 002 face monochromator	2θmin = 10.000°, 2θmax = 110.000°, 2θstep = 0.020°
Specimen mounting: Sample pasted with on glass slide with collodion binder

Refinement

Rp = 8.30	Profile function: 'Pseudo-voigt function' 'U = 0.01502(471) V = -0.00722(529) W = 0.01885(145)' 'Eta = 0.633(35), X = 0.0069(8)'
Rwp = 11.4	1 parameters
Rexp = 9.25	0 restraints
RBragg = 4.79
χ^2 = NOT FOUND	Background function: 5th order polynomial function
5001 data points	Preferred orientation correction: 'March function' axis (001), G1 = 0.9608(57),

Special details

Experimental. Samples were prepared by solid state reaction of appropriate amounts of Gd2O3 and CeO2 at 1573 K followed by 1673 K for 48 hrs. Heating and cooling rates are 2 degrees per min. Details are given in manuscript

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Gd1	0.25000	0.25000	0.25000	0.02984*	0.6
Ce1	0.25000	0.25000	0.25000	0.02984*	0.4
Gd2	−0.0188 (2)	0.00000	0.25000	0.01591*	0.6
Ce2	−0.0188 (2)	0.00000	0.25000	0.01591*	0.4
O1	0.3880 (17)	0.1391 (16)	0.376 (3)	0.01635*	0.95 (4)
O2	0.402 (2)	0.402 (2)	0.402 (2)	0.01635*	0.56 (4)

(II) Gadolinium Cerium oxide

Crystal data

Gd0.8Ce0.2O1.60	Dx = 7.46 Mg m^−3
Mr = 179.40	X-ray radiation, λ = 1.540600 Å
Cubic, IA3	T = 293 K
Hall symbol: -I 2b 2c 3	White
a = 10.8488 (1) Å	flat sheet, ? × ? × ? mm
V = 1276.86 (2) Å^3	Specimen preparation: Prepared at 1673K K, cooled at 2K/min K min^−1
Z = 32

Data collection

Philips PW1710 diffractometer	Data collection mode: reflection
Radiation source: sealed X-ray tube	Scan method: Step
Graphite 002 face monochromator	2θmin = 10.000°, 2θmax = 110.000°, 2θstep = 0.020°
Specimen mounting: Sample pasted with on glass slide with collodion binder'

Refinement

Rp = 8.48	Profile function: 'Pseudo-voigt function' 'U = 0.04722(448) , V = -0.04828(503), W = 0.02867(138)' 'Eta = 0.525(32), X = 0.0051(7)'
Rwp = 11.5	23 parameters
Rexp = 9.63	0 restraints
RBragg = 5.85
χ^2 = NOT FOUND	Background function: 5th order polynomial function
5001 data points	Preferred orientation correction: 'March function' axis (001), G1 = 1.0088(61),

Special details

Experimental. Samples were prepared by solid state reaction of appropriate amounts of Gd2O3 and CeO2 at 1573 K followed by 1673 K for 48 hrs. Heating and cooling rates are 2 degrees per min. Details are given in manuscript

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Gd1	0.25000	0.25000	0.25000	0.00798*	0.8
Gd1	0.25000	0.25000	0.25000	0.00798*	0.2
Gd2	−0.02515 (14)	0.00000	0.25000	0.00391*	0.8
Gd2	−0.02515 (14)	0.00000	0.25000	0.00391*	0.2
O1	0.3911 (15)	0.1470 (14)	0.3763 (19)	0.00636*	0.96 (6)
O2	0.407 (3)	0.407 (3)	0.407 (3)	0.00636*	0.37 (6)