• journal_title：American Mineralogist
• Contributor：Aaron C. Palke ; Jonathan F. Stebbins ; Dan J. Frost ; Catherine A. McCammon
• Publisher：Mineralogical Society of America
• Date：2012-11-01
• Format：text/html
• Language：en
• Identifier：10.2138/am.2012.4101
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：97
• issue：11-12
• firstpage：1955
• section：Articles

We present ²⁷Al and ²⁹Si magic angle spinning nuclear magnetic resonance (MAS-NMR) spectra of Al- and Fe-bearing, high-pressure pyroxene and perovskite samples, synthesized in a multi-anvil apparatus at 26 GPa and 1900 °C at targeted compositions of (Mg_1−xFe_x)(Si_1−xAl_x)O₃ (x = 0.01, 0.025, and 0.05). ²⁷Al MAS-NMR spectra of the perovskite samples indicate that Al³⁺ replaces both Si⁴⁺ in the octahedral site and Mg²⁺ in the larger 12-coordinated site. NMR signal loss caused by paramagnetic interactions is often a severe complication when performing NMR on materials containing Fe^2+,3+; however, careful measurement of signal loss and comparison to total Fe content in these samples sheds light on the nature of Al and Fe incorporation. NMR signal loss for the pyroxenes is linearly related to total Fe content as would be expected in the case of uncorrelated substitution of randomly distributed Al and Fe. However, ²⁷Al signal loss for the perovskite samples increases only slightly between samples with x = 0.01 and 0.025 indicating similar coordination of Al by Fe and non-random distribution. Complete signal loss at Fe/(Fe + Mg) = 0.05 suggests the upper limit of Fe²⁺ and Fe³⁺ concentration at which useful NMR data can be obtained for this system.