PO4 Solid Solution Research Articles

Elucidating the Impact of Mn-Fe Substitution on The Crystal Structure of LiMn(x)Fe(1-x)PO4 Solid Solutions: A Theoretical Study

Abstract This study generated crystallography information files (CIF) to synthesize LiMn(x)Fe(1-x)PO4 solid solutions, with the Mn to Fe substitution ratio (x) ranging from 0 to 1 in 0.1 increments, guided by Vegard’s law, utilizing crystallography software. The investigation focused on how this substitution influences key structural parameters and properties within the Mn-Fe Olivine system. Specifically, it examined variations in lattice parameters, unit cell volume, cell density, and Theoretical capacity attributable to the substitution factor. Furthermore, X-ray diffraction (XRD) patterns, predicted using mathematical models through the same software, provided insights into structural changes. Notably, the XRD analysis revealed a progressive shift in peak positions and an increase in peak intensities corresponding to the substitution level. These observations were linked to the altered lattice parameters resulting from the introduction of ions with varying ionic radii, and an enhanced electron density stemming from the increased presence of Fe. This comprehensive analysis underscores the significant impact of Mn-Fe replacement on the microstructural characteristics and electron density of the olivine system, offering valuable insights into material design and optimization in the context of energy storage materials.

Structural consideration on Eu2+ distribution inside glaserite-type Na(Ba, Sr)PO4: Eu2+ phosphor: High-intensity and broadband emission consisting of three overlapping Eu2+ emission bands

Glaserite-type NaBaPO4: Eu2+ phosphor has attracted considerable attention because of the intense blue emission. Although this emission was discussed under the assumption that Eu2+ ions were distributed only in A- and B-sites of the crystal structure, this assumption has proved inconsistent with previous results and hindered the quantitative evaluation of the emission. This study aims to quantitatively interpret the emission characteristics in Eu2+-activated Na(Ba, Sr)PO4 solid solutions by tracking spectroscopic changes resulting from the modifications in the crystal structure when Ba2+ in NaBaPO4 is replaced by Sr2+. The broadband emission observed in Na(Ba, Sr)PO4: Eu2+ consists of three partially overlapping bands. Electron spin resonance (ESR) spectroscopy reveals that the three bands correspond to 4f65 d1-4f7 interconfigurational electron transitions in crystallographically distinct three Eu2+. The distribution in three sites has not been observed in M3MgSi2O8 or A2MMgP2O8 (A: Li, Na, M: Ba, Ca, Sr), and specific to NaBaPO4 host. Because the emission wavelengths of the three Eu2+ ions are close, NaBaPO4: Eu2+ exhibits a high resultant emission intensity. Based on the Eu2+’s preference for sites with high Sr2+ occupancy, Eu2+ distribution and the associated Na(Ba, Sr)PO4: Eu2+ emission color can be tailored through Ba2+/Sr2+ replacement. The structure-emission relationship revealed in this study provides valuable insights for designing high-luminous-efficiency in glaserite-type phosphors.

Transition mechanism and thermokinetic analysis of Sr0.5Zr2(PO4)3–Ce0.5Sm0.5PO4 composite ceramics for nuclear waste forms based on in-situ synthesis

In this study, the novelly designed Sr0.5Zr2(PO4)3–Ce0.5Sm0.5PO4 composite ceramics were utilized as nuclear waste form to simultaneously immobilize simulated fission products Sr and actinide nuclides. The phase transition mechanism, thermokinetics and densification behavior of Sr0.5Zr2(PO4)3–Ce0.5Sm0.5PO4 composite ceramics based on in-situ synthesis were systemically analyzed by XRD, in-situ XPS, TG-DSC, SEM and density measurements. The results demonstrate that the formation of Ce0.5Sm0.5PO4 solid solution phase preceded that of Sr0.5Zr2(PO4)3 phase, of which there is a valence change of Ce from Ce4+ to Ce3+ before 1023 K. Additionally, as for the exothermic crystallization enthalpy, change of exothermic crystallization enthalpy and activation energy, the values of Sr0.5Zr2(PO4)3 and Ce0.5Sm0.5PO4 phases in composite ceramics are 286.17 – 515.61 mJ, 19.11 – 35.38 J/g, 702.45 kJ/mol and 145.21 – 232.44 mJ, 9.26 – 15.44 J/g, 450.04 kJ/mol, respectively. It is then indicated that the formation of Ce0.5Sm0.5PO4 phase is definitely more favorable than that of Sr0.5Zr2(PO4)3 phase. Simultaneously, the relative densities of Sr0.5Zr2(PO4)3–Ce0.5Sm0.5PO4 composite ceramics are more than 95 % when the sintering temperature exceeds 1273 K.

High quality of LiMg0.9Zn0.06Ni0.04PO4-TiO2 microwave ceramic and its application for 5G dielectric waveguide bandpass filter

A new microwave dielectric composite ceramic (1-x) wt%LiMg0.9Zn0.06Ni0.04PO4-x wt%TiO2 (0 ≤ x ≤ 18 wt%) was synthesized in the low sintering temperature range of 850 °C − 975 °C by the solid-state reaction method. The XRD diffractogram confirmed the coexistence of LiMg0.9Zn0.06Ni0.04PO4 and TiO2, and no second phase was detected. Due to their opposite τf values, the τf values of LiMg0.9Zn0.06Ni0.04PO4 solid solution ceramics were adjusted by adding different volume fractions of TiO2. The composite ceramic with x = 15 wt% sintered at 975 °C shows desirable microwave dielectric properties of εr∼10.30, Q×f ∼ 58,400 GHz (tan δ = 2.093 ×10−4), and τf ∼ + 4.04 ppm/ °C (at ∼12 GHz). Based on the 85 wt% LiMg0.9Zn0.06Ni0.04PO4-15 wt% TiO2 ceramics, a fourth order dielectric waveguide filter filled with composite ceramics is designed and packaged for the RF front-end of the China Mobile 5 G base station. The test results show that the center frequency of the filter is 4.65 GHz, the working bandwidth is 300 MHz, the filter has a good out of band rejection capability, and the insertion loss in band is 0.18 dB. Combined with the filter test data and material performance, the designed dielectric waveguide filter meets the communication requirements of the base station, and the higher Q×f microwave dielectric ceramic material can achieve low insertion loss and excellent frequency selection performance of the filter.

Zero Lithium Miscibility Gap Enables High-Rate Equimolar Li(Mn,Fe)PO4 Solid Solution.

Forming olivine-structured Li(Mn,Fe)PO4 solid solution is theoretically a feasible way to improve the energy density of the solid solutions for lithium ion batteries. However, the Jahn-Teller active Mn3+ in the solid solution restricts their energy density and rate performance. Here, as demonstrated by operando X-ray diffraction, we show that equimolar LiMn0.5Fe0.5PO4 solid solution nanocrystals undergo a single-phase transition during the whole (de)lithiation process, with a feature of zero lithium miscibility gap, which endows the nanocrystals with excellent electrochemical properties. Specifically, the energy density of LiMn0.5Fe0.5PO4 reaches 625 Wh kg-1, which is 16% higher than that of LiFePO4. Moreover, the high-performance LiMn0.5Fe0.5PO4 nanocrystals are prepared by a microwave-assisted hydrothermal synthesis in pure water.

Experiment and calculation: The Li(Zn, Mn)PO4 solid solution ceramics with low dielectric constant, high quality factor, and low densification temperature

Abstract The microstructure, sintering and microwave dielectric properties of (1−x)LiZnPO4+xLiMnPO4 (x = 0.0–1.0) composite ceramics were discussed specifically through density functional theory calculation and solid-state reaction experiment. The (1−x)LiZnPO4+xLiMnPO4 (x = 0.0–1.0) composite ceramics were characterised using network analyser, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and differential–thermal and thermo-mechanical analyser. The solid solution of Mn2+-ion-doped LiZnPO4 ceramic and Zn2+-ion-doped LiMnPO4 ceramic formed when the LiMnPO4 ceramic was added into the LiZnPO4 ceramic. The modification of the bond length, bond population and electron density could be observed in the ZnO4 tetrahedron and MnO8 octahedron. Moreover, the densification window of the LiZnPO4 ceramic decreased slightly. Experimental results were specifically explicated by the calculation result. Peak dielectric properties were obtained when x = 0.3 sintered at 800 °C, er = 5.83, Q × f = 71,007 GHz, τf = −82.84 ppm/°C and relative density = 97.33%. The addition of the LiMnPO4 ceramic is an effective method for improving the sintering and microwave dielectric properties of the LiZnPO4 ceramic.

A Spectroscopic Investigation of Eu3+ Incorporation in LnPO4 (Ln = Tb, Gd1-xLux, X = 0.3, 0.5, 0.7, 1) Ceramics.

We have investigated the incorporation of the luminescent Eu3+ cation in different LnPO4 (Ln = Tb, Gd1−xLux, x = 0.3, 0.5, 0.7, 1) host phases. All samples were analyzed with powder X-ray diffraction (PXRD), Raman spectroscopy, and site-selective time-resolved laser-induced luminescence spectroscopy (TRLFS) directly after synthesis and after an aging time of one year at ambient conditions. The PXRD investigations demonstrate the formation of a TbPO4 phase in an uncommon anhydrite-like crystal structure evoked by a pressure-induced preparation step (grinding). In the Gd1−xLuxPO4 solid solution series, several different crystal structures are observed depending on the composition. The TRLFS emission spectra of LuPO4, Gd0.3Lu0.7PO4, and Gd0.5Lu0.5PO4 indicate Eu3+–incorporation within a xenotime-type crystal structure. TRLFS and PXRD investigations of the Gd0.7Lu0.3PO4 composition show the presence of anhydrite, xenotime, and monazite phases, implying that xenotime no longer is the favored crystal structure due to the predominance of the substantially larger Gd3+–cation in this solid phase. Eu3+–incorporation occurs predominantly in the anhydrite-like structure with smaller contributions of Eu3+ incorporated in monazite and xenotime. The electronic levels of the Eu3+–dopant in Gd0.3Lu0.7PO4 and Gd0.5Lu0.5PO4 xenotime hosts are strongly coupled to external lattice vibrations, giving rise to high-energy peaks in the obtained excitation spectra. The coupling becomes stronger after aging to such an extent that direct excitation of Eu3+ in the xenotime structure is strongly suppressed. This phenomenon, however, is only visible for materials where Eu3+ was predominantly incorporated within the xenotime structure. Single crystals of Eu3+–doped LuPO4 show no changes upon aging despite the presence of vibronically coupled excitation peaks in the excitation spectra measured directly after synthesis. Based on this observation, we propose a lattice relaxation process occurring in the powder samples during aging, resulting in Eu3+ migration within the crystal structure and Eu3+ accumulation at grain boundaries or xenotime surface sites.

Structural characterization of (Sm,Tb)PO4 solid solutions and pressure-induced phase transitions

Sm1-xTbxPO4 solid solutions were synthesized and extensively characterized by powder X-ray diffraction, vibrational spectroscopy, and X-ray absorption spectroscopy. At ambient conditions solid solutions up to x = 0.75 crystallize in the monazite structure, whereas TbPO4 is isostructural to xenotime. For x = 0.8 a mixture of both polymorphs was obtained. Moreover, a phase with anhydrite structure was observed coexisting with xenotime, which was formed due to mechanical stress. Selected solid solutions were investigated at pressures up to ∼40 GPa using in situ high pressure synchrotron X-ray diffraction and in situ high pressure Raman spectroscopy. SmPO4 and Sm0.5Tb0.5PO4 monazites are (meta)stable up to the highest pressures studied here. TbPO4 xenotime was found to transform into the monazite structure at a pressure of about 10 GPa. The transformation of Sm0.2Tb0.8PO4 xenotime into the monazite polymorph commences already at about 3 GPa. This study describes the reversibility of the pressure-induced (Sm,Tb)PO4 xenotime-monazite transformation.

In situ Raman spectroscopy of pressure‐induced phase transformations in polycrystalline TbPO4, DyPO4, and GdxDy(1−x)PO4

AbstractXenotime DyPO4 and GdxDy(1−x)PO4 (x = 0.4, 0.5, 0.6) (tetragonal I41amd zircon structure) have been studied at ambient temperature under high pressures inside a diamond anvil cell with in situ Raman spectroscopy. The typical Raman‐active modes of the xenotime structure were observed at low pressures and the appearance of new Raman peaks at higher pressures indicated a phase transformation to a lower symmetry structure—likely monoclinic. Raman mode softening was observed, resulting in a line crossing at approximately 7‐8 GPa for each material and preceding the phase transformation. The onset of phase transformation for DyPO4 occurred at a pressure of 15.3 GPa. DyPO4 underwent a reversible phase transformation and returned to the xenotime phase after decompression. The transformation pressures of the solid solutions (GdxDy(1−x)PO4) were in the range 10‐12 GPa. The GdxDy(1−x)PO4 solid solutions yielded partially reversible phase transformations, retaining some of the high‐pressure phase spectrum while reforming xenotime peaks during decompression. The substitution of Gd into DyPO4 decreased the transformation pressure relative to pure DyPO4. The ability to modify the phase transformation pressures of xenotime rare‐earth orthophosphates by chemical variations of solid solutions may provide additional methods to improve the performance of ceramic matrix composites.

Synthesis and lithium-ion storage performances of LiFe0.5Co0.5PO4/C nanoplatelets and nanorods

Carbon-coated olivine-structured LiFe0.5Co0.5PO4 solid solution was synthesized by a facile rheological phase method and applied as cathode materials of lithium-ion batteries. The nanostructure’s properties, such as morphology, component, and crystal structure for the samples, characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer, Emmett, and Teller (BET) determination, X-ray photoelectron spectroscopy (XPS), and the electrochemical performances were evaluated using constant current charge/discharge tests and electrochemical impedance spectroscopy (EIS). The results indicate that nanoplatelet- and nanorod-structured LiFe0.5Co0.5PO4/C composites were separately obtained using stearic acid or polyethylene glycol 400 (PEG400) as carbon source, and the surfaces of particles for the two samples are ideally covered by full and uniform carbon layer, which is beneficial to improving the electrochemical behaviors. Electrochemical tests verify that the nanoplatelet LiFe0.5Co0.5PO4/C shows a better capacity capability, delivering a discharge specific capacity of 133.8, 112.1, 98.3, and 74.4 mAh g−1 at 0.1, 0.5, 1, and 5 C rate (1 C = 150 mA g−1); the corresponding cycle number is 5th, 11th, 15th, 20th, and 30th, respectively, whereas the nanorod one possesses more excellent cycling ability, with a discharge capacity of 83.3 mAh g−1 and capacity retention of 86.9% still maintained after cycling for 100 cycles at 0.5 C. Results from the present study demonstrate that the LiFe0.5Co0.5PO4 solid solution nanomaterials with favorable carbon coating effect combine the characteristics and advantage of LiFePO4 and LiCoPO4, thus displaying a tremendous potential as cathode of lithium-ion battery.

Rubidium-cation conductivity of Rb3–2x Pb x PO4 solid solutions

New Rb3PO4-based ceramic materials with high rubidium-cation conductivity in the Rb3–2x Pb x PO4 system have been synthesized and studied. Introduction of Pb2+ cations leads to a sharp increase in the conductivity of rubidium orthophosphate due to formation of cation vacancies and, at temperatures 350–550°C, also due to the stabilization of high-temperature cubic modification Rb3PO4. At high temperatures, the electrolytes prepared have very high ion conductivity higher than 10–1 S cm–1 at 700°C, which is higher than the values previously obtained in similar systems with additions of tin and cadmium ions. The factors influencing the transport properties of the materials under study are discussed.

Atomistic modeling and experimental studies of radiation damage in monazite-type LaPO4 ceramics

We simulated the threshold displacement energies (Ed), the related displacement and defect formation probabilities, and the energy barriers in LaPO4 monazite-type ceramics. The obtained Ed values for La, P, O primary knock-on atoms (PKA) are 56eV, 75eV and 8eV, respectively. We found that these energies can be correlated with the energy barriers that separate the defect from the initial states. The Ed values are about twice the values of energy barriers, which is explained through an efficient dissipation of the PKA kinetic energy in the considered system. The computed Ed were used in simulations of the extent of radiation damage in La0.2Gd0.8PO4 solid solution, investigated experimentally. We found that this lanthanide phosphate fully amorphises in the ion beam experiments for fluences higher than ∼1013ions/cm2.

Li Storage in Olivine Structure LiFexMn1-XPO4

LiMnPO4 shows higher specific energy than that of LiFePO4, but suffers from poor kinetics. The mixed-cation olivine material LiFexMn(1-x)PO4 combined the good rate capability of LiFePO4 and high potential of LiMnPO4. Commonly, LiFe0.5Mn0.5PO4 is considered to exhibit two pairs of plateau in charge-discharge curves associated with MnPO4/LiMnPO4 and FePO4/LiFePO4 phase transformation. We prepared carbon coated LiFe0.5Mn0.5PO4 solid solution material by solvothermal method. This material delivers typical two plateaus in charge/discharge curves at low current rate, but a third plateau appears only during discharge at relative high current rate. The discharge capacity in the addition medium plateau increases with the current rate increases. LiFe0.5Mn0.5PO4 discharge mainly proceeds via the medium plateau at high current rate. Electrochemical measurements demonstrate that the additional discharge plateau can still be attributed to Mn3+ reduction, but with a different mechanism than in pure LiMnPO4 due to the presence of Fe in LiMnPO4 framework that gives the conditions for better kinetics. Also the battery performance of a full battery consisting of LiFe0.2Mn0.8PO4 and layered transition-metal oxides (NMC) composite cathode and graphite anode was extensively studied. The addition of LMP in NMC greatly improved the battery safety.

Evidence for Lattice Strain and Non-ideal Behavior in the (La1−xEux)PO4 Solid Solution from X-ray Diffraction and Vibrational Spectroscopy

The monazite-type solid solution of LaPO$_4$ and EuPO$_4$ has been studied by X-ray diffraction, infrared (IR) and Raman spectroscopic techniques. A substantial excess molar volume has been derived from the X-ray data, and the Raman and IR spectra show band broadening typical for mixing of cations of different size on the cation sublattice. The IR spectra were interpreted by the autocorrelation method and the excess autocorrelation parameter $\Delta{corr}^{ex}$ shows clear deviation from ideal solution behaviour, similar to the observed broadening of the Raman bands. The results can be interpreted in terms of local lattice strains resulting from the ion size effects of substitution of La$^{3+}$ by Eu$^{3+}$, and correlate very well with calorimetric measurements of the excess enthalpy that was previously measured.

Schottky contribution to the heat capacity of monazite type (La, Pr)PO4 from low temperature calorimetry and fluorescence measurements

We show that the combination of fluorescence spectroscopy and low temperature heat capacity measurements of Pr-containing samples in the (La,Pr)PO4 solid solution series can be employed to strongly constrain the Stark energy levels of Pr3+ in monazite type structures. The resulting set of Stark energy levels for the 3H4 ground state of Pr3+ reproduces the low temperature Schottky anomaly of the heat capacity much more accurately than theoretical models published earlier. We also show that there is no excess heat capacity along the binary solid solution with respect to an interpolation between the two end members LaPO4 and PrPO4.

Preparation and characterization of cerium-gadolinium monazites as ceramics for the conditioning of minor actinides

Monazites are of considerable interest for immobilization of minor actinides. In this work, the Gd1-xCexPO4 (0 ≤ x ≤ 1) series is synthesized via conventional solid–state reaction using Ce as the surrogate for minor actinide americium (Am), with microstructure/phase structure characterized by XRD, HRTEM, μ-Raman, and SEM as well. The optimized temperature for preparation of monazite-type Gd0.4Ce0.6PO4 solid solution is more than 1300 °C. At 1400 °C, the GdPO4 ceramic is essentially monazite with little metastable xenotime phase. The metastable xenotime (GdPO4) to monazite transformation occurs during the immobilizing phase of Ce element. The formation of monazite-type Gd1-xCexPO4 solid solutions in the range 0.1 ≤ x ≤ 1 is confirmed by the Rietveld refinement and Raman spectra. The change of Ce content has no significant influence on the morphology of the monazite-type Gd1-xCexPO4 compounds.

Solvothermal Synthesis of LiMn1–xFexPO4Cathode Materials: A Study of Reaction Mechanisms by Time-Resolved in Situ Synchrotron X-ray Diffraction

We applied time-resolved in situ synchrotron X-ray diffraction (XRD) to study the reaction processes and pathways during the solvothermal synthesis of the olivine-structured LiFePO4, LiMnPO4, and LiFe0.4Mn0.6PO4 with ethylene glycol C2H6O2 (EG) as the solvent by following the evolution of the crystal structures of the Fe/Mn-containing phases. We identified a stable intermediate phase in the synthetic reaction process of LiFePO4, viz., a ferrous oxalate EG complex (FeC2O4·C2H6O2), and resolved its structure; thus, we established a two-step reaction mechanism involving dissolution–precipitation followed by interface-coupled dissolution–reprecipitation for the synthesis of LiFePO4. The synthetic reactions in an LiFe0.4Mn0.6PO4 solid solution also followed a two-step process via the formation of a metastable intermediate phase bearing a structural similarity to FeC2O4·C2H6O2 that, however, has a slightly larger unit-cell, indicating that the substitution of Fe by Mn occurred at the intermediate stage. In cont...

Characterization of the carbon-coated LiNi1−y Co y PO4 solid solution synthesized by a non-aqueous sol-gel route

Nanosize carbon-coated samples of the solid solution LiNi1−y Co y PO4 were prepared and investigated with respect to high-voltage cathode materials (4–5 V) for Li-ion batteries. For the syntheses, a modified non-aqueous sol-gel approach under argon atmosphere was applied. Crystal structure and morphology of the products were analyzed by X-ray powder diffraction, scanning electron microscopy, and Raman spectroscopy. Phase pure samples crystallize in the olivine-type structure with a linear relation between lattice parameters and chemical composition. The mean crystal size of the particles is smaller than 300 nm with increasing agglomeration towards samples with higher nickel content. Effects of the Ni/Co ratio on P-O and M-O bonds were explored by FTIR and UV/VIS measurements, too. Substitution of Ni by Co causes larger cell volumes, longer atomic distances, and weaker P-O and M-O bonds. Additional studies focus on the mechanism of formation of LiNiPO4 and the conditions for the formation of the phosphide by-products Ni3P and Ni12P5 by carbothermal reduction. The electrochemical properties of all compounds were investigated by galvanostatic charge/discharge measurements and differential capacity analysis. The small particles of the sol-gel process lead to a superior capacity in comparison to a common solid-state synthesis. Cyclability of the whole solid-solution is evaluated for the first time. For a Ni content of 33 %, the voltage is shifted to a higher level and a positive effect on capacity retention is observed.

Preparation and microwave dielectric properties of Li(Mg1–xCox)PO4 ceramics for low-temperature cofired ceramic applications

Li(Mg1–xCox)PO4 (x=0–0.09) ceramics were prepared by the conventional solid-state ceramic method. The formation of single-phase Li(Mg1–xCox)PO4 solid solutions is confirmed by the X-ray diffraction (XRD) patterns. Co2+ substitution for Mg2+ can lower the sintering temperature and enhance the Qf value of LiMgPO4 ceramics. The LiMg0.95Co0.05PO4 ceramic sintered at 875°C reaches a maximum relative density of 97.4% and shows the microwave dielectric properties of εr=6.97, Qf=111,200GHz, and τf=–53.8ppm/°C. The negative τf value can be tuned nearly to zero by adding TiO2. The LiMg0.95Co0.05PO4–TiO2 composite ceramic with 16.1wt% TiO2 sintered at 875°C for 2h shows a near-zero τf value of +0.8ppm/°C, together with an εr value of 9.97 and a Qf value of 58,200GHz. The composite ceramic does not react with the commonly used electrode material silver and is a promising candidate for low-temperature cofired ceramic applications.

Synthesis, phase structure and microstructure of monazite-type Ce1−xPrxPO4 solid solutions for immobilization of minor actinide neptunium

Praseodymium was used as the surrogate for trivalent minor actinide neptunium, and a complete series of pure monazite-type Ce1−xPrxPO4 (x=0–1) solid solutions were successfully prepared by the solid state reaction. The effects of calcining temperature, holding time and Pr content on the structure of Ce1−xPrxPO4 solid solutions were investigated. The results show that although Pr6O11 (Pr23+Pr44+O11) exists two stabilized oxidation states, there has been no tetravalent praseodymium phosphate during the synthesis process. The optimized temperature for the synthesis of Ce0.8Pr0.2PO4 solid solution is more than 1100°C, and a hypothetical reaction mechanism is also proposed. Besides, the crystalline grains coarsen as the increasing of holding time. The linear variation of unit cell parameters and a gradual hypsochromic shift in the Raman spectra are observed with the increase of Pr content, indicating that cerium is progressively replaced by praseodymium and Ce1−xPrxPO4 solid solutions were prepared.