Hydrothermal Synthesis, Crystal Structure, and Spectroscopic Properties of Pure and Eu3+-Doped NaY[SO4]2 ∙ H2O and Its Anhydrate NaY[SO4]2

Abstract

The water-soluble colorless compound NaY[SO4]2 ∙ H2O was synthesized with wet methods in a Teflon autoclave by adding a mixture of Na2[SO4] and Y2[SO4]3 ∙ 8 H2O to a small amount of water and heating it up to 190 °C. By slow cooling, single crystals could be obtained and the trigonal crystal structure of NaY[SO4]2 ∙ H2O was refined based on X-ray diffraction data in space group P3221 (a = 682.24(5) pm, c = 1270.65(9) pm, Z = 3). After its thermal decomposition starting at 180 °C, the anhydrate NaY[SO4]2 can be obtained with a monoclinic crystal structure refined from powder X-ray diffraction data in space group P21/m (a = 467.697(5) pm, b = 686.380(6) pm, c = 956.597(9) pm, β = 96.8079(5), Z = 2). Both compounds display unique Y3+-cation sites with eightfold oxygen coordination (d(Y–Os = 220–277 pm)) from tetrahedral [SO4]2− anions (d(S–O = 141–151 pm)) and a ninth oxygen ligand from an H2O molecule (d(Y–Ow = 238 pm) in the hydrate case. In both compounds, the Na+ cations are atoms (d(Na–Os = 224–290 pm) from six independent [SO4]2− tetrahedra each. Thermogravimetry and temperature-dependent PXRD experiments were performed as well as IR and Raman spectroscopic studies. Eu3+-doped samples were investigated for their photoluminescence properties in both cases. The quantum yield of the red luminescence for the anhydrate NaY[SO4]2:Eu3+ was found to be almost 20 times higher than the one of the hydrate NaY[SO4]2 ∙ H2O:Eu3+. The anhydrate NaY[SO4]2:Eu3+ exhibits a decay time of about τ1/e = 2.3 µm almost independent of the temperature between 100 and 500 K, while the CIE1931 color coordinates at x = 0.65 and y = 0.35 are very temperature-consistent too. Due to these findings, the anhydrate is suitable as a red emitter in lighting for emissive displays.

Pilot-Scale Lanthanide Precipitation from Sulfate-Based Spent Ni-MH Battery Leachates: Thermodynamic-Based Choice of Operating Conditions

“…The above discrepancies observed between experimental and thermodynamic concentrations of Ce and Pr in solution are most likely due to the formation of a solid solution, where Ce 3+ and/or Pr 3+ would be inserted or substituted within the crystal structure of NaLa­(SO 4 ) 2 ·H 2 O and/or NaNd­(SO 4 ) 2 ·H 2 O. Theoretically, a solid solution could form given that the crystal structures of single phases of NaREE­(SO 4 ) 2 ·H 2 O (REE = La, Ce, Nd, or Pr) are all trigonal (space group P 3 2 21 or the enantiomorphic analogue P 3 2 21 ). − Moreover, the existence of solid solutions containing at least two REEs has previously been reported in the literature for other types of compounds such as rare earth oxides, nitrates, or phosphates . Additionally, several authors have reported that stable solid solutions are favorable for adjacent lanthanide pairs (i.e., La–Ce, Ce–Pr, Pr–Nd) in nitrate and phosphate systems.…”

Interactions of Na2SO4 and yttrium‐silicate environmental barrier coatings at 825°C

“…The reaction product Y 2 (SO 4 ) 3 in the presence of Na 2 SO 4 reacts, creating the double salt NaY(SO 4 ) 2 phase given by Equation (). This explains why most of the reaction product observed on the sample surface for the Y 2 SiO 5 coupons is the double salt phase. Equation () describes the double salt phase decomposition into Y 2 (SO 4 )O 2 and gaseous product Na 2 O(g) and SO 3 (g), which is shown to occur for NaY(SO 4 ) 2 around T ≥ 800°C 24 . NaY(SO 4 ) 2 may have increased stability at 825°C in the presence of SO 3 (g), which would drive Equation () to the left.…”

“…22,23 In addition, other RE sulfate reaction products are observed, most notably when RE 2 (SO 4 ) 3 reacts with Na + , creating double salt NaRE(SO 4 ) 2 reaction products. It is also reported that this double salt phase is soluble in Na 2 SO 4 -H 2 O systems at 25 • C. 24 Studies on the RE 2 (SO 4 ) 3 and NaRE(SO 4 ) 2 H 2 O phases show that they will decompose into an oxysulfate phase RE 2 (SO 4 )O 2 around 800 • C. The Y 2 (SO 4 )O 2 oxysulfate phase is reported to be stable at high temperatures, only to decompose around 1075 • C. 25,24 There are few existing reports of Na 2 SO 4 hot corrosion effects with RE-silicate EBCs. Na 2 SO 4 reactions with Yb 2 Si 2 O 7 were previously studied from 1000-1316 • C. These materials and temperatures were selected due to their relevance for RE-EBCs for SiC-CMC systems.…”

“…In addition, other RE sulfate reaction products are observed, most notably when RE 2 (SO 4 ) 3 reacts with Na + , creating double salt NaRE(SO 4 ) 2 reaction products. It is also reported that this double salt phase is soluble in Na 2 SO 4 ‐H 2 O systems at 25°C 24 . Studies on the RE 2 (SO 4 ) 3 and NaRE(SO 4 ) 2 H 2 O phases show that they will decompose into an oxysulfate phase RE 2 (SO 4 )O 2 around 800°C.…”

“…Studies on the RE 2 (SO 4 ) 3 and NaRE(SO 4 ) 2 H 2 O phases show that they will decompose into an oxysulfate phase RE 2 (SO 4 )O 2 around 800°C. The Y 2 (SO 4 )O 2 oxysulfate phase is reported to be stable at high temperatures, only to decompose around 1075°C 25,24 …”