# In situ high-pressure synchrotron X-ray powder diffraction study of tunnel manganese oxide minerals: hollandite, romanechite, and todorokite

Gil Chan Hwang, Jeffrey E. Post, Yongjae Lee

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2 Citations (Scopus)

## Abstract

In situ high-pressure synchrotron X-ray powder diffraction study of three tunnel manganese oxide minerals (hollandite with 2 × 2 MnO6octahedra tunnels, romanechite with 2 × 3 tunnels, and todorokite with 3 × 3 tunnels) was performed using a diamond anvil cell and nominally penetrating alcohol and water mixture as a pressure-transmitting medium up to ~8 GPa. Bulk moduli (B0)calculated using Murnaghan’s equation of state are inversely proportional to the size of the tunnel, i.e., 134(4) GPa for hollandite (I2/m), 108(2) GPa for romanechite (C2/m), and 67(5) GPa for todorokite (P2/m). On the other hand, axial compressibilities show different elastic anisotropies depending on the size of the tunnel, i.e., $$\beta_{0}^{a}$$β0a(a/a0)=−0.00066(3) GPa−1, $$\beta_{0}^{b}$$β0b (b/b0)=0.00179(8) GPa−1,$$\beta_{0}^{c}$$β0c(c/c0)=0.00637(4) GPa−1[c > b > a]for hollandite;$$\beta_{0}^{a}$$β0a(a/a0)=0.00485(4) GPa−1,$$\beta_{0}^{b}$$β0b (b/b0)=0.0016(1) GPa−1, $$\beta_{0}^{c}$$β0c(c/c0)=0.00199(8) GPa−1[a > c > b] for romanechite; and $$\beta_{0}^{a}$$β0a(a/a0)=0.00826(9)GPa−1,$$\beta_{0}^{b}$$β0b(b/b0)=0.0054(1)GPa−1, $$\beta_{0}^{c}$$β0c(c/c0)=0.00081(8) GPa−1[a > b > c] for todorokite.Overall, the degree of tunnel distortion increases with increasing pressure and correlates with the size of the tunnel, which is evidenced by the gradual increases in the monoclinic β angles up to 3 GPa of 0.62°,0.8°, and 1.15° in hollandite, romanechite, and todorokite, respectively. The compression of tunnel manganese oxides is related to the tunnel distortion and the size of the tunnel.

Original language English 405-411 7 Physics and Chemistry of Minerals 42 5 https://doi.org/10.1007/s00269-014-0731-8 Published - 2015 May 1

### Bibliographical note

Funding Information:
This work was supported by the Global Research Laboratory Program of the Korean Ministry of Science, ICT and Planning (MSIP). Experiments using synchrotron were supported by Pohang Accelerator Laboratory in Korea through the abroad beamtime program of Synchrotron Radiation Facility Project under the MSIP and have been performed under the approval of the NSLS. Research carried out in part at the NSLS at BNL is supported by the U.S. Department of Energy, Office of Basic Energy Sciences. GCH thanks the support from the Yonsei University Research Fund of 2014-12-0140. JEP acknowledges funding by NSF grants EAR07-45374 and EAR11-47728.