M. M. Godneva

Synthesis of zirconium (hafnium) fluoride compounds and their X-ray luminescence properties

Twenty-five zirconium (hafnium) fluoride compounds have been synthesized at room temperature in the systems MO2-H2SO4-M′nA(HF)-H2O (M = Zr (Hf); M′ = Na, K, Rb, Cs, NH4; A = F, SO4) and their X-ray luminescence spectra (luminescence wavelengths and relative intensities) have been measured. The X-ray luminescence of the compounds has been considered as a function of the composition (cations, anions, water content) and different structural factors (CNs, polyhedra, H-bonds). Ammonium compounds do not luminesce, and sodium fluorozirconates and heptafluorozirconates are weakly luminescing. Hexafluorozirconates M2Zr(Hf)F6 (M= K, Rb, Cs) and M5Zr4F21 · 3H2O (M = Rb, Cs), as well as oxofluorozirconate Rb2Zr3OF12, are strongly luminescing compounds.

ZrONO3)2-H3PO4-KF(HF)-H2O system at molar ratios of PO43−/Zr = 0.5−1.6 as the basis for phase formation

The system ZrO(NO3)2-H3PO4-KF(HF)-H2O was studied at ∼20°C along sections at molar ratios of PO43− = 0.5, 1.0, and 1.6; KF: Zr = 1−5; and HF: Zr = 2−6. Phases in precipitates were identified by X-ray powder diffraction; IR spectroscopy; and crystal-optical, chemical, X-ray fluorescence and thermal analyses. The following crystalline phases were isolated: potassium fluorozirconates K3ZrF7, K2ZrF6, δ-KZrF5, and KZrF5 · H2O; zirconium hydrophosphate Zr(HPO4)2 · 0.5H2O; and potassium fluorophosphate zirconate K3Zr3F3(HPO4)3(PO4)2. The following amorphous basic oxo(hydroxo)fluorohydrophosphate nitrates were isolated: K4Zr4O2.5F8(HPO4)2(NO3)3 · 6H2O, K2Zr3O3F2(HPO4)2(NO3)2 · H2O, and KZr3O1.5F3(HPO4)2(NO3)3 · 2H2O. Fields of solid phases were constructed, and the roles of anions and cations in the phase formation were considered.

Synthesis of rubidium fluorophosphatozirconates in the ZrO2-H3PO4-RbF-H2O system and their luminescent properties

Rubidium fluorophosphatozirconates (RFPZs) were synthesized along sections of the ZrO2-H3PO4-RbF-H2O system where PO43−/Zr = 1–2 (mol/mol) and RbF/Zr = 1–5 (mol/mol) and the initial solution contains 2–5 wt % ZrO2. The following RFPZs have been isolated for the first time: RbZrF2PO4 · 0.5H2O, Rb3H3Zr3F3(PO4)5, and RbZr3F4(PO4)3 · 1.5H2O. Their formation fields were determined. The compounds were characterized using powder X-ray diffraction, crystal-optical analysis, chemical analysis, electron probe microanalysis, thermal analysis, and IR spectroscopy. Luminescent properties of the compounds were measured. All RFPZs are orthophosphates, have high thermal durability, and X-ray luminescence (XRL). Rb3H3Zr3F3(PO4)5 has the highest XRL intensity.

Phase formation along the PO43−/Zr = 1.5–2.0 section of the ZrO(NO3)2-KF-H3PO4-H2O) system

The phase composition of precipitates at 20°C along the PO43−/Zr = 1.5–2.0 section at KF/Zr = 1–5 (mol/mol) of the ZrO(NO3)2-H3PO4-KF-H2O system has been investigated. Phases in these precipitates have been identified by X-ray powder diffraction, crystal-optical, chemical, and thermal analyses and by IR spectroscopy. The previously known potassium zirconates K3ZrF7 and K2ZrF6 have been revealed, and crystalline fluorophosphate zirconate K3Zr3F3(HPO4)3(PO4)2 and a phosphate nitrate of unknown formula have been obtained for the first time.

Synthesis and luminescent properties of alkali-metal and ammonium fluorosulfatozirconates and fluorosulfatohafnates

We have synthesized a variety of alkali-metal and ammonium fluorosulfatometallates (titanates, zirconates, and hafnates). The alkali fluorosulfatozirconates and fluorosulfatohafnates have been shown to exhibit efficient roentgenoluminescence (RL) in the UV through visible spectral region, with a maximum at 390–440 nm. Their RL spectra depend significantly on their composition (cation, anion, and water content), coordination of KF and K2SO4, and relative amounts of fluorine and SO4 groups. We have examined the effect of heat treatment on the RL of these compounds. The rubidium and cesium fluorosulfatozirconates Rb3Zr2F9SO4 · 2H2O, Cs2ZrF2(SO4)2 · 2H2O, Cs8Zr4F2(SO4)11 · 16H2O, and Cs2ZrF4SO4 offer the most efficient RL.

Phase formation in the HfO(NO3)2-H3PO4-CsF(HF)-H2O system

The phase formation in the system HfO(NO3)2-H3PO4-CsF(HF)-H2O was studied along the sections at the molar ratios PO43−/Hf = 0.5, 1.5, and 2.0 and RbF:Hf = 1–5, and also in the presence of HF at CsF: Hf = 1. The initial solutions contained 2–24 wt % HfO2. The synthesis was performed at room temperature. The following substances were isolated: crystalline cesium fluorophosphate hafnates CsHf2F6PO4 · 4H2O, CsHfF2PO4 · 0.5H2O, and CsH2Hf2F2(PO4)3 · 2H2O; X-ray amorphous cesium fluorophosphate hafnate of the average composition Cs2Hf3O1.5F5(PO4)2 · 5H2O; and X-ray amorphous cesium fluorophosphate nitrate hafnate Cs5H4Hf3F7(PO4)3.66(NO3)3 · 5H2O. The compositions of the amorphous phases should be refined. Cesium fluorophosphate hafnates were obtained for the first time. The compounds were studied by crystal-optical, elemental, X-ray diffraction, IR spectroscopic, and electron microscopic analyses.

Phase formation in the ZrO(NO3)2-H3PO4-CsF-H2O system at low concentration of the phosphorus-containing component

The ZrO(NO3)2-H3PO4-CsF-H2O system was studied at 20°C along the section at a molar ratio of PO43−/Zr = 0.5 (which is of the greatest interest in the context of phase formation) at ZrO2 concentrations in the initial solutions of 2–14 wt % and molar ratios of CsF: Zr = 1−6. The following compounds were isolated for the first time: crystalline fluorophosphates CsZrF2PO4 · H2O, amorphous oxofluorophosphate Cs2Zr3O2F4(PO4)2 · 3H2O, and amorphous oxofluorophosphate nitrate CsZr3O1.25F4(PO4)2(NO3)0.5 · 4.5H2O. The compound Cs3Zr3O1.5F6(PO4)2 · 3H2O was also isolated, which forms in a crystalline or glassy form, depending on conditions. The formation of the following new compounds was established: Cs2Zr3O1.5F5(PO4)2 · 2H2O, Cs2Zr3F2(PO4)4 · 4.5H2O, and Zr3O4(PO4)1.33 · 6H2O, which crystallize only in a mixture with known phases. All the compounds were studied by X-ray powder diffraction, crystal-optical, thermal, and IR spectroscopic analyses.

Phase formation along sections of the HfO(NO3)2-H3PO4-RbF-H2O system

The phase formation in the system HfO(NO3)2-H3PO4-RbF-H2O was studied along the sections at the molar ratios PO43−/Hf = 0.5, 1.0, 1.5, 2.0, and 3.0 and RbF: Hf = 1−5. The initial solutions contained 2–10 wt % HfO2. The synthesis was performed at room temperature. The following substances were obtained for the first time: crystalline fluorophosphatehafnate RbHfF2PO4 · 0.5H2O, crystalline triple salt HfF4 · Rb(PO4)0.33 · RbNO3, crystalline solvate Rb3Hf3(PO4)5 · 3HF, and amorphous fluorophosphate Hf3O2F2(PO4)2 · 8H2O (formula is conditional). The compounds were studied by crystal-optical, elemental, X-ray diffraction, thermogravimetric, IR spectroscopic, and electron microscopic analyses.

Phase formation in the ZrO(NO3)2-H2C2O4-KF-H2O system at 20°C

The system ZrO(NO3)2-H2C2O4-KF-H2O was studied in the sections C2O42− : Zr = 1 and 2. The following compounds were isolated: crystalline fluorooxalate zirconates K3ZrF5C2O4, K2ZrF4C2O4 · 2H2O, KZrF3C2O4 · 3H2O, and KZr2(OH)3F2(C2O4)2 · 4H2O, and also oxofluorozirconate K2Zr3O2.5F9 · 7H2O and oxofluoride oxalate Zr4O3F2(C2O4)4 · 2H2O. A crystalline phase and X-ray amorphous phases of undetermined compositions were detected. All the compounds, except K2ZrF4C2O4 · 2H2O, were obtained for the first time; the crystals KZrF3C2O4 · 3H2O, KZr2(OH)3F2(C2O4)2 · 4H2O, and K2Zr3O2.5F9 · 7H2O were mechanically picked up from a mixture of phases. The composition KZr2(OH)3F2(C2O4)2 · 4H2O is conditional. The phases were identified by X-ray powder diffraction, crystal-optical, and elemental analyses, and also by X-ray microanalysis and IR spectroscopy.

Phase formation in the ZrO(NO3)2-H3PO4-RbF-H2O system: the PO43−/Zr = 0.5 section

We studied phase formation in the ZrO(NO3)2-H3PO4-RbF-H2O system along PO43−/Zr = 0.5 (mol/mol) and RbF/Zr = 1–5 (mol/mol) sections with 2–10 wt % ZrO2 in the starting solution. We recovered amorphous rubidium oxofluorophosphatozirconate Rb2Zr3OF6(PO4)2 · 2H2O and the following fluorophosphatonitratozirconates: Rb2ZrF4(PO4)0.33NO3, which forms large cubic system crystals; weakly crystallized RbZr3OF3(PO4)2(NO3)2 · 5H2O; and amorphous Zr3OF3(PO4)2NO3 · (7–8) H2O. A shown by its IR spectrum, Rb2ZrF4(PO4)0.33NO3 contains NO3- and PO4 groups that are not coordinated to zirconium, meaning that this is a triple salt ZrF4 · Rb(PO4)0.33 · RbNO3. The formula units of the RbZr3OF3(PO4)2(NO3)2 · 5H2O and Zr3OF3(PO4)2NO3 · (7–8)H2O phases are only conventional. All compounds have been recovered for the first time.