Synthesis, Symmetry, and Physical Properties of Cerium Pyrophosphate

Abstract

CeP 2 O 7 , a close structural relative of ZrP 2 O 7 , and many other M IV X 2 O 7 (X -P, V, As) phases, forms on heating Ce(HPO 4 ) 2 • xH 2 O between ∼300 and 600 °C and decomposes by oxygen loss at higher temperatures. In-situ X-ray diffraction measurements showed, for some precursor batches, the formation of CeP 2 O 7 in two distinct stages. At room temperature, CeP 2 O 7 is pseudocubic, but probably triclinic, displaying positive thermal expansion below ∼115 °C. Above this temperature, there is a transition to cubic symmetry (Pa3 j ) with the linear coefficient of thermal expansion going to zero at ∼450 °C and becoming negative at higher temperatures. CeP 2 O 7 probably undergoes two phase transitions on compression below ∼10.5 GPa. The phase existing between 0.65 and ∼5 GPa is soft with an average bulk modulus of ∼18 GPa.

Two Decades of Negative Thermal Expansion Research: Where Do We Stand?

“…High pressure studies in the ZrV 2 O 7 family have been limited to TiP 2 O 7 , ZrP 2 O 7 , CeP 2 O 7 , ZrV 2 O 7 and HfV 2 O 7 [103,111,112,113,114]. Interestingly, in situ diffraction experiments show no evidence for pressure-induced phase transitions or amorphization for TiP 2 O 7 and ZrP 2 O 7 , both of which are positive thermal expansion compounds.…”

Microwave-assisted rapid synthesis of cerium phosphates and their adsorption on uranium(VI)

“…Only a conventional calcination technique has been used to prepare CeP 2 O 7 and Ce(PO 3 ) 4 in previous studies [3,7,8,15,[29][30][31] 4 were adequately mixed in an agate mortar. The mixture was stored in a porcelain crucible with an insulation layer and directly irradiated at various MW powers for different times.…”

“…In recent years, considerable attention has been paid to rare earth phosphates because of their applications in novel functional materials, such as fluorescence materials [1,2], proton conductors [3][4][5][6], catalysts [7][8][9][10], magnetic cooling material [11], sunscreen materials [12][13][14], negative thermal expansion materials [15,16], and efficient adsorbents for radwaste [17][18][19]. Several phosphates such as Zr 2 O(PO 4 ) 2 , ZrP 2 O 7 and Th 4 (PO 4 ) 4 P 2 O 7 have been studied as potential substitutes for immobilization and long-term storage of uranium [18].…”

“…Several phosphates such as Zr 2 O(PO 4 ) 2 , ZrP 2 O 7 and Th 4 (PO 4 ) 4 P 2 O 7 have been studied as potential substitutes for immobilization and long-term storage of uranium [18]. Phosphates, especially rare earth phosphates, have poor solubility, strong irradiation resistance, excellent thermal stability, good binding ability with actinide elements, and high adsorption capability on actinide elements and heavy metals [15][16][17][18][19][20][21][22][23][24][25][26][27][28]. For this reason, rare earth phosphates as adsorbents are expected to play a significant role in the safety of underground radwaste repositories due their potential use for an engineered containment barrier.…”

Effect of partial substitution of Sn4+ by M4+ (M=Si, ti, and Ce) on sinterability and ionic conductivity of SnP2O7

“…Though the cerium pyrophosphates are thermally unstable at 4400 1C and therefore their sintering at the higher temperature is avoided [10,11], it has been observed that they give fairly dense specimens even on sintering at temperatures $ 400 1C [5,[8][9][10][11]. Considering the fact that pyrophosphates of cerium and tin are generally isomorphous, with both having cubic lattice and Pa3 space group [12,13], it is expected that on partially replacing Sn 4 þ ion in SnP 2 O 7 by Ce 4 þ ion, Ce 4 þ ion would be easily incorporated into tin pyrophosphate lattice, although the ionic radius of Ce 4 þ ion (r=0.87 Å) is larger than that of Sn 4 þ ion (r=0.69 Å) [14], and improve the sinterability of tin pyrophosphate. Therefore, in this work, we have doped tin pyrophosphate with (0-10%) CeO 2 and analyzed its effect on the phase composition, sinterability and microstructure, and ionic conductivity.…”