• journal_title：American Mineralogist
• Contributor：Karl R. Whittle ; Neil C. Hyatt ; Katherine L. Smith ; Irene Margiolaki ; Frank J. Berry ; Kevin S. Knight ; Gregory R. Lumpkin
• Publisher：Mineralogical Society of America
• Date：2012-
• Format：text/html
• Language：en
• Identifier：10.2138/am.2012.3848
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：97
• issue：2-3
• firstpage：291
• section：Articles

Zirconolites based on the replacement of Ti⁴⁺ with equimolar amounts of Nb⁵⁺and Fe³⁺, CaZrTi_2−2x Nb_xFe_xO₇, have been jointly refined using high-resolution neutron powder diffraction and resonant X-ray powder diffraction data, with extra information provided from ⁵⁷Fe Mössbauer spectroscopy, to determine cation disorder. The results indicate that the CaZrTi_2−2xNb_xFe_xO₇ series adopts the zirconolite-2M polytype across the range, with the replacement of Ti⁴⁺ by Fe³⁺ and Nb⁵⁺ located within the hexagonal tungsten bronze (HTB) layers. Mössbauer spectroscopy shows that Fe³⁺ preferentially fills the Ti split (C2) site, with secondary filling of the C1 site and no observable occupancy of the C3 site. This has been confirmed by neutron and resonant X-ray diffraction. Niobium has been found to occupy both the C1 and C3 sites with no evidence for occupancy of the C2 site.