In situ XRPD study of the ambient-pressure synthesis of nonstoichiometric Ag3O from Ag–Ag2O thin films: Phase abundance, unit-cell parameters, and c/a as a function of temperature and time. Issue 4 (December 2020)

• Record Type: Journal Article
• Authors: Schields, Paul J.; Dunwoody, Nicholas; Field, David; Wilson, Zachary
• Is Part Of: Powder diffraction. Volume 35:Issue 4(2020)
• Page Start: 247
• Page End: 261
• Publication Date: 2020-12
• Subjects: Ag3O, -- Ag2O, -- Ag, -- in situ thermal reaction, -- thermal expansion, -- nonstoichiometry, -- XRPD; Powder metallurgy -- Periodicals; Materials -- Analysis -- Periodicals; 620.1127
• DOI: 10.1017/S0885715620000561
• Languages: English
• ISSNs: 0885-7156

Abstract

Abstract : Ag3 O was synthesized by jet-milling magnetron-sputtered Ag–Ag2 O thin films. Heating the jet-milled powders in air and N2 from 40 to 148 °C at ambient pressure produced Ag3 O-rich powders. The phase composition and unit-cell parameters of the jet-milled powders were measured as a function of temperature with in situ X-ray powder diffraction experiments from −186 to 293 °C. Ag3 O was also produced by ball milling and sonicating jet-milled films at ambient conditions. The phase composition, unit-cell parameters, and thermal-reaction rates indicate nonstoichiometric Ag3 O was produced from the reaction of metastable, nonstoichiometric Ag2 O (cuprite structure) and ccp Ag. The thermal expansion of Ag3 O is anisotropic; below 25 °C, the a -axis expansion is about twice the c -axis expansion resulting in a negative slope of c / a ( T ). The reversal of the sign of c / a ( T ) near 25 °C is dramatic. The thermal reaction is arrested when the temperature is rapidly increased from ambient to 130 °C. Ag3 O is metastable and decreases its unit-cell volume during kinetic decomposition to Ag when heated above ambient temperature in air and nitrogen. The relative volume expansion of Ag3 O is about 80% less than Ag at room temperature and below. The suite of nonstoichiometric Ag3 O produced by heating displays a linear relation between c / a and unit-cell volume at room temperature. The c / a and unit-cell volume of a hydrothermally grown Ag3 O single crystal reported in a published structure determination was the Ag-rich, low-volume end member of the linear series. The c / a and unit-cell volume are sensitive indicators of the oxygen content and state of disorder.