Increased Compressibility of Pseudobrookite-Type MgTi2O5 Caused by Cation Disorder
Robert M. Hazen,
*
Hexiong Yang
Compressibilities were determined for four pseudobrookite-type
magnesium titanate (MgTi2O5) samples
with different degrees of Mg-Ti disorder. Compressibilities of
a and c axes in disordered MgTi2O5 were 10% and 7% greater,
respectively, than those of a relatively ordered sample. The estimated
bulk moduli for fully ordered and disordered
MgTi2O5 are 167 ± 1 and 158 ± 1 gigapascals, respectively. This difference is an order of magnitude
greater than that predicted by bulk modulus-volume systematics. Cation order, in addition to composition and structure information, is thus
important when documenting the elasticity of crystalline phases.
Elastic constants of mantle silicates that are subject to
pressure-induced cation ordering must be reevaluated.
Geophysical Laboratory and Center for High Pressure Research,
Carnegie Institution of Washington, 5251 Broad Branch Road NW,
Washington, DC 20015, USA.
*
To whom correspondence should be addressed. E-mail:
hazen{at}gl.ciw.edu
