Volume 122, Number 6, June 2018
|Number of page(s)||6|
|Section||Condensed Matter: Structural, Mechanical and Thermal Properties|
|Published online||26 July 2018|
Structural properties of β-metal(II) hydroxides: Combined XAS and Raman spectroscopic studies on lattice stability
1 ALBA Synchrotron, Cerdanyola del Vallès - 08290 Barcelona, Spain
2 Elettra-Sincrotrone Trieste - S.S. 14- km 163,5, 34149 Basovizza, Trieste, Italy
3 Dipartimento di Fisica, Università di Roma “Sapienza” - Piazzale Aldo Moro 2, 00185 Roma, Italy
Received: 4 April 2018
Accepted: 29 June 2018
Temperature-dependent x-ray absorption (XAS) and high-pressure (HP) Raman spectroscopy results on two prominent β-metal(II) hydroxides, viz. β-Ni(OH)2 and β-Co(OH)2 are presented. Raman data at ambient conditions show the β-Co(OH)2 phonons to be softer than the β-Ni(OH)2 ones. Analysis of the extended x-ray absorption fine structure data at metal K-edge as a function of temperature reveals the Einstein frequencies of the metal-oxygen and the metal-metal bonds to be, respectively, 309 and for β-Co(OH)2 and the same to be 385 and for β-Ni(OH)2. In both the β-metal(II) hydroxides, up to about 10 GPa, HP Raman spectroscopy show a continuous hardening of the phonon modes associated with the metal-oxygen sub-lattices, whereas a systematic frequency softening is displayed by the hydroxyl symmetric stretching mode. These contrasting behaviours imply a gradual development of lattice instability with pressure mainly due to the displacement of H atoms around the metal-oxygen axis. The presented data allow a direct comparison of the local-lattice behaviour by quantifying the strength (XAS) and anharmonicity (RAMAN) of the atomic bonds in the two systems.
PACS: 61.05.cj – X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc. / 65.40.-b – Thermal properties of crystalline solids / 78.30.Er – Solid metals and alloys
© EPLA, 2018
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