Photon Factory Activity Report 2018 #36 (2019)

P-V-T equation of state of -CrOOH

AR-NE5C/2018G023

Chikara SHITO1,*, Keitaro OKAMOTO1, Yuki SATO1, Ryuji WATANABE1, Tomonori OHASHI1,Kazuhiro FUCHIZAKI2, Takahiro KURIBAYASHI1 and Akio SUZUKI1
1Tohoku University, Sendai, 980-8578, Japan
2
Ehime University, Matsuyama 790-8577, Japan
1 Introduction
Distorted rutile-type MOOH is characterized by OH⸱⸱⸱O hydrogen bonds in a–b plane and an edge-sharing
MO6 octahedral chain along the c-axis (Fig. 1). In AlOOH, with distorted rutile-type structure, pressureinduced hydrogen bond symmetrization occurs due to theshortening of the O-H⸱⸱⸱O bond [1].

increases. At the higher temperature, the O-H⸱⸱⸱O distance
may be the longer because of thermal expansion. Thus, thisresult implies that hydrogen bond symmetrization of
distorted rutile-type MOOH can be dominated by the OH⸱⸱⸱O distance. In the Earth’s interior, hydrogen bondsymmetrization could occur at above the pressure
estimated under ambient temperature conditions. However,
we do not know whether such temperature effects areuniversal with regard to distorted rutile-type MOOH.
Further studies on distorted rutile-type MOOH at highpressures and high temperatures are required.

Fig. 1: Structures of distorted rutile-type MOOH. (a) Hasymmetric model (P21nm), (b) H-disorder model (Pnnm),(c) H-centered model (Pnnm).
Anisotropic stiffening behaviors, i.e., changes incompression behaviors related to hydrogen bondsymmetrization, have been observed [1,2,3]. The stiffening
behaviors result in an increase in the bulk modulus and adecrease in a- or b-axis compressibility because of theformation of strong hydrogen bonds in the a–b plane.
Elastic parameters of -CrOOH were determined by using
X-ray diffraction in DAC [3]. However, P-V-T relationshipof -CrOOH has not yet been revealed.
2 Experiment
In situ X-ray diffraction experiments were performed at
the beamline AR-NE5C of the Photon Factory, KEK. A
cubic-type multi-anvil apparatus, MAX80, was used in theexperiments. An MA 6-6 type cell assembly [4], which has
six second-stage WC anvils, was used. The energydispersive method was adopted, and the diffracted X-rays
were collected using a Ge-SSD set at 2 = 6°. The X-ray
diffraction experiments were conducted at pressures of upto 6.2 GPa and temperatures of up to 700 K.
3 Results and Discussion
P-V-T data were fitted to the second-order BirchMurnaghan equation of state (Fig. 2). Thermoelastic
parameters of -CrOOH were determined as follows: bulk
modulus KT0 = 191(4) GPa, temperature derivative(∂K/∂T)P = −0.04(2) GPa K-1, and volumetric thermal
expansion coefficient  = 3.3(2) × 10-5 K-1. The thermoelastic parameters have similar values to those of FeOOH [5] and RhOOH [6].
Fig. 3 indicates that the pressure of the changes in thecompression behaviors tends to increase as the temperature

Fig. 2: P-V plot with isothermal compression curves.

Fig. 3: Pressure evolution of axial ratio of -CrOOH.
References[1] A. Sano-Furukawa et al., Sci. Rep. 8, 15520 (2018).
[2] T. Kuribayashi et al., Phys. Chem. Minerals 41, 303–312 (2014).
[3] A. Sano-Furukawa et al., Phys. Chem. Minerals 39,375–383 (2012).
[4] N. Nishiyama et al., High Pres. Res. 28, 307–314(2008).
[5] A. Suzuki, J. Mineral. Petrol. Sci. 111, 420–424 (2016).
[6] A.Suzuki, High Pres. Res. 38, 145–152 (2018).
* chikara.shito.r4@dc.tohoku.ac.jp