Thermal and compressional behavior of the natural borate kurnakovite, MgB3O3(OH)5·5H2O

The thermal and compressional behaviors of kurnakovite, a potential B-rich aggregate in neutron radiation-shielding concretes, were studied by situ single-crystal synchrotron X-ray diffraction (100–393 K, 0–13.36(5) GPa). Above 393 the crystal structure collapses response to dehydration. bulk expansion coefficient is ?V(298K) = 5.18(1)?10?5 K?1. Volume trend modelled with Birch-Murnaghan equation state yields modulus KP0,T0 35(3) GPa. A phase transition occurs between 9.23(5) 11.11(5) GPa, leading triclinic high-P polymorph (with triple unit-cell volume) an increase coordination one third trigonal-planar boron sites tetrahedral geometry.