Displacive phase-transition of cuprite Ag2O revealed by extended x-ray absorption fine structure

Effect of dynamic high-pressure loading on decomposition reaction and negative thermal expansion of silver oxide

“…If the Bragg peak at 2θ = 21.5°can be assigned to the (10-10) plane of hexagonal Ag 2 O, then the hexagonal Ag 2 O showed a positive thermal expansion because the Bragg peak position moved to a higher angle during cooling. Similar behavior was recognized for the Bragg peaks at 2θ = 24.7°, 37.8°and 44.9°, which were assigned to the (01-11), (11)(12)(13)(14)(15)(16)(17)(18)(19)(20), and (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) planes of hexagonal phase Ag 2 O. All of the synchrotron powder XRD patterns for the unshocked and shocked samples are shown in Fig.…”

“…One of the interesting properties of Ag 2 O is its negative thermal expansion behavior. [12][13][14][15][16][17] In addition to the exploration of traces of shock-induced phase transition and to reveal the effect of shock compression on the negative thermal expansion behavior, synchrotron powder XRD measurements were performed from 300 to 130 K. Figure 6 shows synchrotron powder XRD patterns for the unshocked and shocked samples. The synchrotron powder XRD patterns for the unshocked sample and the sample shocked at 3.5 GPa revealed the presence of AgO in addition to phase I of Ag 2 O and metallic Ag.…”

“…13,14) Extended Xray absorption fine structure (EXAFS) spectroscopy and diffraction analysis revealed a connection with strong perpendicular vibrations of Ag atoms, which ruled out the possibility of explaining the negative thermal expansion by a simple rigid unit mode model. 13,17) Previous EXAFS spectroscopy results indicated that there are two types of Ag-Ag distance with different signed thermal expansion coefficients and a positive expansion of Ag-O bonding. 12,13,17) Although no definitive conclusions can be drawn on the basis of the present results, it is speculated that shock-induced defects and strain, and defects caused by the shock-induced decomposition of Ag 2 O and AgO, and those caused by shock-induced phase transition disturbed the vibrations between atoms and contributed to the suppression of the negative thermal expansion.…”

“…One of the interesting properties of Ag 2 O is its negative thermal expansion behavior. [12][13][14][15][16][17] Ag 2 O has a negative thermal expansion up to its decomposition temperature at about 450 K. 14,15) Negative thermal expansion behavior can be affected by local structures of Ag 2 O and those are modified by shock compression.…”