  Studies at high pressures and temperatures are helpful for understanding the
physical properties of the solid state, including such classes of materials as,
metals, semiconductors, superconductors, or minerals. In particular, the phase
behaviour of ABX4 scintillating materials is a challenging problem with many
implications for other fields including technological applications and Earth
and planetary sciences. A great progress has been done in the last years in the
study of the pressure-effects on the structural and electronic properties of
these compounds. In particular, the high-pressure structural sequence followed
by these compounds seems now to be better understood thanks to recent
experimental and theoretical studies. Here, we will review studies on the phase
behaviour of different ABX4 scintillating materials. In particular, we will
focus on discussing the results obtained by different groups for the
scheelite-structured orthotungstates, which have been extensively studied up to
50 GPa. We will also describe different experimental techniques for obtaining
reliable data at simultaneously high pressure and high temperature. Drawbacks
and advantages of the different techniques are discussed along with recent
developments involving synchrotron x-ray diffraction, Raman scattering, and ab
initio calculations. Differences and similarities of the phase behaviour of
these materials will be discussed, on the light of the Fukunaga and Yamaoka and
the Bastide diagrams, aiming to improve the actual understanding of their
high-pressure behaviour. Possible technological and geophysical implications of
the reviewed results will be also commented.
