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High‐Pressure Behavior and Phase Stability of Al 5 BO 9 , a Mullite‐Type Ceramic Material
Author(s) -
Gatta G. Diego,
Lotti Paolo,
Merlini Marco,
Liermann HannsPeter,
Fisch Martin
Publication year - 2013
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.12411
Subject(s) - bulk modulus , mullite , phase transition , crystallography , materials science , diffraction , diamond anvil cell , tetragonal crystal system , compressibility , phase (matter) , x ray crystallography , octahedron , hydrostatic pressure , ceramic , crystal structure , chemistry , thermodynamics , composite material , physics , optics , organic chemistry
Phase stability, elastic behavior, and pressure‐induced structural evolution of synthetic boron‐mullite Al 5 BO 9 ( a = 5.6780(7), b = 15.035(6), and c =7.698(3) Å, space group Cmc 2 1 , Z = 4) were investigated up to 25.6(1) GPa by in situ single‐crystal synchrotron X‐ray diffraction with a diamond anvil cell (DAC) under hydrostatic conditions. No evidence of phase transition was observed up to 21.7(1) GPa. At 25.6(1) GPa, the refined unit‐cell parameters deviated significantly from the compressional trend, and the diffraction peaks appeared broader than at lower pressure. At 26.7(1) GPa, the diffraction pattern was not indexable, suggesting amorphization of the material or a phase transition to a high‐pressure polymorph. Fitting the P–V data up to 21.7(1) GPa with a second‐order Birch–Murnaghan Equation‐of‐State, we obtained a bulk modulus K T0 = 164(1) GPa. The axial compressibilities, here described as linearized bulk moduli, are as follows: K T0( a ) = 244(9), K T0( b ) = 120(4), and K T0( c ) = 166(11) GPa ( K T0( a ) : K T0( b ) : K T0( c ) = 2.03:1:1.38). The structure refinements allowed a description of the main deformation mechanisms in response to the applied pressure. The stiffer crystallographic direction appears to be controlled by the infinite chains of edge‐sharing octahedra running along [100], making the structure less compressible along the a ‐axis than along the b ‐ and c ‐axis.