Hexagonal La2O3 Research Articles

Ball Milling of La2O3 Tailors the Crystal Structure, Reactive Oxygen Species, and Free Radical and Non-Free Radical Photocatalytic Pathways.

Non-free radical photocatalysis with metal oxide catalysts is an important advanced oxidation process that enables the removal of various emerging environmental pollutants, such as tetracycline. Here, four hexagonal La2O3 photocatalysts with different densities of oxygen vacancy and crystalline features are synthesized and then further treated by ball milling. Ball milling of these La2O3 photocatalysts is found to increase the amount of oxygen vacancies on their surfaces and thereby the amount of 1O2 species produced by them. The photocatalytic degradation of TC by these La2O3 photocatalysts depends on the oxygen vacancies present on them. Furthermore, the ones with a strong (101) diffraction peak remove tetracycline from water systems largely with 1O2 and •OH species, whereas those with a weak (101) diffraction peak do so mainly via 1O2 and direct electron transfer (DET) process. Their overall catalytic properties are also studied by density functional theory calculations. Moreover, the organic products produced from tetracycline by La2O3 photocatalysts containing a strong (101) diffraction peak are found to be less toxic than those produced by La2O3 photocatalysts containing a weak (101) diffraction peak. This study also provides convincing evidence that the structures of La2O3 determine the species that is produced by it and that end up mediating photocatalytic reaction pathways (i.e., free radical versus non-free radical) to degrade an emerging environment pollutant.

Investigating the physical and electrical properties of La2O3 via annealing of La(OH)3

A simple technique was utilized to fabricate pure hexagonal La2O3 nanorods by utilizing lanthanum(III) nitrate hexahydrate (La(NO3)3·6H2O) and ammonia (NH4OH). The La2O3 nanoparticles were analyzed using XRD, TGA, Raman, SEM, FTIR, TEM, PL spectroscopy, and Mott–Schottky techniques. The XRD analysis confirmed the production of La(OH)3 nanorods under appropriate conditions, which were then successfully converted into La2O2CO3 and finally into La2O3 nanorods through annealing. The TGA analysis showed that the total weight loss was due to water evaporation and the dissolution of minimal moisture present in the environment. The FTIR analysis confirmed the presence of functional groups. The SEM analysis revealed changes in morphology. The TEM analysis to determine the particle size. The PL findings showed three emission peaks at 390, 520, and 698 nm due to interband transitions and defects in the samples. The Mott–Schottky analysis demonstrated that the flatband potential and acceptor density varied with annealing temperature, ranging from 1 to 1.2 V and 2 × 1018 to 1.4 × 1019 cm−3, respectively. Annealing at 1000 °C resulted in the lowest resistance to charge transfer (Rct).

Effect of hydrostatic pressure on electronic, elastic, and optical properties of hexagonal lanthanum oxide (La2O3): A first principles calculations

Using DFT with PBE-GGA as the exchange correlation functional, the structural, electronic, optical, and elastic aspects of hexagonal lanthanum oxide (La2O3) were studied at different pressures. To accurately predict the results of an investigation of a material, several nuclear systems at the quantum scale must be calculated, along with enormous simulations. La2O3 is compressible at high pressure, according to our results, even though it retains its hexagonal phase even between 0 and 100GPa. La2O3 demonstrates mechanical stability under any external pressure that is applied. Applying external pressure in the range of 0 to 100GPa causes the bandgap to narrow. Next, La2O3’s optical response has been studied utilizing the dielectric function, refractive index, optical reflectivity, absorption coefficient, optical conductivity, and loss function up to 50eV. According to the research, hexagonal La2O3 may be suitable to use in optoelectronic and renewable energy systems.

Amorphous to Polycrystalline Phase Transition in La2O3 Films Grown on a Silicon Substrate Forming Si‐Doped La2O3 Films

Herein, La2O3 films are fabricated on a Si substrate without a La–Sr intermixing layer at the La2O3/Si interface using a pulsed laser deposition method. X‐ray diffraction data shows only two discernible peaks of the La2O3 films: hexagonal La2O3 (10‐1) and cubic La2O3 (222), indicating polycrystalline character. During film growth, the reflection high‐energy electron diffraction pattern from the La2O3 surface changes from an initial column shape to a complicated distributed dot pattern with narrow lines, suggesting possible structural property changes in the La2O3 film. The occurrence of a structural transition is confirmed by high‐resolution transmission electron microscopy (HRTEM), which exhibits a clear crystalline phase change from an initial ≈10 nm thick amorphous La2O3 film to polycrystalline La2O3 film on Si. Rutherford backscattering shows a reduced La–Si intermixing between La2O3 and Si. Furthermore, the results of X‐ray photoelectron spectroscopy atomic depth profile analysis show that observation of La‐silicate over the whole La2O3 film indicates that Si diffuses through whole thick La2O3 films forming Si‐doped La2O3 films. This study of the well‐defined structural characteristics and sharp interface of La2O3/Si will enable further understanding of high dielectric constant materials grown on Si by the introduction of advanced film growth technique.

Influence of NiO and La2O3 nanoparticles on the optical, mechanical and electrical properties of PVAc–PMMA blend: a comparative study

Nano-sized metal oxides are fascinating materials as fillers used for improving the polymeric materials’ performance and expanding their multifunctionality. Two metal oxides; NiO and La2O3 nanoparticles (NP) were prepared and introduced into poly(vinyl acetate)/poly(methyl methacrylate), PVAc/PMMA blend via solution casting route. XRD and HR-TEM analysis confirmed the preparation of a cubic NiO and a hexagonal La2O3 NP with an average crystallite size of 59.85 and 29.13 nm, respectively. Introducing NiO and La2O3 increases the films’ amorphous structure. FTIR analysis confirmed the existence of all blend’ functional groups and hydrogen bond formation. SEM investigation showed that NiO or La2O3 loading affects the blend surface morphology. A UV–vis-NIR study showed that NiO narrowed the direct bandgap of the blend from 4.1 to 3.3 eV, whereas La2O3 reduced it to 3.4 eV. 1.0 wt% NiO significantly improved the various optical constants of the blend. DMA revealed that storage modulus G′ increased with loading of 1 wt% NiO or La2O3 by 79.3% and 51.0%, respectively while G′ decreased with heating. The dielectric behavior of films is analyzed using several dielectric parameters. The maximum σ ac reported for 1.0 wt% NiO/blend film is 5.8 × 10−6 (S/cm). The AC conduction mechanism is discussed for all films in the temperature and frequency ranges (298−373 K) and (5 Hz−2 MHz). 1.0 wt%/PVAc/PMMA nanocomposite showed enhanced optical and mechanical properties, making it suitable for architectural, flexible display screens, and photovoltaic cell devices. Moreover, loading NiO and La2O3 improved the dielectric properties of the blend to be used in the semiconductor industry, besides energy storage devices and supercapacitors.

Phase equilibria in the La2O3-Y2O3-Gd2O3 system at 1500°C

The phase equilibria in the ternary La2O3-Y2O3-Gd2O3 system at 1500?C were studied by X-ray diffraction, petrography and electron microscopy in the overall concentration range. The samples of different compositions have been prepared from nitrate acid solutions by evaporation, drying and calcination at 1100 and 1500?C. The solid solutions based on various polymorphous forms of constituent phases and ordered phase of LaYO3 were revealed in the system. The isothermal section of the phase diagram for the La2O3-Y2O3-Gd2O3 system has been developed. It was established that in the ternary La2O3-Y2O3-Gd2O3 system fields of solid solutions exist based on hexagonal (A) La2O3 phase, monoclinic (B) modifications of La2O3 and Gd2O3, cubic (C) modification of Y2O3, as well as perovskite-type structure of LaYO3 (R) with rhombic distortions. The systematic study that covered the whole compositional range excluded the formation of new phases. The refined lattice parameters of the unit cell and the boundaries of the homogeneity fields for solid solutions were determined.

Surface properties of nano mesoporous lanthanum oxide synthesized by sol-gel method

This study investigates surface properties like surface acidity/basicity, surface reducibility, surface area, and porosity of nano mesoporous lanthanum oxide (La2O3) synthesized by the sol–gel method. X-ray diffraction (XRD) analysis confirms the formation of nanocrystalline hexagonal La2O3 at 800 °C. Fourier transform infrared spectra (FT-IR) shows the peaks corresponding to surface carbonate and surface water on La2O3. Morphology of La2O3 was studied by transmission electron microscopy (TEM). The surface acidity of La2O3 was measured by temperature-programmed desorption (TPD-NH3) analysis and surface basicity by TPD-CO2. TPD profiles show the presence of medium and strong acidic and basic sites on the surface of La2O3. La2O3 has more surface acidity compared to surface basicity. Temperature programmed reduction (H2-TPR) analysis indicates good stability of La2O3 towards reduction. The values of H2 consumption indicate a greater amount of reducible species on the surface. Surface area and porosity measurements were done using Braunauer-Emmet-Teller (BET) analysis. The pore size distribution curve is also determined from the Barrett-Joyner-Halenda (BJH) adsorption/ desorption isotherm. La2O3 is found to be mesoporous with pore diameter of 20.6 nm and has wide pore size distribution between 5 and 50 nm. Typical type IV isotherm with H3 type hysteresis loops at a high P/P0 value is observed for La2O3.

The 1S0 → 3P1 transition position shift of Bi3+ ion doped Ln2O3 (Ln = Lu, Gd, La) phosphors

A series of Bi3+ ion doped Ln2O3 (Ln = Lu, Gd, La) phosphors have been prepared through a simple urea-based precipitation method. The 1S0 → 3P1 transition position shift of Bi3+ ion has been investigated in Bi3+-doped Ln2O3 phosphors. This is caused by difference of covalency and coordination number. The 1S0 → 3P1 transition of Bi3+ ion in Gd2O3 crystal shifts to lower energy position than that in Lu2O3 crystal for the same site due to the larger radius of Gd3+ ion compared to Lu3+ ion. However, the 1S0 → 3P1 transition of Bi3+ ion shifts to higher energy position owing to the increase of coordination number from cubic phase Lu2O3 and Gd2O3 crystals to hexagonal phase La2O3 crystal. Our work provides a reference to achieve various photoluminesence performances of Bi3+ ion doped oxides.

Steering the Methane Dry Reforming Reactivity of Ni/La2O3 Catalysts by Controlled In Situ Decomposition of Doped La2NiO4 Precursor Structures.

The influence of A- and/or B-site doping of Ruddlesden–Popper perovskite materials on the crystal structure, stability, and dry reforming of methane (DRM) reactivity of specific A2BO4 phases (A = La, Ba; B = Cu, Ni) has been evaluated by a combination of catalytic experiments, in situ X-ray diffraction, X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and aberration-corrected electron microscopy. At room temperature, B-site doping of La2NiO4 with Cu stabilizes the orthorhombic structure (Fmmm) of the perovskite, while A-site doping with Ba yields a tetragonal space group (I4/mmm). We observed the orthorhombic-to-tetragonal transformation above 170 °C for La2Ni0.9Cu0.1O4 and La2Ni0.8Cu0.2O4, slightly higher than for undoped La2NiO4. Loss of oxygen in interstitial sites of the tetragonal structure causes further structure transformations for all samples before decomposition in the temperature range of 400 °C–600 °C. Controlled in situ decomposition of the parent or A/B-site doped perovskite structures in a DRM mixture (CH4:CO2 = 1:1) in all cases yields an active phase consisting of exsolved nanocrystalline metallic Ni particles in contact with hexagonal La2O3 and a mixture of (oxy)carbonate phases (hexagonal and monoclinic La2O2CO3, BaCO3). Differences in the catalytic activity evolve because of (i) the in situ formation of Ni–Cu alloy phases (in a composition of >7:1 = Ni:Cu) for La2Ni0.9Cu0.1O4, La2Ni0.8Cu0.2O4, and La1.8Ba0.2Ni0.9Cu0.1O4, (ii) the resulting Ni particle size and amount of exsolved Ni, and (iii) the inherently different reactivity of the present (oxy)carbonate species. Based on the onset temperature of catalytic DRM activity, the latter decreases in the order of La2Ni0.9Cu0.1O4 ∼ La2Ni0.8Cu0.2O4 ≥ La1.8Ba0.2Ni0.9Cu0.1O4 > La2NiO4 > La1.8Ba0.2NiO4. Simple A-site doped La1.8Ba0.2NiO4 is essentially DRM inactive. The Ni particle size can be efficiently influenced by introducing Ba into the A site of the respective Ruddlesden–Popper structures, allowing us to control the Ni particle size between 10 nm and 30 nm both for simple B-site and A-site doped structures. Hence, it is possible to steer both the extent of the metal-oxide-(oxy)carbonate interface and its chemical composition and reactivity. Counteracting the limitation of the larger Ni particle size, the activity can, however, be improved by additional Cu-doping on the B-site, enhancing the carbon reactivity. Exemplified for the La2NiO4 based systems, we show how the delicate antagonistic balance of doping with Cu (rendering the La2NiO4 structure less stable and suppressing coking by efficiently removing surface carbon) and Ba (rendering the La2NiO4 structure more stable and forming unreactive surface or interfacial carbonates) can be used to tailor prospective DRM-active catalysts.

STRUCTURE OF ISOTHERMAL SECTIONS OF THE DIAGRAM OF THE STATE OF THE SYSTEM ZrO2 – La2O3 – Eu2O3 AT TEMPERATURES 1500 AND 1250 °C

Using the methods of X-ray phase and microstructural analyzes, phase equilibria and structural transformations in the ZrO2 – La2O3 – Eu2O3 system at temperatures of 1500 and 1250 ºC in the whole range of concentrations were studied. Based on the obtained data, the corresponding isothermal cross sections are constructed. It is established that the fields of solid solutions are formed in the system on the basis of cubic (F) modification with fluorite type structure, tetragonal (T) modification ZrO2, monoclinic (B) and cubic (C) modifications Eu2O3, hexagonal (A) modification La2O3, as well as ordered phases with a structure of the pyrochlor type Ln2Zr2O7 (Py). The boundaries of the phase fields and the parameters of the unit cells of the formed phases are determined. It was found that in the region with a high content of ZrO2 solid solutions are formed on the basis of tetragonal modification of ZrO2. The solubility of La2O3 in T-ZrO2is small and is ∼ 0.5% (mol.), which is confirmed by X-ray phase analysis and microstructural studies. It is established that at 1500 and 1250°C a continuous series of solid solutions is formed on the basis of an ordered phase of pyrochlor (Py) type Ln2Zr2O7. With decreasing temperature, the region of homogeneity of the specified solid solution narrows. Isothermal cross sections of the state diagram of the ZrO2-La2O3-Eu2O3 system at 1500 and 1250°C have a similar structure, although they are characterized by some differences due to the structure of the limiting binary systems. No new phases in the ternary system ZrO2 – La2O3 – Eu2O3 were detected at the studied temperatures.

Eco-friendly synthesis of lanthanum oxide nanoparticles by Eucalyptus globulus leaf extracts for effective biomedical applications

The development of nanoparticles (NPs) for biomedical and pharmaceutical applications is in high demand in the field of science and technology, due to their potential inhibition against pathogens. The eco-friendly green methodology is used for the synthesis of lanthanum oxide (La2O3) Nps using Eucalyptus globulus (E. globulus) leaf extracts. X-ray diffraction analysis (XRD) and selected area electron diffraction (SAED) studies reveal the formation of hexagonal structured La2O3 NPs. The vibrational modes of La2O3 were analyzed using Fourier transform infrared (FTIR) analysis. The Ultraviolet–visible (UV–Vis) analysis revealed the optical absorption of La2O3 with a cutoff wavelength of 290 nm. The particle distribution and surface nature were confirmed by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM) analysis with an average particle size of 50.37 nm. The main aim of this study is to control various inflammations and diabetic diseases using La2O3 as a potential inhibiting drug.

Hexagonal La2O3 Nanocrystals Chemically Coupled with Nitrogen‐Doped Porous Carbon as Efficient Catalysts for the Oxygen Reduction Reaction

The construction of nano-scale hybrid materials with a smart interfacial structure, established by using rare earth oxides and carbon as building blocks, is essential for the development of economical and efficient catalysts for oxygen reduction reactions (ORRs). In this work, hexagonal La2 O3 nanocrystals on a nitrogen-doped porous carbon (NPC) derived from crop radish, served as building bricks, are prepared by chemical precipitation and then calcination at elevated temperatures. The obtained La2 O3 /NPC hybrid exhibits a very high ORR activity with a half-wave potential of 0.90 V, exceeding that of commercial Pt/C (0.83 V). Both DFT theoretical and experimental results have verified that the significantly enhanced catalytic performance is ascribed to the formation of the C-O-La covalent bonds between carbon and La2 O3 . Through the covalent bonds, electrons can transfer from the carbon to La2 O3 and occupy the unfilled eg orbital of the La2 O3 phase. This results in the accelerated adsorption of active oxygen and the facilitated desorption of the surface hydroxides (OHad - ), thereby promoting the ORR over the catalyst.

The accurate control of the La2O3 hierarchical structure of the flower-like microspheres accompanied with vertical-standing nanopetals and the electrowetting responses with low voltage actuation

A simple hydrothermal method is successfully used to prepare the La2O3 film, and the accurate control of its surface structure is realized through the hydrothermal temperature and time from the sparsely dispersed compact microspheres to closely packed microsphere film, then from the hierarchical structure of the sparsely dispersed compact and flower-like microspheres accompanied with the discrete vertical-standing nanopetals to the hierarchical structure constituted by the closely packed compact microspheres and dense vertical-standing nanopetals. The XRD analysis shows the prepared film is mainly made of hexagonal La2O3 accompanied with some impurities of La(OH)2NO3, La(OH)3 and La2TiO5. Valuably, the prepared La2O3 film has high capacitance which can be modulated by surface structure, and achieves the maximum when the surface structure is hierarchical structure constituted by the closely packed compact microspheres and vertical-standing nanopetals. Eventually, the high capacitance leads to the electrowetting-on-dielectric (EWOD) responses with low voltage actuation below 8 V and wide contact angle modulation range of about 131°. The works are very beneficial to the design and preparation of supercapacitor and EWOD devices with high performance.

Anomalous lattice compression in the hexagonal La2O3– A high pressure X-ray diffraction, Raman spectroscopy and first principle study

High pressure behavior of hexagonal rare earth sesquioxide La2O3 have been investigated using X-ray diffraction, Raman spectroscopy and first principle calculations. Though the hexagonal structure is stable up to 26.5 GPa, incompressibility along the a axis is visible above 9.7 GPa. Rietveld structure refinements in conjunction with the Stephans anisotropic strain broadening model revealed the onset of an atypical bond compression and modification in the relative intensities of the diffraction peaks at ∼5.6 GPa. A significant increase in the intensity of 100 reflection and a clear reduction in the intensity of 103 reflection above 5.6 GPa suggests that pressure induces sliding of the adjacent La–O layers in opposite directions rather than compressing along the a axis. Further, a negative correlation of in-plane strain with pressure above 5.6 GPa indicate the layer sliding is accompanied by a reduction of in-plane strain in the hexagonal structure. Raman studies show the lifting of the degeneracy of the two stretching modes, in-plane Eg and out of plane A1g, and the change of slope of ω vs. P curve for the two in-plane Eg modes at 3.6 GPa. First principle density functional theory calculation substantiates our experimental observations that the pressure induced anisotropic strain distribution is driving the system into low energy configurations. The Birch –Murnaghan equation of state fit to the experimental pressure-volume data yielded a bulk modulus value of B0 = 102(5) GPa with B′0 = 9.8(1.0) for P ≤ 9.7 GPa, in good agreement with the 114 GPa of density functional theory calculations.

Role of template layers for heteroepitaxial growth of lanthanum oxide on GaN(0001) via atomic layer deposition

La2O3 has been reported as a good gate dielectric for GaN-based high electron mobility transistor and metal-oxide-semiconductor field effect transistor applications. In this study, atomic layer deposition (ALD) was selected as the deposition technique, and the growth behavior and structure of La2O3 films on GaN(0001) were investigated. Unlike La2O3 deposited by molecular beam epitaxy (MBE) at 450 °C that can form a two-dimensional film directly on GaN(0001), island growth mode was observed when a La2O3 film was deposited directly on GaN(0001) at 250 °C by ALD using tris(N,N′-diisopropylformamidinato)-lanthanum as the precursor and H2O as the coreactant. Only with the use of a template layer, a 2 nm-thick hexagonal La2O3 film deposited by MBE or a 3 nm-thick cubic Er2O3 film deposited by ALD, can a two-dimensional crystalline ALD-La2O3 thin film be formed on GaN(0001). Reflection high-energy electron diffraction, x-ray diffraction, and scanning transmission electron microscopy were conducted to verify the films’ crystalline nature and structure. The ALD-La2O3 film retains a cubic structure on ALD-Er2O3 templated-GaN(0001), while it transforms from the cubic phase to a mix of cubic and hexagonal phases on MBE-La2O3 templated-GaN(0001) when the film is thicker than 15 nm. The stabilization of a thin cubic La2O3 phase could be related to a difference in the surface energy and the ALD growth temperature.

Facile preparation and characterization of lanthanum oxide powders by the calcination of lanthanum carbonate hydrate in microwave field

Micron-sized lanthanum oxide powders are prepared by the calcination of lanthanum carbonate hydrate in microwave field. The decomposition process of lanthanum carbonate hydrate was analyzed by TG-DSC and indicates the reaction undergoes three stages, resulting in the generation of lanthanum oxide at 770 °C. For microwave assisted calcination, XRD patterns demonstrate that hexagonal La2O3 structure is initially formed after calcination at 650 °C for 2 h, and FT-IR analyses confirm the decomposition of precursor is complete after calcination at 750 °C for 2 h. SEM investigations reveal that 800 °C is the optimal calcination temperature to generate La2O3 powders with uniform morphologies. In comparison, conventionally calcination experiments are carried out in electrical furnace. Both XRD and FT-IR analyses are in consistence with TG-DSC, which indicate the temperature required for fully decomposition of lanthanum carbonate hydrate by conventional heating is higher than that of microwave heating. SEM images present irregular morphologies and wide particle size distribution of conventionally prepared samples. All the techniques are utilized to prove the feasibility of decomposing La2(CO3)3 to generate La2O3 in microwave field and highlight the advantages of microwave heating.

Ni/La2O3 Catalysts for Dry Reforming of Methane: Insights into the Factors Improving the Catalytic Performance

AbstractTo understand the structure‐reactivity relationship of Ni/La2O3, and eventually get more applicable catalysts for DRM, glycine nitrate combustion (GNC), precipitation (PP) and thermal decomposition (TD) methods have been used to prepare La2O3 supports. Although all the supports possess a hexagonal La2O3 phase, their bulk and surface properties are significantly changed. By using them as supports, the interactions between NiO/Ni and La2O3 are varied, thus achieving Ni/La2O3 catalysts with different activity, stability and anti‐coking ability, which follow the order of 5Ni/La2O3‐GNC>5Ni/La2O3‐PP>5Ni/La2O3‐TD. On La2O3 having a higher surface area, a catalyst with a higher active metallic Ni surface area can be achieved. Therefore, the interfaces between Ni and La2O2CO3 can be enlarged, which effectively facilitates the reaction between carbon deposits and the La2O2CO3 formed during the DRM, thus preventing the accumulation of both and keeping the catalyst surface clean, active and stable. In addition, the amount of surface alkaline and active oxygen sites of the reduced catalysts obey the order of 5Ni/La2O3‐GNC>5Ni/La2O3‐PP>5Ni/La2O3‐TD, which is well consistent with the reaction performance. Therefore, these two factors are also believed to be critical to decide the reaction performance. It is concluded that Ni/La2O3 catalysts with high activity, stability and potent anti‐coking ability for DRM can be achieved by preparing catalysts with high Ni dispersion.

Structural, photoluminescence and thermoluminescence study of novel Li+ co-activated lanthanum oxide activated with Dy3+ and Eu3+ obtained by microwave-assisted solution combustion synthesis

Stimulated luminescence of novel La2O3 nanophosphors doped with Dy3+ and Eu3+ and co-activated with Li+, prepared by microwave-assisted solution combustion synthesis, was investigated for the very first time. X-ray diffraction results indicated hexagonal La2O3 crystalline phase. Lanthanide and Li+ doping did not affect the La2O3 crystal structure. Scanning electron microscopy images showed nanoparticle morphologies such as plates, rods and irregular shapes. Photoluminescence spectra of La2O3:Dy3+, Li+ exhibited blue and green emission bands due to Dy3+ transitions. For La2O3:Eu3+, Li+, sharp emission lines, corresponding to the optical transitions of Eu3+ were observed. Thermoluminescence glow curve of La2O3:Dy3+, Li+ previously exposed to beta radiation exhibited a prominent glow peak located at ∼46 °C, possibly useful for after-glow or persistent luminescence applications, whereas La2O3:Eu3+, Li+ curve, displayed three intense peaks at ∼50, ∼110 and ∼150 °C. Thermoluminescent signal repeatability and decay curve asymptotic behaviour could place La2O3:Eu3+, Li+ as suitable for medium and high-dose radiation dosimetry applications.

Atomic layer deposition of lanthanum oxide with heteroleptic cyclopentadienyl-amidinate lanthanum precursor - Effect of the oxygen source on the film growth and properties

La2O3 thin films were deposited by atomic layer deposition from a liquid heteroleptic La precursor, La(iPrCp)2(iPr-amd), with either water, ozone, ethanol, or both water and ozone (separated by a purge) as the oxygen source. The effect of the oxygen source on the film growth rate and properties such as crystallinity and impurities was studied. Saturation of the growth rate was achieved at 225 °C with O3 as the oxygen source. With water, very long purge times were used due to the hygroscopicity of La2O3 but saturation of the growth rate was not achieved. Interestingly, when an O3 pulse was added after the water pulse with a purge in between, the growth rate decreased and the growth saturated at 200 °C. With ethanol lanthanum hydroxide was formed instead of La2O3 at 200–275 °C whereas hexagonal La2O3 films were obtained at 300 °C but the growth was not saturative. Using the separate pulses of water and ozone in the same deposition provided the best results from the four studied deposition processes. After annealing the films deposited with the La(iPrCp)2(iPrAMD)/H2O/O3 process showed pure hexagonal phase in all the films regardless of the deposition temperature, whereas mixtures of cubic and hexagonal La2O3 were seen with the other processes.

Optical properties of nanocrystalline La2O3 dielectric films deposited by radio frequency magnetron sputtering

La2O3 thin films were successfully synthesized by r. f. magnetron sputtering technique. The effect of power, deposition time and substrate temperature on the formation and optical properties of the films was investigated. X-ray diffraction (XRD) studies revealed the formation of hexagonal phased La2O3 thin films. The influence of sputtering parameters on chemical composition and surface species was studied by X-ray photoelectron spectroscopy (XPS). The optical properties were investigated in the wavelength range of 200–1100 nm. The samples were modelled as a three-phase optical model. Optical constants were calculated at 2 eV from classical dispersion model based on the single Lorentz for dielectric materials.