The high-temperature behaviour of PuPO4 monazite and some other related compounds

Crystal chemistry of the monazite structure

“…All the light lanthanide phosphates (typically from lanthanum to gadolinium, including promethium 121 ) crystallize in the P2 1 /n space group of monazite [122][123][124][125][126][127][128][129] while the heavier (from Tb to Lu) adopt the zircon-type structure of xenotime. 118,[130][131][132] Nevertheless, for the rare earth elements located in the middle of the series, the limit between both families appears to be strongly dependent on the chemical way of synthesis.…”

BaAnIV(PO4)2 (AnIV = Th, Np) – A New Family of Layered Double Phosphates

“…Because of the steric compatibility of tetra- [ valent actinides with large divalent cations, most of the M II An IV (PO 4 ) 2 double phosphates discovered to date belong to this family. [8] In particular, CaTh(PO 4 ) 2 has attracted considerable interest for its ability to substitute tetravalent actinides (U IV , [9] Np IV , [10,11] and Pu IV to a lesser extent [12] ) by Th IV while keeping the remarkable thermal [13,14] and chemical [15][16][17][18][19][20][21][22][23] durability of the monazite structure. For these reasons, monazite-cheralite ceramics figure among the most serious candidates for long-term immobilization of nuclear waste containing minor actinides.…”

Phase study in Sr–Th–P–O system: Structural and thermal investigations of quaternary compounds

“…DTA curves of the three compounds did not show any phase transition up to 1573 K. In order to find out the final decomposition products, all the three compounds were heated in a furnace at 1673 K for 24 h and the XRD patterns of the end products confirm the formation of ThO 2 . Jardin et al [53] observed decomposition of CaTh(PO 4 ) 2 under inert atmosphere above 1473 K which led to the formation of ThO 2 . Though, it is reported in literature [33] that monoclinic SrTh(PO 4 ) 2 shows a phase transition at 1573 K, we could not observe any DTA peak during heating up to 1673 K.…”