Fabrications of Nb-doped TiO<Subscript>2</Subscript> (TNO) transparent conductive oxide polycrystalline films on glass substrates by sol–gel method

Anatase Ti_0.94Nb_0.06O₂ (TNO) films were fabricated on glass substrates by sol–gel method using a dip-coating technique. The annealing treatment was separated into two steps, first in air at 350–550 °C for 1 h and then in vacuum of 4.0 × 10⁻⁴ Pa at 550 °C for 1 h. The influence of vacuum annealing treatment to the electrical and optical properties was discussed. Especially, the role of air annealing treatment from 350 to 550 °C on the crystallization and the structure of the films was analyzed. It is proved that the films annealed at 550 °C in air and then 550 °C in vacuum exhibited the minimum resistivity of 19.3 Ω·cm and the average optical transmittance of about 75% in the visible range, indicating that the sol–gel method is a feasible and promising method to fabricate TNO films.     

Thermal study on electrospun polyvinylpyrrolidone/ammonium metatungstate nanofibers: optimising the annealing conditions for obtaining WO<Subscript>3</Subscript> nanofibers

This article demonstrates how important it is to find the optimal heating conditions when electrospun organic/inorganic composite fibers are annealed to get ceramic nanofibers in appropriate quality (crystal structure, composition, and morphology) and to avoid their disintegration. Polyvinylpyrrolidone [PVP, (C₆H₉NO) _n ] and ammonium metatungstate [AMT, (NH₄)₆[H₂W₁₂O₄₀]·nH₂O] nanofibers were prepared by electrospinning aqueous solutions of PVP and AMT. The as-spun fibers and their annealing were characterized by TG/DTA-MS, XRD, SEM, Raman, and FTIR measurements. The 400–600 nm thick and tens of micrometer long PVP/AMT fibers decomposed thermally in air in four steps, and pure monoclinic WO₃ nanofibers formed between 500 and 600 °C. When a too high heating rate and heating temperature (10 °C min⁻¹, 600 °C) were used, the WO₃ nanofibers completely disintegrated. At lower heating rate but too high temperature (1 °C min⁻¹, 600 °C), the fibers broke into rods. If the heating rate was adequate, but the annealing temperature was too low (1 °C min⁻¹, 500 °C), the nanofiber morphology was excellent, but the sample was less crystalline. When the optimal heating rate and temperature (1 °C min⁻¹, 550 °C) were applied, WO₃ nanofibers with excellent morphology (250 nm thick and tens of micrometer long nanofibers, which consisted of 20–80 nm particles) and crystallinity (monoclinic WO₃) were obtained. The FTIR and Raman measurements confirmed that with these heating parameters the organic matter was effectively removed from the nanofibers and monoclinic WO₃ was present in a highly crystalline and ordered form.     

Cu-particle-dispersed (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript> composite thin films derived from sol–gel processing

Sol–gel processing of Cu-particle-dispersed (K_0.5Na_0.5)NbO₃ (Cu/KNN) thin films was studied in an attempt to develop a method producing piezoelectric composite films with good mechanical performance. The Cu/KNN films were prepared via crystallization annealing at 650–750 °C for 1 min in air, followed by reduction annealing at 400–500 °C for 1–2 h in a 5% H₂ and 95% Ar gas mixture. The resultant composite films consisted of perovskite KNN, metallic Cu, and Cu₄O₃. This suggests that the decomposition of Cu sources takes two different ways in this study. The Cu/KNN composite films containing Cu₄O₃ phases were produced by the crystallization annealing at 700 °C for 1 min followed by the reduction annealing at 500 °C for 1 h. Surface morphology observations reveal that these films have dense KNN matrix with a grain size of ~200 nm and uniformly dispersed Cu or Cu₄O₃ particles with a size of <500 nm.     

Crystalline phase content and ionic conductivity correlation in LATP glass–ceramic

Li₂O–Al₂O₃–TiO₂–P₂O₅ (LATP) glass was fabricated by conventional melt quenching route. Glass transition temperature (T _g = 296 °C) and crystallization temperatures (T _C1,2) were obtained from thermal analysis. LATP glass was converted to glass–ceramic by heat treatment in the range 550–950 °C for 6 h. X-ray diffraction analysis revealed LiTi₂(PO₄)₃ as a major phase. Ionic conductivity increased monotonically with concentration, reaching a maximum of ~10⁻⁴ S/cm. AlPO₄ phase was detected in samples heat-treated above 850 °C. Its presence decreased the conductivity, suggesting LiTi₂(PO₄)₃ phase as main contributor to high ionic conductivity. NMR spectra confirmed the presence of mobile ⁷Li ions in the entire sample series and also gave some information on the structure and dynamics of conductivity.     

Sol–gel elaboration and structural investigations of Lu<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> planar waveguides

Europium actived Lu₂O₃ sol–gel transparent and crack free films were deposited by dipping on silica substrates. The film microstructure was studied by waveguide Raman spectroscopy (WRS) with annealing temperatures from 400 up to 1,000 °C and X-ray diffraction. The WRS results and TEM observations were correlated and showed that crystallization of the lutetium oxide phase into cubic phase occurs at 600 °C and is stable up to 1,000 °C, the crystallite size increasing between ±38 nm with annealing temperature ranging from 600 to 1,000 °C. Opto-geometrical parameters were determined by m-lines spectroscopy using four different wavelengths of laser sources in order to confirm the step-index profile of the as-prepared waveguides. The Eu³⁺ doped films heat-treated at 1,000 °C presented a constant thickness for the wavelengths 493, 543, 594 and 632.8 nm and a density of 8.4 g cm⁻³. High-resolution X-ray images were obtained.     

Thermal,XRD, and magnetization studies on ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript> and NiAl<Subscript>2</Subscript>O<Subscript>4</Subscript> spinels,synthesized by citrate precursor method and annealed at 450 and 650 °C

Two aluminate spinel materials (ZnAl₂O₄ and NiAl₂O₄) were synthesized by the citrate precursor method. The citrate precursors consisting of coprecipitated citrates of Zn²⁺ or Ni²⁺ and aluminum were first subjected to thermal analysis (TG-DSC) for determining the optimum temperature for annealing. Two step decomposition was observed incorporating dehydration and formation of the aluminate. The second step gives an endo peak (−2937 J/g) at 356 °C in the DSC curve of the coprecipitated nickel(II) citrate–aluminum citrate gel in O₂ atmosphere. Kinetic/mechanistic analysis of the TG data has also been carried out and values of E _a, ΔS ^#, ΔG ^#, and A were approximated. On the basis of the findings, 450 °C has been chosen for annealing of the gels. Annealing has also been done at 650 °C for 1 h in muffle furnace in an attempt to obtain nanometric particles of aluminates (MAl₂O₄) {M = Ni, Zn} and to find out their magnetic properties which could render them useful for chemical sensing applications, etc. The TG-DSC curves of various powders which were obtained on annealing at the two temperatures did exhibit thermal instability when carried out in N₂ atmosphere. NiAl₂O₄ and ZnAl₂O₄ spinels (particle size 17 and 34 nm, respectively) are obtained in pure crystalline phase at 650 °C. ZnAl₂O₄ prepared this way shows coercivity values of 470 and 58.37 G and NiAl₂O₄, 107 and 23.24 G when annealed at 450 and 650 °C, respectively. ZnAl₂O₄ prepared by a polymer precursor method and annealed at 1000 °C, has earlier been reported to have coercivity value of 469 G. Thus, the citrate precursor method is good for the synthesis of ZnAl₂O₄, producing single phase nanocrystalline powder of high quality and crystallinity. The value of magnetization was found to be small in the present case for the NiAl₂O₄ spinel obtained at 450 °C.     

Thermal,structural and magnetic studies on chromite spinel synthesized using citrate precursor method and annealed at 450 and 650 °C

Chromite Spinel materials were synthesized in this study by the citrate precursor method using four divalent cations (Ni²⁺, Co²⁺, Zn²⁺, and Cu²⁺). Citrate precursors consisting of mixed chromium citrates were first subjected to a thermogravimetric (TG) analysis for determining optimum temperatures for annealing. TG of coprecipitated chromium(III) citrate–zinc citrate gel has been carried out separately in N₂ and O₂ atmospheres. In both the cases, dehydration is followed by a four-step decomposition. The TG data were subjected to kinetic/mechanistic analysis, and the values of activation energy and Arrhenius factor were approximated. TG curves of various powders which were obtained on annealing at the two temperatures did exhibit thermal instability when carried out in N₂ atmosphere. A large coercivity of 2701.01 Oe was observed for NiCr₂O₄ at 650 °C. On the basis of the results, 450 °C has been chosen for annealing treatment of the four gels. The samples were accordingly annealed at two different temperatures (450 and 650 °C) in a muffle furnace for 1 h in each case. The annealed powders were characterized using X-ray diffraction (XRD), SEM, and vibrating sample magnetometer (VSM). The XRD patterns show that annealing of CuCr₂O₄, NiCr₂O₄, and CoCr₂O₄ at 450 °C yields very small crystallites with poor Bragg reflections, although ZnCr₂O₄ samples show better peaks in XRD data. Annealing at 650 °C resulted in particle size range of 8–89 nm in the four cases. In the case of ZnCr₂O₄, the particle size was 8 nm.     

Preparation and electrocatalytic performance of Fe–N–C for electroreduction of H2O2

Fe–N–C catalysts were prepared through metal-assisted polymerization method. Effects of carbon treatment, Fe loading, nitrogen source, and calcination temperature on the catalytic performance of the Fe–N–C for H₂O₂ electroreduction were measured by voltammetry and chronoamperometry. The Fe–N–C catalyst shows optimal performance when prepared with pretreated active carbon, 0.2 wt.% Fe, paranitroaniline (4-NA) and one-time calcination. The Fe–N–C catalyst displayed good performance and stability for electroreduction of H₂O₂ in alkaline solution. An Al–H₂O₂ semi-fuel cell was set up with Fe–N–C catalyst as cathode and Al as anode. The cell exhibits an open-circuit voltage of 1.3 V and its power density reached 51.4 mW cm⁻² at 65 mA cm⁻².     

Structure and multiferroic properties of Bi<Subscript>5</Subscript>FeTi<Subscript>3</Subscript>O<Subscript>15</Subscript> thin films prepared by the sol–gel method

The Bi₅FeTi₃O₁₅ (BFTO) films of layered structure have been fabricated on Pt/Ti/SiO₂/Si substrates by the sol–gel method. The thermal decomposition behaviors of precursor powder were examined using thermo-gravimetric and differential scanning calorimeters analysis. The optimal heat treatment process for BFTO films were determined to be low-temperature drying at 200 °C for 4 min and high-temperature drying at 350 °C for 5 min followed by annealing at 740 °C for 60 min, which led to the formation of compact films with uniform grains of ~300 nm. The structural, surface topography, ferroelectric and magnetic properties of the films were investigated. The remnant polarization (2P _r) of BFTO thin films under an applied electric field of ~550 kV/cm are determined to be 67.5 μC/cm² . Meanwhile, the weak ferromagnetic properties of the BFTO films were observed at room temperature.     

Solid state synthesis of CuFe2O4 from Cu(OH)2?·?CuCO3–4FeC2O4?·?2H2O mixtures: mechanism of reaction and thermal characterization of CuFe2O4

Copper Ferrite has been prepared by solid state synthesis of milled mixtures of copper basic carbonate [Cu(OH)₂ · CuCO₃] and iron (II) oxalate dihydrate [FeC₂O₄ · 2H₂O]. The reaction mechanism has been studied by simultaneous TG/DSC analysis: the different steps of the mass loss process have been individuated along with the relevant enthalpy terms starting from both physical and mechanically activated mixtures. CuFe₂O₄ has been synthesized by annealing the mechanically activated mixture at 750–800 °C while no pure CuFe₂O₄ is obtained by annealing the physical mixture at temperatures as high as 1100 °C. CuFe₂O₄ has been characterized as concerns the molar het capacity, the tetragonal–cubic transition enthalpy and the Curie point.     

Single-step sol-gel deposition and dielectric properties of 0.4 μm thick, (001) oriented Pb(Zr,Ti)O<Subscript>3</Subscript> thin films

Single-step sol–gel deposition was attempted for realizing submicron thick, (001) oriented Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films, using an alkoxide solution containing polyvinylpyrrolidone (PVP). A solution of molar composition, Pb(NO₃)₂:Zr(OC₃H₇ ⁿ)₄:Ti(OC₃H₇ ⁱ)₄:PVP:H₂O:CH₃COCH₂COCH₃:CH₃OC₂H₄OH:C₃H₇ ⁿOH = 1.1:0.53:0.47:0.5:5:0.5:22:0.98, was prepared as a coating solution. Gel films were prepared on Pt(111)/TiO₂/SiO₂/Si(100) substrates by spin-coating, and calcined at 350 °C and annealed at 650 °C either in an electric furnace or in a near-infrared (IR) furnace. When calcined in the near-IR furnace, the films became (001) oriented on annealing. When calcined in the electric furnace, on the other hand, the films became randomly oriented on annealing. These observations indicate that the heating the gel films from the substrate side in the calcination step at 350 °C induces crystallographic orientation in the annealing step at 650 °C. The effects of the heating methods on the thermal decomposition of the gel films, and the microstructure and dielectric properties of the fired films were studied. Finally 0.4 μm thick, (001) oriented PZT films could be successfully prepared by non-repetitive, single-step deposition. The oriented film thus obtained had the remnant polarization 2P _r of 39 μC/cm² and the dielectric constant ε′ of 960 ± 169.     

Low-temperature NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Selective Reduction by Hydrocarbons on H-Mordenite Catalysts in Dielectric Barrier Discharge Plasma

Toward achieving selective catalytic reduction of NO _x by hydrocarbons at low temperatures (especially lower than 200 °C), C₂H₂ selective reduction of NO _x was explored on H-mordenite (H-MOR) catalysts in dielectric barrier discharge (DBD) plasma. This work reported significant synergistic effects of DBD plasmas and H-MOR catalysts for C₂H₂ selective reduction of NO _x at low temperatures (100–200 °C ) and across a wide range of O₂ content (0–15%). At 100 °C, NO _x conversions were 3.3, 11.6 and 66.7% for the plasma alone, catalyst alone and in-plasma catalysis (IPC) cases (with a reactant gas mixture of 500 ppm NO, 500 ppm C₂H₂, 10% O₂ in N₂, GHSV = 12,000 h⁻¹ and input energy density of 125 J L ⁻¹), respectively. At 200 °C, NO _x conversions were 3.8, 54.0 and 91.4% for the above three cases, respectively. Also, strong signals of hydrogen cyanide (HCN) byproduct were observed in the catalyst alone system by an on-line mass spectrometer. By contrast, almost no HCN was detected in the IPC system.     

Synthesis and properties of Co–Pt alloy silica core-shell particles

This paper describes a method for fabrication of silica-coated Co–Pt alloy nanoparticles in a liquid phase process. The Co–Pt nanoparticles were prepared from CoCl₂ (4.2 × 10⁻⁵ M), H₂PtCl₆ (1.8 × 10⁻⁵ M), citric acid (4 × 10⁻⁴ M) and NaBH₄ (1.2 × 10⁻² M) with a Co:Pt mole ratio of 7:3. The silica coating was performed in water/ethanol solution with a silane coupling agent, 3-aminopropyltrimethoxysilane (8 × 10⁻⁵ M), and a silica source, tetraethoxyorthosilicate (7.2 × 10⁻⁴ M) in the presence of the Co–Pt nanoparticles. Observations with a transmittance electron microscope and a scanning transmission electron microscope revealed that the Co-rich and Pt-rich nanoparticles were coated with silica. According to X-ray diffraction measurements, core particles were crystallized to metallic Co crystallites and fcc Co–Pt alloy crystallites with annealing in air at 300–500 °C. Magnetic properties of the silica-coated particles were strongly dependent on annealing temperature. Maximum values of 11.4 emu/g-sample for saturation magnetization and 365 Oe for coercive field were obtained for the particles annealed at 300 and 500 °C, respectively. Annealing at a temperature as high as 700 °C destroyed the coating structures because of crystallization of silica shell, resulting in reduction in saturation magnetization and coercive field.     

Preparation of CuAlO<Subscript>2</Subscript> thin films with high transparency and low resistivity using sol–gel method

CuAlO₂ thin films were deposited on quartz substrates by sol–gel process using copper acetate monohydrate and aluminum nitrate nanohydrate as starting materials and isopropyl alcohol as solvent. The influence of annealing temperature on the film structure and the phase evolution of CuAlO₂ films were investigated, so as to obtain CuAlO₂ films with superior performance. The phase compositions of the films were dependent on the annealing temperature. The films annealed at temperatures below 400 °C were amorphous while those annealed above 400 °C were polycrystalline. The phases of CuO and CuAl₂O₄ appeared gradually with the increase of annealing temperature. When the heat treatment temperature was elevated to 900 °C, the uniform and dense films with single phase of CuAlO₂ were obtained, with a resistivity of 15 Ωcm. The transmittance of the 310 nm-thick CuAlO₂ film is 79% at 780 nm and the direct optical band gap is 3.43 eV.     

Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript>,Tb<Superscript>3+</Superscript> thin films prepared by sol–gel method: structural and optical studies

Y₂O₃: Eu³⁺,Tb³⁺ transparent, high density and optical quality thin films were prepared by the sol–gel dip-coating technique. Yttrium (III) 2,4-pentadionate was used as a precursor by its hydrolysis in ethanol. The doping agents were incorporated in the form of europium and terbium nitrate. Structural, morphological and optical properties of prepared films were investigated for different annealing temperatures in order to establish the ideal processing route that enhances the luminescent properties. X-ray diffraction (XRD) analysis shows the cubic phase for 10-layer films and annealing temperatures higher than 500°C. At 700°C, highly densified (4.52 g cm⁻³) and very smooth films (1.4 nm at 700°C) are produced, composed of crystallites with a grain size of 11 nm. The film thickness, refractive index and porosity, as well as the luminescent properties, were found to vary with treatment temperature.     

Infrared absorption spectra of Er3+-doped Al2O3 nanopowders by the sol-gel method

The Er³⁺-doped Al₂O₃ nanopowders have been prepared by the sol-gel method, using the aluminium isopropoxide [Al(OC₃H₇)₃]-derived γ-AlOOH sols with addition of the erbium nitrate [Er(NO₃)₃·5H₂O]. The five phases of γ-(Al,Er)₂O₃, θ-(Al,Er)₂O₃, α-(Al,Er)₂O₃, ErAlO₃, and Al₁₀Er₆O₂₄ were detected with the 0–20 mol% Er³⁺-doped Al₂O₃ nanopowders at the different sintering temperature of 600–1200°C. The average grain size was increased from about 5 to 62 nm for phase transformation of undoped γ-Al₂O₃→α-Al₂O₃ at the sintering temperature from 600 to 1200°C. At the same sintering temperature, average grain size was decreased with increase of the Er³⁺ doping concentration. Infrared absorption spectra of γ-Al₂O₃ and θ-Al₂O₃ nanopowders showed the two broad bands of 830–870 and 550–600 cm⁻¹, the three broad bands of 830–870, 750–760, and 550–600 cm⁻¹, respectively. The infrared absorption spectra for the α-Al₂O₃ nanopowder showed three characteristic bands, 640, 602, and 453 cm⁻¹. The two characteristic bands of 669 and 418 cm⁻¹ for Er₂O₃ clusters were observed for the Er³⁺-doped Al₂O₃ nanopowders when Er³⁺ doping concentration was increased up to 2 mol%. The 796, 788, 725, 692, 688, 669, 586, 509, 459, and 418 cm⁻¹ are the characteristic bands of Al₁₀Er₆O₂₄ phase.     

Low temperature preparation and electric properties of highly (100)-oriented Pb<Subscript>0.8</Subscript> La<Subscript>0.1</Subscript>Ca<Subscript>0.1</Subscript>Ti<Subscript>0.975</Subscript>O<Subscript>3</Subscript> thin films prepared by a sol–gel route

Highly (100)-oriented Pb_0.8La_0.1Ca_0.1Ti_0.975O₃ (PLCT) thin films deposited on Pt/Ti/SiO₂/Si substrate were successfully achieved by a sol–gel route. The influence of annealing temperature on microstructures and electric properties was investigated; it was found that the PLCT film could be crystallized only at 450 °C. When the annealing temperature increased to 500 °C, the PLCT film exhibited highly (100)-oriented, which also possessed higher remnant polarization Pr (27 μC/cm²) and better pyroelectric figure of merit (F _d = 205 μC/m²k) at room temperature. It was also found too high annealing temperature (625 °C) could lead to recrystallization of film, and the small grains caused by recrystallization could make polarization reversal difficult and disturbed the preferred crystal growth in film, which was not benefit to obtain enhanced electric properties.     

The microstructure and magnetic properties of Ni<Subscript>0.4</Subscript>Zn<Subscript>0.6</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> films prepared by spin-coating method

Nickel zinc ferrite (Ni_0.4Zn_0.6Fe₂O₄) films on Si (100) substrate were synthesized using a spin-coating method. The crystallinity of the Ni_0.4Zn_0.6Fe₂O₄ films with the thickness of about 386 nm became better as the annealing temperature increased. The films have smooth surface, relatively good packing density and uniform thickness. The volatilization of Zn is serious at 900 °C. With the increase of annealing temperature, the saturation magnetization M _s increases in the temperature ranging from 400 to 700 °C, however, decreases above 700 °C, and the coercivity H _c increases in the temperature range 400–800 °C, decreases above 800 °C. After annealed at 700 °C for 2 h in air with the heating rate 2 °C/min, the film shows a maximum saturation magnetization M _s of 349 emu/cc and low coercivity H _c of 66 Oe. The M _s is higher than others which prepared by this method, however, the H _c is lower. The M _s of Ni_0.4Zn_0.6Fe₂O₄ films annealed at 700 °C increases with increasing annealing time and the H _c changes slightly.     

Effect of annealing temperatures and of high content of the iron ion (Fe<Superscript>3+</Superscript>)-doping on transition anatase–rutile phase of nanocrystalline TiO<Subscript>2</Subscript> thin films prepared by sol–gel spin coating

Titanium dioxide doped with iron (III) was prepared by sol–gel Spin Coating method. The phase structures, morphologies, particle size of the doped TiO₂ have been characterized by X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM) and ultraviolet–visible (UV–Vis) spectrophotometer. The XRD and Raman results show that the 10% Fe³⁺-doped TiO₂ thin films crystallize in anatase phase between 600 and 800 °C, and into the anatase–rutile phase at 1,000 °C, and further into the rutile phase when the content of Fe³⁺ increases (20%). The grain size calculated from XRD patterns shows that the crystallinity of the obtained anatase particles increased from 39.4 to 43.4 nm as the temperature of annealing increase, whereas the size of rutile crystallites increases, with increasing Fe³⁺ concentrations from 36.9 to 38.1 nm. The AFM surface morphology results confirmed that the particle size increases by increasing the annealing temperature and also with an increasing of Fe³⁺ content. The optical band gap (E _g) of the films was determined by the UV–Vis spectrophotometer. We have found that the optical band gap decreased with an increasing of annealing temperatures and also with an increasing of Fe³⁺ content.     

Electrochemical characterization of praseodymium centers in Pr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> zirconias using electrocatalysis and photoelectrocatalysis

The voltammetry of nanoparticles and scanning electrochemical microscopy are applied to characterize praseodymium centers in tetragonal and monoclinic zirconias, doped with praseodymium ions (Pr _x Zr_1−x O₂), prepared via sol–gel routes. Doped zirconia nanoparticles were synthesized by a sol–gel liquid-phase route and characterized by different techniques, including X-ray diffraction powder pattern, ultraviolet–visible diffuse reflectance spectroscopy, infrared spectroscopy, and transmission electron microscopy (TEM). Gels annealed at around 400 °C yielded tetragonal Pr _x Zr_1−x O₂ phases. The monoclinic forms of Pr-doped ZrO₂ were obtained by annealing at temperatures higher than 1,100 °C. TEM micrographs proved that the size of the nanoparticles produced was dependent on their crystalline form, around 15 and 60 nm for tetragonal and monoclinic, respectively. The electrochemical study confirmed that a relatively high content of praseodymium cation was in the chemical state (IV), i.e., as Pr⁴⁺, in both zirconia host lattices. The catalytic and photocatalytic effects of Pr⁴⁺ centers located in the monoclinic zirconia lattice on nitrite reduction and oxygen evolution reaction were studied.