Stability of (Cs, K)Al4Be5B11O28 (londonite) at high pressure and high temperature: a potential neutron absorber material

The stability and the thermo-elastic behaviour
of a natural londonite
½1a ðCs0:36K0:34Rb0:15Ca0:04Na0:02ÞR0:91
4eðAl3:82Li0:05Fe0:02ÞR3:89
4eðBe3:82B0:18ÞR4
12hðB10:97Be1Si0:01ÞR11:98O28
has been investigated up to 1,273(3) K (at 0.0001 GPa) and
up to 4.85(5) GPa (at 298 K) by means of in situ X-ray
powder diffraction. Up to 973 K, no evidence of phase
transition or anomalous thermo-elastic behaviour was
observed. At T[973 K, londonite shows the first evidence
of an irreversible structure destabilisation. The volume
thermal expansion coefficient between 298 and 973 K is
a0 = 2.38(6)10-5 K-1. Londonite shows an elastic
behaviour up to 4.85 GPa. No phase transition has been
observed within the pressure range investigated. P-V data
fitted with a second-order Birch-Murnaghan equation of
state give V0 = 389.1(1)A° 3 and KT0 = 280(12) GPa. On
the basis of the good thermo-elastic behaviour, substantiated
by the significantly low compressibility, the modest
thermal expansion up to 1,000 K and the significantly
high amount of boron (B2O3 * 50wt%), londonite-type
materials could be considered as potential inorganic host
for 10B in composite neutron-absorbing materials.