Structures and phase transitions of trigonal ZrMo₂O₈ and HfMo₂O₈

This paper describes the structures, thermal-expansion properties and phase transitions of the trigonal forms of ZrMo₂O₈ and HfMo₂O₈. Both phases adopt a structure at room temperature and show positive thermal expansion. Both phases also undergo a displacive phase transition at high temperature (ZrMo₂O₈ at 487 K and HfMo₂O₈ at 463 K) to a higher-symmetry structure that has lower thermal expansion. The structure of the high-temperature α′-AMo₂O₈ form (A = Zr and Hf) has been refined from powder diffraction data in space group Pm1.

Computing details

Figures

(alpha_zrmo2o8)

Crystal data

?	β = 90°
Mr = ?	γ = 120°
?, ?	V = 1041.58 (7) Å^3
a = 10.1367 (3) Å	Z = ?
b = 10.1367 (3) Å	? radiation, λ = ? Å
c = 11.7050 (3) 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
Zr1	0	0	0	0.80 (9)
Zr2	0.333333	0.666667	0.98380 (11)	1.11 (5)
Mo1	0.32797 (18)	0.33766 (17)	0.15668 (4)	0.83 (2)
O1	0.3442 (3)	0.49829 (19)	0.08105 (8)	1.89 (4)
O2	0.50662 (17)	0.3333 (3)	0.11810 (10)	1.38 (3)
O3	0.1785 (2)	0.1650 (2)	0.10359 (13)	1.60 (5)
O4	0.33020 (16)	0.35219 (13)	0.29202 (5)	1.81 (3)

(alpha_hfmo2o8)

Crystal data

?	β = 90°
Mr = ?	γ = 120°
?, ?	V = 1037.33 (6) Å^3
a = 10.1043 (3) Å	Z = ?
b = 10.1043 (3) Å	? radiation, λ = ? Å
c = 11.7320 (3) 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
Hf1	0	0	0	0.49 (8)
Hf2	0.333333	0.666667	0.98341 (9)	0.38 (4)
Mo1	0.33844 (19)	0.33762 (18)	0.14804 (4)	0.77 (3)
O1	0.3442 (3)	0.5003 (2)	0.08080 (9)	1.82 (4)
O2	0.50901 (18)	0.3339 (3)	0.11666 (10)	1.52 (4)
O3	0.1677 (2)	0.1637 (2)	0.10290 (14)	1.49 (5)
O4	0.32086 (19)	0.35254 (16)	0.29140 (5)	2.05 (3)

(alphaprimezrmo2o8)

Crystal data

?	β = 90°
Mr = ?	γ = 120°
?, ?	V = 177.41 (2) Å^3
a = 5.8460 (3) Å	Z = ?
b = 5.8460 (3) Å	? radiation, λ = ? Å
c = 5.9941 (3) 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
Zr1	0	0	0	0
Mo1	0.333333	0.666667	0.29183 (9)	0
O1	0.16614 (7)	0.83386 (7)	0.19598 (12)	0
O4	0.333333	0.666667	0.57172 (14)	0