Structures and the oxygen deficiency of tetragonal and monoclinic zirconium oxide nanoparticles

The crystal structure of zirconium oxide nanoparticles was refined by the Rietveld analysis of synchrotron X-ray powder diffraction data measured at 298 K. In the nanoparticles, two phases of tetragonal ZrO_2 − δ (average particle size: 11 ± 2 nm) and monoclinic ZrO₂ (average particle size: 24 ± 4 nm) existed, where the weight fractions were estimated to be 84.9 and 15.1 wt%, respectively. The structural refinement suggests that the tetragonal ZrO_2 − δ has an oxygen deficiency [δ = 0.031 (7)] and that the monoclinic ZrO_2 − δ has less oxygen deficiency (δ ≃ 0), where δ is the vacancy concentration. The monoclinic ZrO₂ has a larger unit-cell volume. The maximum-entropy method analysis indicated covalent bonding between Zr and O atoms.

S1. Experimental

Precursor sols were prepared from a mixture of 70 wt% zirconium (IV) propoxide 1-propanol solution and 98 wt% triethanolamine. The sols were hydrolyzed with half volume of water in a Teflon-lined autoclave at 110 oC for 24 h and then at 120 oC for 120 h. A white fine powder was separated from the mother solution by a centrifuge and rinsed several times with ethanol. In order to obtain zirconium oxide nanocrystallites, the ethanol sol was dried in air on a quartz plate at 125 oC for 22 h(Tsunekawa et al., 2005b).

S2. Refinement

The crystal structure of the zirconium oxide nanocrystallites was refined by the Rietveld method with a computer program RIETAN-2000 (Izumi & Ikeda, 2000).

Computing details

Data collection: RIGAKU software (Toraya et al., 1996) for (I). Cell refinement: RIETAN-2000 (Izumi and Ikeda, 2000) for (I). Program(s) used to solve structure: RIETAN-2000 for (I). Program(s) used to refine structure: RIETAN-2000 for (I). Molecular graphics: VENUS [Izumi and Dilanian (2002)] for (I).

Figures

Fig. 1. Rietveld refinement of the synchrotron X-ray powder diffraction data of the zirconium oxide nanoparticles. Magnified view of the peak profile in the 2 range from 80 to 140 °. is inserted. Red points and green line denote the observed and calculated intensities, respectively. The difference between the observed and calculated intensities is drawn by a blue line below the profile. Up and down green short verticals denote the calculated peak positions of the monoclinic and tetragonal phases, respectively.

Fig. 2. (A) Refined crystal structure and equi-electron-density surfaces (B) at 10 and (C) at 1 ?-3 of the tetragonal zirconium oxide nanoparticles. Two bond lengths between the cation and anion are R = 2.3562 (6) ? and r = 2.0805 (5) ?. Arrows stand for the displacements of oxygen atoms along the c axis (0.237 (1) ?).

(I) zirconium oxide

Crystal data

O^2^−xZr	Dx = 6.159 Mg m^−3
Mr = 246.49	Monochromatized synchrotron X-ray 1.20200 radiation, λ = 1.20200 Å
Tetragonal, P42/nmc	T = 298 K
a = 3.58651 (8) Å	Particle morphology: plate-like
c = 5.16658 (15) Å	white
V = 66.46 (1) Å^3	flat sheet, 12 × 12 mm
Z = 2	Specimen preparation: Prepared at 398 K
F(000) = 111.192

Data collection

A multiple-detector system with Ge(111) analyzer crystals, Soller slits and scintillation counters (Toraya et al., 1996) diffractometer	Data collection mode: reflection
Radiation source: synchrotron X-ray	Scan method: step
Ge(111) analyzer crystals monochromator	2θmin = 10.501°, 2θmax = 154.808°, 2θstep = 0.01°
Specimen mounting: packed powder pellet

Refinement

Rp = 0.047	Profile function: a split-type Pearson VII (Toraya, 1990)
Rwp = 0.061	57 (13 for structural parameters) parameters
Rexp = 0.063
RBragg = 0.009	Background function: twelve-parameter polynomial in 2theta^n, where n has values between 0 and 11
χ^2 = 1.690	Preferred orientation correction: no
14432 data points

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Zr0.994Hf0.006	0	0	0	0.385 (1)*
O	0	0.5	0.2042 (2)	0.934 (17)*	0.984 (4)

Bond lengths (Å)

M—O

2.3562 (6)

M—O

2.0805 (5)

(VICS_phase_1)

Crystal data

?	β = 90°
Mr = ?	γ = 90°
?, P42/nmc	V = ? Å^3
a = 3.58651 (8) Å	Z = ?
b = 3.58651 (8) Å	? radiation, λ = ? Å
c = 5.16658 (8) Å	× × mm
α = 90°

Data collection

h = ?→?	l = ?→?
k = ?→?

Refinement

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

	x	y	z	Biso*/Beq	Occ. (<1)
Zr	0	0	0	0.385 (1)*
O	0	0.50000	0.2041 (3)	0.934 (17)*	0.984 (4)