Mixed Oxide Films Research Articles

How to stabilize highly active Cu+ cations in a mixed-oxide catalyst

Mixed-metal oxides exhibit novel properties that are not present in their isolated constituent metal oxides and play a significant role in heterogeneous catalysis. In this study, a titanium-copper mixed-oxide (TiCuOx) film has been synthesized on Cu(111) and characterized by complementary experimental and theoretical methods. At sub-monolayer coverages of titanium, a Cu2O-like phase coexists with TiCuOx and TiOx domains. When the mixed-oxide surface is exposed at elevated temperatures (600–650K) to oxygen, the formation of a well-ordered TiCuOx film occurs. Stepwise oxidation of TiCuOx shows that the formation of the mixed-oxide is faster than that of pure Cu2O. As the Ti coverage increases, Ti-rich islands (TiOx) form. The adsorption of CO has been used to probe the exposed surface sites on the TiOx–CuOx system, indicating the existence of a new Cu+ adsorption site that is not present on Cu2O/Cu(111). Adsorption of CO on Cu+ sites of TiCuOx is thermally more stable than on Cu(111), Cu2O/Cu(111) or TiO2(110). The Cu+ sites in TiCuOx domains are stable under both reducing and oxidizing conditions whereas the Cu2O domains present on sub-monolayer loads of Ti can be reduced or oxidized under mild conditions. The results presented here demonstrate novel properties of TiCuOx films, which are not present on Cu(111), Cu2O/Cu(111), or TiO2(110), and highlight the importance of the preparation and characterization of well-defined mixed-metal oxides in order to understand fundamental processes that could guide the design of new materials.

Mg–Al mixed metal oxide film derived from layered double hydroxide precursor film: Fabrication and antibacterial properties

Mg–Al layered double hydroxide (LDH) precursor films are fabricated in situ by urea hydrolysis using pure Al as both the substrate and Al source. X-ray diffraction patterns and scanning electron microscopy images show that Mg–Al LDH films are fabricated in situ. After calcination at 500 °C for 4 h, Mg–Al mixed metal oxide (MMO) films that inherited the microstructure of LDH precursor films are obtained. The surface concentration of nano-MgO dispersed in the MMO matrix and the microstructure of the films may be tailored by varying the crystallization time of LDH precursor films. The superhydrophilic property of MMO films arising from their microstructure can reduce the adsorption and adhesion of bacteria and retard biofilm formation. Moreover, nano-MgO dispersed in the MMO matrix has high bactericidal activity against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Vibrio fischeri. Mg–Al MMO films obtained in the present work have excellent antibacterial activities that are due to synergistic effects and thus have potentially applications in antibacterial coatings.

Effects of Ni2+/3+ Redox Peak Potential on Oxygen Evolution Activity of Mixed-Transition-Metal-Oxides in Alkaline Electrolyte

High-performance, low-cost electrocatalysts for the oxygen evolution reaction (OER) in alkaline electrolytes are vital for the commercialization of water electrolysis systems. Modular water electrolyzers could be the building blocks of a “plug & play” hydrogen highway infrastructure which would allow on-demand hydrogen production for re-fueling fuel-cell electric vehicles. Current state-of-the-art water electrolysis systems are based on proton-exchange-membrane (PEM) technology. The highly acidic environment of these PEM systems requires the use of rare & expensive platinum group metals (PGMs). Recent break-throughs in anion-exchange-membrane (AEM) technology have re-ignited the development of non-PGM catalysts for operation in alkaline electrolytes.1 Recent literature has shown that PGM-free AEM-electolyzers can achieve performance on par with PEM systems.2 However the mass-loading of the catalysts in this proof-of-concept study was quite high. Further increases in HER & OER activity & stability will move these systems closer to commercial deployment. Recent studies have shown that Ni-Fe hydroxides exhibit the highest OER activity of any non-PGM electrocatalysts.3 Our research has investigated binary & ternary Ni-X-(Y) mixed metal oxides. Results indicate that amorphous (non-stoichiometric) oxy-hydroxide surfaces exhibit the greatest OER activity. Ni-Fe-Mo mixed oxide has shown OER activity on par with perovskites.4 We have identified that mixed metal oxide films exhibit shifts in the Ni2+/3+ redox peaks. In-situ XAS studies are correlated with CV data to show how mixing Ni-oxides with Co or Fe can stabilize or inhibit (respectively) formation of Ni in the 3+ oxidation state. These observations indicate that the OER enhancement from Ni-Fe-oxides is a result of charge-transfer from Fe to the Ni active sites, thus providing a lower (non-integer) Ni oxidation state. The resulting Nix+ (2<x<3) surface sites have been shown experimentally to form more amorphous surface structure5 and presumably behave as more reversible active sites. It is likely that the amorphous structure stabilizes the active oxy-hydroxide network, thus stabilizing the OER intermediates and decreasing the OER on-set potential. In addition, the more reversible Nix+ (2<x<3) active sites enable high turn-over-frequencies by decreasing the binding energy of the Ni-O2 adsreaction product. Acknowledgements: Authors acknowledge the financial support from Proton On-Site as part of an ARPA-E grant and use of the National Synchrotron Light Source (NSLS) (beamline X3B), Brookhaven National Lab (BNL).

Effects of Temperature on Niobium-Doped MgZnO Films Grown Using Radio-Frequency Magnetron Sputtering

Niobium-doped MgxZn1−xO (Nb-MZO) mixed oxide films with high transmittance were successfully deposited on sapphire substrates through radio-frequency (RF) magnetron sputtering using a 4-in ZnO/MgO/NbOx (75/20/5 wt%) target. In this study, the films were analyzed using Hall measurements, X-ray diffraction (XRD), transparent performance measurements, and X-ray photoelectron spectroscopy (XPS). XRD results showed two peaks: MgO2 (002)-wurtzite and MgxZn1−xO (111)-cubic peaks. The Nb-MZO films exhibited high transparency, with transmittance exceeding 90% in the visible region and a sharp absorption edge in the ultraviolet (UV) region, implying that the MgO content in the Nb-MZO layer increased the bandgaps. These results indicate that Nb-MZO films are ideal for use as transparent contact layers in near-UV light-emitting diodes. Hall measurements and XPS results successfully demonstrated the p-type conductivity of the Nb-MZO films because of the composition of the N-Nb binding caused by annealing in nitrogen atmosphere.

Lithium Electrochemical and Electrochromic Properties of Atmospheric Pressure Plasma Jet-Synthesized Tungsten/Molybdenum Mixed Oxide Films for Flexible Electrochromic Devices

Lithium electrochemical and electrochromic (EC) performances of flexible tungsten/molybdenum mixed oxide (WMo x O y C z ) films, deposited onto 40-Ω/square flexible polyethylene terephthalate/indium tin oxide substrates at room temperature (~23°C) and at the short exposed durations of 19-26 s using an atmospheric-pressure plasma-enhanced chemical vapor deposition with an atmospheric pressure plasma jet (APPJ) at various precursor injection angles, are investigated. The flexible organo-tungsten-molybdenum oxide (WMo x O y C z ) films have been identified for the remarkable EC performance for 200 cycles of reversible Li + ion intercalation and deintercalation in a 1-M LiClO 4 -propylene carbonate electrolyte by a potential sweep switching measurement between -1 and 1 V at a scan rate of 50 mV/s, even after being bent 360° around a 2.5-cm diameter rod for 1000 cycles. The optical modulation (AT) is up to of 75.6% at a wavelength of 691.9 nm for WMo x O y C z films cosynthesized with an APPJ.

Surface sites on Pt-CeO2 mixed oxide catalysts probed by CO adsorption: a synchrotron radiation photoelectron spectroscopy study.

By means of synchrotron radiation photoemission spectroscopy, we have investigated Pt-CeO2 mixed oxide films prepared on CeO2(111)/Cu(111). Using CO molecules as a probe, we associate the corresponding surface species with specific surface sites. This allows us to identify the changes in the composition and morphology of Pt-CeO2 mixed oxide films caused by annealing in an ultrahigh vacuum. Specifically, two peaks in C 1s spectra at 289.4 and 291.2 eV, associated with tridentate and bidentate carbonate species, are formed on the nanostructured stoichiometric CeO2 film. The peak at 290.5-291.0 eV in the C 1s spectra indicates the onset of restructuring, i.e. coarsening, of the Pt-CeO2 film. This peak is associated with a carbonate species formed near an oxygen vacancy. The onset of cerium oxide reduction is indicated by the peak at 287.8-288.0 eV associated with carbonite species formed near Ce(3+) cations. The development of surface species on the Pt-CeO2 mixed oxides suggests that restructuring of the films occurs above 300 K irrespective of Pt loadings. We do not find any adsorbed CO species associated with Pt(4+) or Pt(2+). The onset of Pt(2+) reduction is indicated by the peak at 286.9 eV in the C 1s spectra due to CO adsorption on metallic Pt particles. The thermal stability of Pt(2+) in Pt-CeO2 mixed oxide depends on Pt loading. We find excellent stability of Pt(2+) for 12% Pt content in the CeO2 film, whereas at a Pt concentration of 25% in the CeO2 film, a large fraction of the Pt(2+) is converted into metallic Pt particles above 300 K.

Gas sensing properties of the nanostructured anodic Zr–W oxide film

The sensing properties of nanostructured Zr–W mixed oxide film have been investigated. The film was prepared via anodizing a sputter-deposited Zr–W alloy layer through nanopores in an anodic alumina layer superimposed on the alloy. The morphology, structure and chemical composition of the film were examined by SEM and XRD. The film consists of an array of self-ordered nanocolumns protruding from a continuous thin oxide layer. The initially amorphous film material crystallizes to monoclinic WO3 and orthorhombic ZrO2 due to a high temperature annealing in air. A sensor employing the ZrO2–WO3 oxide film as active layer was fabricated and used for detecting various concentrations (1–1000ppm) of H2, CO, C2H5OH and NO2 at temperatures up to 300°C. In hydrogen detection experiments, the sensor was very fast, with a response time of 19s, and highly sensitive to hydrogen, with a response value of up to 50, while showing incomparably weaker and slower responses to carbon monoxide, ethanol and nitrogen dioxide. The features of the films revealed to date are of importance for improving the chemical, structural and exploitation stability of nanostructured tungsten-oxide-based films and their selectivity in hydrogen gas detection.

Nanostructured Cu-Zn Oxides for Photocathodic Water Splitting

In this study, we show that a metal alloy can be efficiently exploited, via controlled fabrication steps, to create mechanically robust and adherent, mixed metal oxide films with tunable photoelectrochemical (PEC) properties.Brass is an alloy of Cu and Zn and an inexpensive source of semiconducting Cu2O, CuO and ZnO, which have all been used separately as photocathodes or photoanodes respectively for solar water splitting. However, thermodynamics and free energy change predicts a prevalence of ZnO formation when brass is oxidized. In this work however, we co-fabricate Cu and Zn oxides to form a highly adherent, mixed metal oxide surface and investigate the relationship between structure, property and performance in a PEC cell.In order to make photocathodes, we first vacuum anneal brass which leads to a Zn-depleted Cu-rich surface. Following this, the foil is oxidized in air to obtain CuO. Simultaneously, Zn out-diffusion from the underlying brass, leads to formation of a mixed CuO-ZnO phase at the surface (Fig 1a) which is highly adherent to the metal foil underneath.Structural characterization of the oxide layer is undertaken using SEM, Raman, XPS and XRD. SEM shows the presence of CuO nanowires interspersed with ZnO fibers (Fig. 1b). Raman and XRD data confirm the presence of both CuO and ZnO phases on the surface (Fig. 1c,d). Current voltage characteristics in sodium sulphate solution shows robust photocathodic response (Fig. 1e).This study shows that thermal oxidation of metal alloys can lead to formation of highly interspersed, mixed oxide phases forming novel heterojunctions for use as economical and manufacturing-scalable energy harvesting devices.

Characterization of ZrO2 and (ZrO2)x(Al2O3)1−X thin films on Si substrates: effect of the Al2O3 component

ZrO2 and (ZrO2)x(Al2O3)1-x films were deposited by the sol-gel technique on Si substrates. The effect of the Al2O3 additive on the film surface morphology was studied by atomic force microscopy (AFM). The mixed oxide films showed a smoother morphology and lower values of the root-mean-square (RMS) roughness compared to ZrO2. Further, FTIR spectra indicated that ZrO2 underwent crystallization. The electrical measurements of the MIS structure revealed that the presence of Al2O3 and the amorphization affects its dielectric properties. The MIS structure with (ZrO2)x(Al2O3)1-x showed a lower fixed charge (~ 6×1010 cm−2) and an interface state density in the middle of the band gap of 6×1011 eV−1 cm−2). The dielectric constant measured was 22, with the leakage current density decreasing to 2×10−8 A cm−2 at 1×106 V cm−1.

Effect of alloying elements on the electrochemical behavior of Cu–Ni–Zn ternary system in sulfide-polluted saltwater

• Cu–Ni–Zn showed the lowest i corr in sulfide-polluted salt water. • XRD and XPS showed the formation of mixed oxy-hydroxide layer on the surface. • EIS showed Cu–Ni–Zn to have the highest semicircle diameter and phase maximum. • EFM confirmed the high resistance of Cu–Ni–Zn in sulfide-polluted media. • The existence of Ni and Zn improved the corrosion resistance of the alloy. Copper-based alloys suffer from accelerated corrosion in sulfide-polluted seawater. Herein, we investigated the effect of Ni and Zn as alloying elements on the electrochemical behavior of Cu in sulfide-polluted saltwater. Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) measurements have been performed to assess the effect of Ni and Zn. The Cu–Ni–Zn alloy showed the lowest corrosion current density ( i corr ) in the highest concentration of sulfide-polluted saltwater compared to the Cu, Cu–Ni and Cu–Zn counterparts. Morphological (SEM) and surface (XPS) analyses have been done to further understand the findings of electrochemical measurements. Thin films of mixed oxides (CuO and ZnO) and hydroxides (Cu(OH) 2 , Ni(OH) 2 and (Cu, Zn) 2 (OH) 3 Cl) were identified as the reason behind the observed resistivity of the ternary Cu–Ni–Zn alloy.

Stabilization of Catalytically Active Cu+ Surface Sites on Titanium–Copper Mixed‐Oxide Films

The oxidation of CO is the archetypal heterogeneous catalytic reaction and plays a central role in the advancement of fundamental studies, the control of automobile emissions, and industrial oxidation reactions. Copper-based catalysts were the first catalysts that were reported to enable the oxidation of CO at room temperature, but a lack of stability at the elevated reaction temperatures that are used in automobile catalytic converters, in particular the loss of the most reactive Cu(+) cations, leads to their deactivation. Using a combined experimental and theoretical approach, it is shown how the incorporation of titanium cations in a Cu2O film leads to the formation of a stable mixed-metal oxide with a Cu(+) terminated surface that is highly active for CO oxidation.

Model thin films of Ce(III)‐based mixed oxides

Ce(III) sites on cerium oxide‐based catalysts are known to be active in many reactions. In order to study the interaction of cerium dioxide with three easily oxidizable elements, aluminum, silicon, and tungsten, and to prepare multicomponent materials of the Ce(III) electronic structure, we followed two inverse approaches: we step‐wisely deposited (i) Al, Si, or W onto CeO2(111) and (ii) CeO2 onto Al(111), Si(111), or W(110). We found out that the interaction in all cases was very strong and lead to a formation of mixed oxides of CeAlO3, Ce4.67Si3O13, and Ce6WO12 composition determined by quantitative XPS. The elements were present in Ce(III), Al(III), Si(IV), and W(VI) oxidation states, and the maximum thickness of the films was limited as thicker overlayers prevent the diffusion of the element from the substrate. Above this limit, the deposited aluminum, silicon, or tungsten formed oxides of consequently lower oxidation states on the surface before their purely elemental form was growing, while in the inverse systems, the insufficient diffusion from the Al, Si, and W substrates caused the growth of CeO2 on top of the mixed oxide films. We show that this method permits to prepare model thin films of various thickness and finely tunable Ce(IV) contribution and position (below or above the mixed oxide). Copyright © 2014 John Wiley &amp; Sons, Ltd.

A Structured Catalyst toward Mercaptan Sweetening with Largely Enhanced Synergistic Effect

A structured catalyst has been fabricated by immobilizing cobalt phthalocyanine tetrasulfonate (CoPcS) on a MgNiAl mixed metal oxide (MgNiAl-MMO) film derived from calcination of layered double hydroxide (LDH). The resulting CoPcS/MgNiAl-MMO catalyst exhibits excellent activity, stability, and recyclability for the reaction of mercaptan sweetening. SEM images show that the structured catalyst is composed of thin MMO nanoflakes perpendicular to the Al substrate. The synergistic effect between the oxidation center (CoPcS) and the abundant moderate basic sites on the surface of the MgNiAl-MMO substrate plays an important role in the sweetening process, accounting for the largely enhanced catalytic behavior (conversion: 92.8%; selectivity: 100%). In addition, the structured catalyst exhibits superior catalysis regeneration performance, owing to its specific architecture and strong mechanical stability. This work demonstrates a facile approach for modulating the synergistic effect between the active center and...

Homomolecular non-coherent photon upconversion by triplet–triplet annihilation using a zinc porphyrin on wide bandgap semiconductors

Non-coherent upconversion, realized by homomolecular triplet–triplet annihilation of a zinc metalloporphyrin absorber, has been measured for the metalloporphyrin adsorbed on metal oxide films (ZrO2, TiO2 and ZrO2/TiO2 mixed oxides) in which the semiconductor conduction band energy lies between the metalloporphyrin’s upconverted and prompt S1 excited states. Upconverted emission was observed for pure and mixed metal oxide films, regardless of the relative energies of the states, indicating electron transfer from upconverted states to the semiconductor was not competitive. Upconversion was attributed to aggregation of the absorber, likely in defects on the films, leading to efficient homomolecular triplet–triplet annihilation.

Cupric Oxide-based p-type Transparent Conductors

This study examines the impact of doping on the resistivity of sputtered cupric oxide (CuO), and investigates the effects of co-sputtering CuO with tin dioxide (SnO2). It was found that films sputtered from a 2 at. % sodium-doped target have resistivities of four orders of magnitude lower than equivalent undoped films. Addition of oxygen was found to reduce the resistivity further. The best films were found to have resistivities of 4.3x10-2Ω.cm. Co-sputtering with SnO2 was found to increase the band gap significantly, although it also caused an increase in the resistivity. All mixed oxide films were both amorphous and p-type.

Hydrogen activation on Pt-Sn nanoalloys supported on mixed Sn-Ce oxide films.

We have studied the interaction of H2 with Pt-Sn nanoalloys supported on Sn-Ce mixed oxide films of different composition by means of synchrotron radiation photoelectron spectroscopy and resonant photoemission spectroscopy. The model catalysts are prepared in a three step procedure that involves (i) the preparation of well-ordered CeO2(111) films on Cu(111) followed by subsequent physical vapor deposition of (ii) metallic Sn and (iii) metallic Pt. The formation of mixed Sn-Ce oxide is accompanied by partial reduction of Ce(4+) cations to Ce(3+). Pt deposition leads to the formation of Pt-Sn nanoalloys accompanied by the partial re-oxidation of Ce(3+) to Ce(4+). Subsequent annealing promotes further Pt-Sn alloy formation at expense of the Sn content in the Sn-Ce mixed oxide. Adsorption of H2 on Pt-Sn/Sn-Ce-O at 150 K followed by stepwise annealing results in reversible reduction of Ce cations caused by spillover of dissociated hydrogen between 150 and 300 K. Above 500 K, annealing of Pt-Sn/Sn-Ce-O in a hydrogen atmosphere results in irreversible reduction of Ce cations. This reduction is caused by the reaction of hydrogen with oxygen provided by the mixed oxide substrate via the reverse spillover to Pt-Sn nanoalloy. The extent of the hydrogen and oxygen spillover strongly depends on the amount of Sn in the Sn-Ce mixed-oxide. We observe an enhancement of hydrogen spillover on Pt-Sn/Sn-Ce-O at low Sn concentration as compared to Sn-free Pt/CeO2. Although the extent of hydrogen spillover on Pt-Sn/Sn-Ce-O with high Sn concentration is comparable to Pt/CeO2, the reverse oxygen spillover is substantially suppressed on these samples.

Properties of V–Ce mixed-oxide thin films deposited by RF magnetron sputtering

Abstract Thin films of vanadium cerium mixed oxides are good counter-electrodes for electrochromic devices because of their passive optical behavior and very good charge capacity. We deposited thin films of V–Ce mixed oxides on glass substrates by RF magnetron sputtering under argon at room temperature using different power settings. The targets were pressed into pellets of a powder mixture of V2O5 and CeO2 at molar ratios of 2:1, 1:1, and 1:2. For a molar ratio of 2:1, the resulting crystalline film comprised an orthorhombic CeVO3 phase and the average grain size was 89 nm. For molar ratios of 1:1 and 1:2, the resulting films were completely amorphous in nature. Scanning electron microscopy images and energy-dispersive X-ray spectroscopy data confirmed these results. The optical properties of the films were studied using UV-Vis-NIR spectrophotometry. The transmittance and indirect allowed bandgap for the films increased with the RF power, corresponding to a blue shift of the UV cutoff. The average transmittance increased from 60.9% to 85.3% as the amount of CeO2 in the target material increased. The optical bandgap also increased from 1.94 to 2.34 eV with increasing CeO2 content for films prepared at 200 W. Photoacoustic amplitude (PA) spectra were recorded in the range 300–1000 nm. The optical bandgap was calculated from wavelength-dependent normalized PA data and values were in good agreement with those obtained from UV-Vis-NIR data. The thermal diffusivity calculated for the films increased with deposition power. For thin films deposited at 200 W, values of 53.556×10−8, 1.069×10−8, and 0.2198×10−8 m2/s were obtained for 2:1, 1:1, and 1:2 V2O5/CeO2, respectively.

Growth of Ti–O–Si mixed oxides by reactive ion-beam mixing of Ti/Si interfaces

Ti–O–Si mixed oxide films have been grown by reactive ion-beam mixing of Ti/Si interfaces using low energy (3 keV) ions. Shifts in the Ti 2p, Si 2p and O 1s x-ray photoelectron spectroscopy (XPS) bands are observed during bombardment revealing a different formation of chemical species to those of the pure Ti or Si oxides which have been attributed to the growth of a Ti–O–Si mixed oxide at the interface where Ti coordination is different to that of Ti in TiO2. Ultraviolet photoelectron spectroscopy measurements also show a shift of the valence band (VB) edge from 3 to 6 eV which support the change in the Ti local coordination from octahedral to tetrahedral with increasing fluence during bombardment. Angle resolved XPS results show that the in-depth distribution of species is consistent with the formation of a SiO2 outer layer followed by a layer of Ti–O–Si mixed oxide and a third layer of TiO2 when going from the outer surface to the substrate. This complex layer can be specifically attributed to the chemical reaction and the atomic mixing taking place during the interface bombardment with . The apparition of species related to Si on the external surface has been qualitatively explained using the existing cascade mixing models.

Mechanical assessment of suspended ALD thin films by bulge and shaft-loading techniques

We assessed mechanical properties of free-standing atomic-layer-deposited (ALD) Al2O3 thin films, mixed oxide (AlxTiyOz) films and Al2O3/TiO2 nanolaminates (75 and 200nm). Using bulge and microelectromechanical system shaft-loading techniques, we evaluated the Young’s modulus, residual stress and ultimate tensile stress of these films and laminates. Fits to the load–displacement curves provided estimates for the residual stress and Young’s modulus. We extracted a residual stress of 347–403MPa for Al2O3, 365–389MPa for AlxTiyOz and 450–455MPa for the nanolaminate. The Young’s modulus was 164–165GPa for Al2O3, 151–154GPa for mixed oxide and 148–169GPa for the nanolaminate. Thin membranes exhibited an ultimate tensile strength of 1.57–2.56GPa for Al2O3, 1.17–2.09GPa for AlxTiyOz and 1.23–2.26GPa for the nanolaminate. The ability to make thin, yet mechanically strong, suspended membranes is useful in micro- and nanosystem applications ranging from thermally insulated devices to large stroke mechanical actuators.

Optical properties of ceria–zirconia epitaxial films grown from chemical solutions

Epitaxial thin films of ceria–zirconia solid solutions were grown on yttria-stabilized zirconia (YSZ) substrates by chemical solution deposition. Characterization by X-ray diffraction, atomic force microscopy and variable angle spectroscopic ellipsometry show that high-quality, epitaxial, high density films, with a thickness in the range of 20–27 nm were obtained. Compositional dependence of the film optical constants (n and k) was determined from ellipsometry measurements. It was found that the optical properties for the mixed-oxide films smoothly vary between the values for the pure oxides and are best described by means of a Tauc–Lorentz (TL) model. Moreover, we found that the parameters of the TL model have a linear dependence on the cerium concentration. The obtained results can serve as a database for the thickness, composition and porosity characterization of CexZr1−xO2 thin films.