NZP Structure Research Articles

Novel kosnarite-based M0.5Zr2(AsO4)x(PO4)3-x (M – Sr, Ba and Cd) ceramics for radwaste incorporation

Mineral-like single-phase NZP materials of variable composition M0.5Zr2(AsO4)x(PO4)3−x (M − Sr, Ba, Cd) are of interest as matrices for isolation of high-level Sr, Ba and Cd wastes generated during reprocessing of irradiated nuclear fuel. Such polycrystalline phases were synthesized by sol-gel method with subsequent heat treatment and investigated by X-ray diffraction, IR spectroscopy and electron-probe microanalysis. Rietveld structure refinement showed that the framework is formed by ZrO6 octahedra and mixed AsO4/PO4 tetrahedra connected by vertices; Sr, Ba or Cd cations are located in extra-framework positions. Arsenate-phosphates can be classified as medium thermal expansion materials due to their average coefficient of linear thermal expansion of 2.8∙10−6 °C−1. Chemical durability test indicates that the leaching rate of Sr2+ ions from the NZP structure type solid solution is of the order of 10−5 g cm−2d−1.

Study of the chemical stability of Sr<sub>0.5</sub>Zr<sub>2</sub>(PO<sub>4</sub>)<sub>3 </sub> phosphate with a cosnarite structure in various environments

Samples of ceramics based on Sr0.5Zr2(PO4)3 phosphate with the structure of the kosnarite mineral (NaZr2(PO4)3, NZP) were obtained by electric pulse plasma sintering. Submicron phosphate powders with particle sizes less than 1 μm were obtained by the sol-gel method. Powders and ceramics have a single-phase NZP structure. The relative density of the ceramics was 97.6%. The chemical stability of the obtained ceramics was studied in static mode at 90°C in distilled and mineral water and in acidic and alkaline environments. The minimum achieved leaching rates were ~10-4-10-6 g/(cm2 day). The in uence of the contact environment on the rate and mechanism of Sr leaching from Sr0.5Zr2(PO4)3 ceramic samples within 42 days was studied. It has been shown that Sr leaching occurs due to the dissolution of the surface layer of ceramics when tested in distilled water and in mineral water (up to 7 days) and due to Sr leaching from the open ceramic surface after 7 days of testing in mineral water.

Synthesis and Investigation of Na1 – xR0.33xTiO2(PO4)3 (R = Y or La) Phosphates

Phosphates Na1 – xR0.33xTi2(PO4)3 (R = Y or La; 0 ≤ х ≤ 1) were synthesized by the Pechini process and characterized by X-ray diffraction, electron microscopy with microprobe analysis, and IR spectroscopy. The systems exhibit isodimorphism to form a series of solid solutions belonging to the NaZr2(PO4)3 (NZP) structural type and crystallizing in space group Rc or RThe Rietveld structural studies confirmed the isomorphic miscibility of sodium and the rare-earth element in the interstices of the NZP structure. The unit cell parameter с in the phosphates studied tends to increase, and the parameter а tends to decrease, in response to rising temperature, which trends are typical of NZP phosphates.

Facile synthesis of calcium magnesium zirconium phosphate adsorbents transformed into MZr4P6O24 (M: Ca, Mg) ceramic matrix for radionuclides immobilization

Calcium zirconium CaZr4P6O24 and magnesium zirconium MgZr4P6O24 phosphates with NZP structure are promising materials for the safe disposal of high radioactive wastes. Herein, firstly the facile synthesis of calcium magnesium zirconium phosphate adsorbents transformed into MZr4P6O24 (M: Ca, Mg) ceramic matrix as effective materials for radionuclides adsorption and immobilization was developed. The detailed analysis of phase composition, functional groups, elements content, surface morphology, texture and adsorption characteristics of prepared calcium magnesium zirconium phosphates were performed. It was shown that obtained samples were amorphous materials. The high efficacy (K d > 104cm3/g) of prepared adsorbents towards 137Cs, 85Sr, 60Co radionuclides in the wide pH range of 4.0–10.0 was demonstrated. The formation of calcium zirconium CaZr4P6O24 and magnesium zirconium MgZr4P6O24phosphates with zirconia ZrO2admixture during adsorbents calcination at 1000 °C was shown. The obtained results have high capabilities for the development of effective calcium magnesium zirconium phosphate adsorbents for radionuclides immobilization into MZr4P6O24(M: Ca, Mg) ceramic matrix.

Pb0.5 + xMgxZr2 – x(PO4)3(x = 0, 0.5) Phosphates: Structure and Thermodynamic Properties

Abstract—Crystalline Pb0.5 +xMgxZr2 –x(PO4)3 (x = 0, 0.5) phosphates of NaZr2(PO4)3 (NZP) structural type were synthesized. The heat capacity of Pb0.5Zr2(PO4)3 was measured by adiabatic vacuum and differential scanning calorimetry (DSC) within the temperature range 8–660 K. The studied phosphates were found to experience a reversible phase transition in the region 256–426 K. According to the results of Rietveld structural study, this transition occurred due to an increase in disorder of lead cation positions in cavities of the NZP structure. The measurements of PbMg0.5Zr1.5(PO4)3 heat capacity in the temperature range 195–660 K showed that it experienced a similar phase transition at 255–315 K. Based on the measured experimental data, the thermodynamic functions of Pb0.5Zr2(PO4)3, such as $$C_{p}^{0}(T),$$ [H0(T) – H0(0)], S0(T), and [G0(T) – H0(0)] were calculated for the temperature range 0–660 K. The standard formation enthalpy of Pb0.5Zr2(PO4)3 was determined at 298.15 K.

The Synthesis and Thermal Expansion Behavior of Sodium and Calcium Zirconium Copper Phosphates

The crystal-chemical approach has been applied to design materials with regulated thermal expansion. To that end, model simulations have been performed for compositions of phosphates that yield solid solutions of the following type Na1 + 2xZr2 –xCux(PO4)3 and Ca0.5 +xZr2 –xCux(PO4)3, 0.1 ≤ x ≤ 0.5 with the expected structure of NaZr2(PO4)3 (NZP). The new phosphates have been prepared by solid-state reactions and characterized by X‑ray diffraction, IR spectroscopy, and scanning electron microscopy. The compounds have been shown to crystallize in the NZP structure, with a particle size from 0.1 to 1 μm. The thermal expansion of the compounds has been studied by high-temperature X-ray diffraction in the temperature range from 25 to 700°C. Linear, average, and volume coefficients of thermal expansion and anisotropy of thermal expansion have been calculated and analyzed in relation to composition of Na, Zr, Cu and Ca, Zr, Cu phosphates in the studied sets.

Mechanical and thermal expansion studies on Ca0.5Sr0.5Zr4-xTixP6O24 ceramics

Ca0.5Sr0.5Zr4-xTixP6O24 (x = 0−0.2) ceramics belonging to the NZP family were prepared and dense ceramics with no microcracks were obtained. All of the ceramic samples were still composed of the typical NZP structure with a small amount of Ti4+ substitution for Zr4+. The mechanical and thermal expansion properties of the ceramics were characterized and the result showed that the flexural strength monotonically increased to 66.5 MPa. The thermal expansion coefficient varied from 1.8 to 3.4 × 10−6/°C with Ti4+ content increasing. Thus, it was clear that the substitution of Ti4+ for Zr4+ had obvious effects on the sinterability, mechanical and thermal expansion properties of Ca0.5Sr0.5Zr4-xTixP6O24 ceramics, which were discussed in detail.

New Phosphate-Sulfates with NZP Structure

NaZr2–xBx(PO4)3–2x(SO4)2x (0 ≤ x ≤ 1.25, B = Mg, Co, Ni, Cu, Zn), and NaZr2–xRx(PO4)3–x(SO4)x (0 ≤ x ≤ 1.25, R = Al, Fe) phosphate-sulfates series have been prepared by a sol–gel process. These compounds belong to the NaZr2(PO4)3 (NZP) structure family and crystallize in hexagonal crystal system, space group R $$\bar 3$$ c. Limited solid solution series were found to exist; their formation temperatures and thermal stability limits were determined. Particle sizes as determined by microstructure observation were 50–200 nm, and for Cu- and Zn-containing samples, 200–500 nm. The thermal expansion of phosphate-sulfate NaZr1.25Cu0.75(PO4)1.5(SO4)1.5 was studied in the range 25–700°C. Thermal expansion coefficients and thermal expansion anisotropy were found to be αa =–5.40 × 10–6 °C–1, αс = 18.88 × 10–6 °C–1, αavg = 2.69 × 10–6 °C–1, and Δα = 24.28 × 10–6 °C–1.

Synthesis and study of Cd0.5 + x M x Zr2‒x (PO4)3 (M = Mg, Co, Mn) phosphates

New phosphates Cd0.5 + xMxZr2‒x(PO4)3 (M = Mg, Co, Mn) have been prepared by sol–gel method. The formation of limited solid solutions Cd0.5 + xMxZr2‒x(PO4)3 of the NaZr2(PO4)3 (NZP) structural type, 0 ≤ x ≤ 0.6 for М = Mg and 0 ≤ х ≤ 0.3 for M = Co and Mn, has been found using X-ray diffraction, IR spectroscopy, and electron microprobe analysis. The distribution of cations in the 2+ oxidation state over crystallographic positions of the NZP structure has been shown in the phosphate CdMg0.5Zr1.5(PO4)3. It has been found that half of framework-forming octahedral positions in the structure of the latter are occupied by Zr4+ cations and the other half are randomly occupied by Zr4+ and Cd2+ ions. The Cd2+ and Mg2+ ions alternately occupy the positions of structure cavities. The thermal expansion of CdMg0.5Zr1.5(PO4)3 in a temperature range of 25‒800°C has been studied. The phosphate is found to be among the medium expanding substances.

Phase Formation, Structure, and Thermal Expansion of Phosphates M0.5(1 + x)Fe x Ti2–x (PO4)3 (M = Mn, Zn)

Phosphates M0.5(1 + x)Fe x Ti2–x (PO4)3 (M = Mn, Zn; 0 ≤ x ≤ 2) were synthesized by coprecipitation of salts from aqueous solutions with subsequent heat treatment. Their phase formation was studied; fields of concentration and temperature stability of solid solutions of the NaZr2(PO4)3 (NZP) structural type were identified. Comparison of the results of this work with the previously obtained data on the phase formation of isoformular phosphates with M = Co, Ni, Cu showed that the size of the homogeneity regions of solid solutions in the systems M0.5(1 + x)Fe x Ti2–x (PO4)3 (M = Mn, Co, Ni, Cu, Zn) increases with increasing radius of the cation in the oxidation state +2. The crystal structure of phosphate MnFeTi(PO4)3 was studied. It was demonstrated that Fe3+ and Ti4+ are randomly distributed over positions in the framework of the NZP structure, and Mn2+ cations occupy extraframework positions of the M1 type within columns of polyhedra. The average thermal expansion coefficient αav = 4.8 × 10–6 °С–1 of MnFeTi(PO4)3 suggests that the studied phosphate is a medium-expandable substance.

Temperature induced phase transition of CaMn0.5Zr1.5(PO4)3 phosphate

In this work we investigated the structural behaviour of a CaMn0.5Zr1.5(PO4)3. Due to the presence of divalent Mn2+ cations this compound can possess interesting luminescence properties. It was recently understood that this phosphate undergoes a temperature induced irreversible phase transition in the range of 800–875°C. It has also been shown that the 3d–3d luminescence of Mn2+ increases 10 fold for the high temperature polymorph. To determine the Mn environment structural investigations of both phases have been performed by the X-ray powder diffraction and Raman spectroscopy methods. The low temperature modification adopts the trigonal NZP structure type with a slightly lower symmetry (space group R32, a=8.7850(2)Å, c=22.6496(7)Å, V=1514.8(1)Å3). The high temperature form in turn has orthorhombic symmetry (space group Pnma, a=6.2350(3)Å, b=6.6281(3)Å, c=14.4731(6)Å, V=598.13(5)Å3). Both structures were solved ab-initio from powder data and structural analysis was performed. In-situ and RT Raman spectra are consistent with the XRD derived structural model. Mn2+ cations occupy different types of positions in these structures and a change in Mn coordination number (6 for LT phase, 7 for HT phase) results in different Mn–O bond lengths. These differences may explain the change in the optical properties between the polymorphs.

Phosphates having the NaZr2(PO4)3 structure and containing titanium (or zirconium) and elements in oxidation degree 2+ (calcium or zinc)

Complex phosphates Ca0.5 + x Zn x E2 − x (PO4)3 (E = Ti, Zr) having NaZr2(PO4)3 (NZP) structure have been prepared and characterized by X-ray diffraction, electron probe microanalysis, IR spectroscopy, and differential thermal analysis (DTA). Their phase formation has been studied by X-ray powder diffraction and DTA. The concentration and temperature fields of existence of these NZP phases have been determined: substitution solid solutions exist in the range of compositions where 0 ≤ x ≤ 0.5. The Ca0.7Zn0.2Ti1.8(PO4)3 crystal structure has been refined by the Rietveld method (space group \(R\bar 3\), a = 8.3636(4) A, c = 21.9831(8) A, V = 1331.7(1) A3, Z = 6). The framework in the NZP structure is built of octahedra, which are populated by titanium and zinc atoms, and PO4 tetrahedra. Calcium atoms occupy extraframework positions. Extensive solid solution formation due to the accommodation of cations(2+) in the interstices within the NZP framework (M) and in the framework-forming octahedra (M′) makes it possible to design a plurality of new M0.5 + x M′ x E2 − x (PO4)3 phosphates with tailored structures.

Immobilization of lanthanum, cerium, and selenium into ceramic matrix of sodium zirconium phosphate

The crystallographic nature of NaCe0.2Zr1.8P3O12, NaSe0.2Zr1.8P3O12, and NaLa0.13Ce0.14Se0.15·Zr1.58P3O12 phases has been investigated with the aim of developing methods for radionuclide immobilization into sodium zirconium phosphate (NZP) phase. The phases have the NZP structure, space group \(R\bar 3c\), Z = 6. Powder diffraction data have been subjected to Rietveld refinement, and satisfactory structural convergence of R-factors was achieved. The PO4 stretching and bending vibration bands in the IR region have been assigned.

Comparison of sodium zirconium phosphate and calcium zirconium phosphate structures for the retention of fluoride

Fluoride anion interaction has been explored for the first time to investigate how the structure of sodium zirconium phosphate (NZP) and calcium zirconium phosphate (CZP) can be altered in its presence. Different compositions were made by adding NaF and CaF2 in CZP and NZP matrices respectively. Fluoride interaction differs with NZP and CZP structure as suggested by F-NMR data. The addition of fluoride to the NZP or CZP structure enables to stabilize the structure at a low temperature of 600–700 °C under microwave conditions.

Solid ceramic based on mixed-frame titanium phosphate and calcium synthesized in solar furnace

The authors synthesized of mixed orthophosphates Ca0.5Ti2(PO4)3 using concentrated solar radiation. We obtained a porous ceramic filter with the given type of NZP structure and high thermal and hydrolytic stability.

Microfiltration NZP ceramic based on network alkaline-earth phosphates

A solar furnace based technology for high-temperature synthesis of NZP structure was implemented. X-ray phase analysis was used to study phase-formation in the systems obtained. It was determined that the Ca, Sr, and Ba phosphates obtained by melting belong to an NZP-type structural group. It was shown experimentally that strong porous monophase NZP ceramics can be obtained by conventional sintering.

Encapsulation of heterovalent ions of two simulated high-level nuclear wastes and crystallization into single-phase NZP-based wasteforms

Preliminary data were obtained on the immobilization of various heterovalent ions present in the two selected high-level nuclear waste compositions. The entire set of ions present in the waste compositions were immobilized into sodium zirconium phosphate (NZP) structure. The waste loading was in the range 5–25%. The two types of wasteforms loaded with the simulated high-level waste compositions were characterized by powder X-ray diffraction, FT-IR, TGA/DTA, and scanning electron microscopy. The difference in the compositions of the two simulated wastes was reflected in the waste loading percentage and the crystallization of the wasteforms into NZP structure. Up to 12% waste loading, single phase isostructural with NZP was obtained as a major product in the case of the first waste composition. An increase in the waste loading led to the segregation of ZrP2O7 as a secondary phase. With the second waste composition, an NZP-like phase was obtained as the major product even at 25% waste loading.

Erbium zirconium phosphate Er0.33Zr2(PO4)3 of the NaZr2(PO4)3 family. Structure contraction on heating

Erbium zirconium phosphate Er0.33Zr2(PO4)3, a member of the family of structural analogs of NaZr2(PO4)3 (NZP), was prepared by the sol-gel process and studied by X-ray phase analysis, IR spectroscopy, and differential scanning calorimetry. The behavior of erbium zirconium phosphate on heating in the temperature interval from 25 to 625°C was studied by high-temperature X-ray diffraction. Expansion and contraction along different crystallographic directions and contraction of the structure as a whole were found. The overall contraction is due to higher contribution of the negative axial thermal expansion coefficients αa and αb to αav and hence to the volume expansion of the phosphate. On heating to 900°C, the NZP structure is preserved.

Crystallographic evaluation of sodium zirconium phosphate as a host structure for immobilization of cesium

Sodium zirconium phosphate (NZP) is a potential material for immobilization of nuclear effluents. The existence of cesium containing NZP structure was determined on the basis of crystal data of solid solution. It was found that up to ~9.0 wt% of cesium could be loaded into NZP formulations without significant changes of the three-dimensional framework structure. The crystal chemistry of Na1−xCsxZr2P3O12 (x = 0.1–0.4) has been investigated using General Structure Analysis System programming. The CsNZP phases crystallize in the space group R-3c and Z = 6. Powder diffraction data have been subjected to Rietveld refinement to arrive at a satisfactory structural convergence of R-factors. The unit cell volume and polyhedral (ZrO6 and PO4) distortion increase with rise in the mole% of Cs+ in the NZP matrix. The PO4 stretching and bending vibrations in the infrared region have been assigned. SEM, TEM, and EDAX analysis provide analytical evidence of cesium in the matrix.

Facile Chemical Insertion of Lithium in Eu0.33Zr2(PO4)3—An Elegant Approach for Tuning the Photoluminescence Properties

Insertion of lithium in EuIII0.33Zr2(PO4)3 having NZP structure, using n-butyllithium, has allowed a mixed valent phosphate Li0.1EuII0.1EuIII0.23Zr2(PO4)3 to be synthesized. The presence of mixed valent Eu gave rise to PL emission in the blue-green (Eu2+) and red (Eu3+) regions under 393 nm excitation with the chromaticity coordinates close to ideal white light.