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AlN is regarded as a promising ceramic material for high performance structural and high temperature applications due to its superior properties such as high thermal conductivity, excellent stability and wear resistance. However, challenges remain in fabricating AlN ceramics with high strength and high thermal shock resistance. In this work, AlN/YAlO 3 composites with different YAlO 3 contents (3–10 wt%) were prepared by a simple pressureless sintering method, and the impact of YAlO 3 content on mechanical properties and thermal shock resistance of AlN/YAlO 3 composites was investigated. Results show that the grain growth of AlN is inhibited and the densification is improved with the addition of 3 wt% and 5 wt% YAlO 3. Hence, the flexural strength and fracture toughness of AlN/YAlO 3 composites are improved due to the grain refinement and compactness enhancement, and the highest value, 369 MPa and 3.84 MPa m1/2, are reached by the AlN-5 wt% YAlO 3 composite. Moreover, the thermal shock resistance was assessed through theoretical forecast and cyclic thermal shock tests over a temperature range between 1000 °C and 1600 °C. Comparing with pure AlN, the thermal stress damage resistance parameters (R IV ) of AlN/YAlO 3 composites were increased, while their residual strengths and retention ratios after 10–50 cycles of thermal shock tests maintained a higher level as well. Microstructure analysis revealed that the thermal shock resistance of AlN/YAlO 3 composites was evidently improved attributing to various strengthening mechanisms such as crack deflection, crack branching and microcrack toughening. [ABSTRACT FROM AUTHOR]

Y-Al-O oxides are characterized to be primary nanoprecipitates in oxide dispersion strengthened (ODS) Ni-based alloys for Very High Temperature Reactor (VHTR). We reported a first-principles study to assess the mechanical properties and helium behaviors in YAlO3(YAH) strengthened Ni-based ODS alloys from the nickel grain boundary and YAlO3 bulk to the Ni/ YAlO3 interface. The results suggest that YAH shows a elastic manner and well deformation compatibility with the matrix. The oxide strengthened system is expected to inhibit the formation of helium bubbles by capturing helium atoms dispersedly in YAlO3 bulk and Ni/ YAlO3 interface and thus hinder the He induced embrittlement.These findings provide basic understandings of the helium behaviors in a Al-cotnaining Ni-based ODS alloy.

Ceramic pigments based on chromium-doped yttrium aluminate (YAl 1-X Cr X O 3 ; x = 0.01; 0.03 and 0.05 mol%) were obtained by using chemical combustion method. Chemical processes with and without the use of mineralizers were employed. The modifications in the structure, morphology, optical and thermal properties caused by the inserted agents in the aluminate network were investigated by means of the following techniques: X-ray diffraction (XRD), Rietveld refinement, diffuse reflectance spectroscopy in the ultraviolet–visible region (UV–Vis), Fourier-transform infrared (FTIR) spectroscopy, field emission gun scanning electron microscopy (FEG-SEM), and CIELab colorimetric coordinates. The pigments were applied to ceramic pieces and the color stability was evaluated. XRD patterns results coupled with Rietveld refinement analyses showed a pronounced phase evolution for the samples containing mineralizers. This confirmed the effectiveness of these constituents for the formation of yttrium aluminate perovskite phase. The UV–Vis spectra showed greater reflectance in samples without mineralizers, while FTIR spectroscopy Analysis showed bands of vibration related to Al3+ coordinated octahedrally for both systems. Samples with the presence of mineralizer agents showed morphology similar to a cube with the presence of primary aggregated particles as revealed by FEG-SEM. The colorimetric pigments data showed values of the a* coordinate, which is related to red color components. This value was higher for the powder in the system with mineralizers as well as in the pigments that were employed on the ceramic pieces. [ABSTRACT FROM AUTHOR]

The paper presents and discusses the results of performed calculations for YAlO3 (111) surfaces using a hybrid B3LYP description of exchange and correlation. Calculation results for SrTiO3, BaTiO3 and BaZrO3 (111) as well as YAlO3, SrTiO3, BaTiO3 and BaZrO3 (001) surfaces are listed for comparison purposes in order to point out systematic trends common for these four ABO3 perovskite (001) and (111) surfaces. According to performed ab initio calculations, the displacement of (001) and (111) surface metal atoms of YAlO3, SrTiO3, BaTiO3 and BaZrO3 perovskite, upper three surface layers for both AO and BO2 (001) as well as AO3 and B (111) surface terminations, in most cases, are considerably larger than that of oxygen atoms. The YAlO3, SrTiO3, BaTiO3 and BaZrO3 (001) surface energies for both calculated terminations, in most cases, are almost equal. In contrast, the (111) surface energies for both AO3 and B-terminations are quite different. Calculated (111) surface energies always are much larger than the (001) surface energies. As follows from performed ab initio calculations for YAlO3, SrTiO3, BaTiO3 and BaZrO3 perovskites, the AO- and BO2-terminated (001) as well as AO3- and B-terminated (111) surface bandgaps are almost always reduced with respect to their bulk bandgap values. [ABSTRACT FROM AUTHOR]

With consideration about the different termination conditions of atomic layer, six kinds of YAlO 3 (001)/TiC(100) coherent interface models were selectively constructed based on the results of lattice mismatch calculation and surface convergence test. The work of adhesion and interfacial energy were calculated by first principles method, which is used to analyze their interface adhesive strength and stability to find out interface structures with excellent property. Charge density difference and electron localization functions were calculated to analyze interfacial atomic bonding characteristics. The YAlO 3 (001)/TiC(100) interfacial structure with the best grain boundary crack and displacement resistance were predicted by the adhesive sliding simulation and potential barrier calculation of preferable formed interfacial structures. The calculation results show that the lattice mismatch of YAlO 3 (001)/TiC(100) interfacial structures is very small, about 2.5%, which indicates they have the advantage of forming coherent interfaces. The work of adhesion of O1-Ti interface is the largest (W ad = 5.74 J/m2), which is followed by that of the O1-C interface (W ad = 5.73 J/m2). Their interface structures are similar and interfacial atomic bond type are both mixture of covalent bond (between O atom and C atom) and ionic bond (between O atom and Ti atom). However, the interfacial energy of O1-C is the smallest (γ = 2.16 J/m2), which reveals that the O1-C type YAlO 3 (001)/TiC(100) interface is the most stable. In addition, the sliding direction static friction force of O1-C model is 1.24 times larger than that of O1-Ti, and most of the O1-C interfacial barrier is larger than that of O1-Ti structure in a sliding period. Therefore, it can be predicted that a YAlO 3 (001)/TiC(100) interface with excellent combination property will be preferable formed in type of O1-C structure. The densification and mechanical property are expected to be greatly improved in TiC reinforced wear-resistance coating and other functional ceramics after adding YAlO 3 additive. Image 1 • The work of adhesion and interfacial energy were calculated. • Interfacial electronic structures between YAlO 3 and TiC were analyzed. • Interfacial bond characteristics were revealed by charge density difference and ELF. • The adhesive sliding between YAlO 3 and TiC was investigated. [ABSTRACT FROM AUTHOR]

Inorganic ultraviolet-electroluminescent (UV-EL) devices with a Gd3+-doped YAlO 3 thin film emitting layer were fabricated by radio frequency sputtering. Three kinds of perovskite-type oxide substrates, namely a SrTiO 3 single crystal (STO-SC), BaTiO 3 single crystal (BTO-SC), and BaTiO 3 polycrystalline disk (BTO-PC), were used for the devices. The influence of the substrates on the UV-EL properties of YAlO 3 :Gd3+ was investigated. It was found that EL threshold voltage, emitting locations, and EL intensity have changed depending on the substrates. The UV-EL attributed to the 6P J -8S 7/2 transitions in Gd3+ was observed in the BTO-PC substrate device with applied voltage of approximately over 200 V and in the STO-SC and BTO-SC substrate devices with that of approximately over 500 V. The STO-SC and BTO-SC devices showed EL only near the edges of a back electrode, whereas the BTO-PC device showed surface EL over the whole electrode. It was considered the local EL at the electrode edges in the SC substrate devices was caused by a concentrated electric field in the vicinity of the electrodes. The BTO-PC device showed not only the lowest EL threshold voltage but also the most intense EL in the three devices. Because the BTO-PC substrate has a high dielectric constant and appropriate surface roughness, which results in a high and uniform electric field over the back electrode, the YAlO 3 :Gd3+ emitting layer showed intense surface UV-EL with lower applied voltage. [ABSTRACT FROM AUTHOR]

Abstract The characteristics of YAlO 3 /NbC heterogeneous nucleation interface are strongly associated with the interfacial structure, electronic construction and properties. The lattice mismatch between low index crystal faces of YAlO 3 and NbC was calculated by using the Bramfitt two-dimensional lattice mismatch theory. The work of adhesion, interfacial energy and electronic structure of the YAlO 3 (001)/NbC(100) interface structures were calculated by the first principles method. The charge density difference, electron localization function and crystal orbits overlap population were adopted to analyze the charge transfer and bond characteristics. The microstructure of surfacing alloy was observed by transmission electron microscopy (TEM). The results show that, the two-dimensional lattice mismatch of YAlO 3 (001)-NbC(100) interface is 5.4%, which testifies that YAlO 3 can meet the lattice structure condition of being an effective heterogeneous nucleus of NbC. In all interface structures, the work of adhesion of C-O2 model is the largest (W ad = 6.558 J/m2) and the interfacial energy of C-Y model is the smallest (γ = 0.54 J/m2). It can be confirmed that the C-Y interface structure is the most stable one, whose interfacial energy is the smallest. The chemical bonds between interface atoms of all models are major covalent bonds and few metal bonds. The calculation results indicate that YAlO 3 (001) slab and NbC(100) slab can form a stable interface structure. The TEM results verify that the rare earth compound in NbC particle is YAlO 3. In addition, NbC growth encircling YAlO 3 and they are combined tightly. Therefore, YAlO 3 can act as the effective heterogeneous nucleus of NbC and refine it. Graphical abstract Image 1 Highlights • Work of adhesion and interfacial energy were calculated to analyze interfacial bonding strength and stability. • Interfacial electronic structures were analyzed by charge density difference. • Interfacial bond characteristics were revealed by ELF and COOP. • The heterogeneous nucleation interface of YAlO 3 and NbC was observed by TEM. [ABSTRACT FROM AUTHOR]

Abstract Recent works describing the existence of an intense-blue color within the YIn 1-x Mn x O 3 solid solution due to the presence of Mn3+ cations in trigonal-bipyramidal sites have led to the interest to prepare Al-analogues with the same 5-fold non-centrosymetric coordination. In this framework, YAlO 3 structure has been recently re-examined, concluding the aluminate is indeed an oxycarbonate with the Y 3 Al 3 O 8 CO 3 stoichiometry. In this work, we observed that pure yttrium aluminate is not only obtained for fast thermal treatments below 1000 °C but with higher Al:Y ratio than 1:1. YAl 1.15 (CO 3) y O 3+δ. The corresponding YAl 1.15-x Mn x (CO 3) y O 3+δ solid solutions were successfully prepared showing dull brown colors for the low Mn-content in comparison to Yin 1-x Mn x O 3 series, confirming that the TBP coordination is lost in the aluminate, partly due to the presence of carbonate groups in the structure. Graphical abstract Image 1 Highlights • Pure hexagonal YAlO 3 can be obtained with higher Al:Y ratio than 1:1. • The corresponding oxide contains carbonate species, evidenced by TGA and IRTF. • YAl 1.15-x Mn x (CO 3) y O 3+δ solid solutions exhibit dull brown colors. • The absence of bright color is due to the loss of the 5-fold coordination for Mn. [ABSTRACT FROM AUTHOR]

By means of the hybrid exchange-correlation functionals, we performed predictive ab initio calculations for industrially most important ABO3 perovskites, like, BaTiO3, SrTiO3, CaTiO3, SrZrO3 and PbZrO3 (001), (011) and (111) surfaces as well as bulk and (001) surface F-centers. From another side we performed comparative ab initio calculations for charged and polar YAlO3 (001) surfaces. For BaTiO3, CaTiO3, SrZrO3 and PbZrO3 perovskite neutral (001) surfaces, in most cases, all upper surface layer atoms relax inwards, whereas all second surface layer atoms relax upwards, and again, all third surface layer atoms relax inwards. The atom relaxation pattern for YAlO3 polar and charged (001) surfaces is completely different from the ABO3 perovskite neutral (001) surfaces. The ABO3 perovskite (001) surface energies are practically equal for both AO and BO2-terminations, and they are considerably smaller than (011) and especially (111) polar and charged surface energies. The atomic displacement magnitudes of nearest neighbor atoms around the (001) surface F-center in ABO3 perovskites are considerably larger than the related displacement magnitudes of nearest neighbor atoms around the bulk F-center. In the ABO3 perovskites the electron charge is considerably better localized inside the bulk F-center than in the (001) surface F-center, where the oxygen vacancy charge is more delocalized over the nearest neighbor atoms than in the bulk Fcenter case. The (001) surface F-center formation energy in the ABO3 perovskites is smaller than the bulk F-center formation energy, which triggers the F-center segregation from the ABO3 perovskite bulk towards its (001) surfaces. In most cases the (001) surface F-center induced defect level in the band gap of ABO3 perovskites is located closer to the (001) surface conduction band bottom than the bulk F-center induced defect level to the bulk conduction band bottom. [ABSTRACT FROM AUTHOR]

Abstract The results of ab initio calculations of polar YAlO 3 (0 0 1) surfaces by means of a hybrid B3LYP exchange-correlation functional as it is implemented in the CRYSTAL computer code are presented. Both polar YO and AlO 2 -terminations of the cubic YAlO 3 (0 0 1) surface were considered. We performed relaxation of atoms on the upper three layers of both YO and AlO 2 -terminated YAlO 3 (0 0 1) surfaces using in our calculations slabs containing 22 and 23 atoms as well as 9 layers, respectively. We predict a significant increase of the Al-O chemical bond covalency on the AlO 2 -terminated YAlO 3 (0 0 1) surface with respect to the YAlO 3 bulk. Our calculated YO and AlO 2 -terminated YAlO 3 polar (0 0 1) surface energies are considerably larger than the related structure ABO 3 perovskite neutral (0 0 1) surface energies, but comparable with ABO 3 perovskite polar (0 1 1) surface energies. Our calculated optical band gap near the YO-terminated YAlO 3 (0 0 1) surface is decreased, but near the AlO 2 -terminated (0 0 1) surface is increased with respect to the calculated YAlO 3 bulk optical band gap. [ABSTRACT FROM AUTHOR]

Abstract The atomic structure and electronic properties of Mn3+ and Mn2+ ions substituted for the host Al at YAlO 3 have been studied from the first principles. The 2 × 2 × 2 supercell adopted for the bulk crystal phase of P b n m symmetry allows us to simulate substitutional point defect with concentration of about 3%. To perform ab initio modeling of Mn-doped YAlO 3 we were using approach of hybrid exchange-correlation functional HSE within density functional theory. We predict a decrease of the Mn O bond covalency in the doped crystal with respect to the Al O bond of ideal orthorhombic YAlO 3. Relatively large displacement of Y and Al atoms nearest to the F 0 -center inserted to stabilize the Mn2+ ion of Mn:YAlO 3 (0.17 Å towards the defect) influences the YAlO 3 electronic structure. This leads to the presence of energy levels in the band gap of Mn-doped YAlO 3. The F -center attracts ∼ 0.54 e, while the rest electron density from the missing O2− is localized mostly on the closest Mn2+ dopant. Highlights • The atomic and electronic structures of Mn3+ and Mn2+ ion doped YAlO 3 have been studied in deep from the first principles. • Decrease of the Mn-O bond covalency in the doped crystal with respect to the Al-O bond of ideal YAlO 3 is predicted. • The nature of energy levels in the optical band gap of Mn-doped YAlO 3 is thoroughly described. [ABSTRACT FROM AUTHOR]

In this work, phosphor materials with the formula YAlO 3 were synthesized via sol-gel method by using the stoichiometric amounts of yttrium nitrate and aluminum nitrate as base materials. The obtained phosphors were doped/co-doped with Tb3+, Nd3+ rare earth ions and Mn2+ transition metal ion. For evaluating the influence of the dopants, the grain size and morphology of the samples by scanning electron microscopy (SEM) and the phase and crystallinity of the synthesized materials by X-ray diffraction (XRD) were investigated. Optical absorption spectra, photoluminescence (PL) and thermoluminescence (TL) were performed to determine a relationship the changing dopant on luminescence properties of YAlO 3. Moreover, the kinetic parameters namely activation energy (E), order of kinetics (b) and frequency factor (s) of the synthesized pure and doped materials were calculated using Computerized Glow Curve Deconvolution (CGCD) and Peak Shape Method for a better understanding of the optical properties that change with the doping process. Strong green emission was detected in the sample doped with Mn2+ correspond to 4T 1 (G)→6A 1 (S) transition. As for YAlO 3 : Nd3+, characteristic emissions originated from 4G 11/2 → 4I 9/2 (∼423 nm), 4G 9/2 → 4I 9/2 (∼460 nm) and 4G 7/2 → 4I 9/2 (∼540 nm) transitions were seen. The optical band gap of undoped sample was calculated as 2.79 eV and depending on the presence of Nd3+ and Tb3+ dopant ions this value was decreased to the range 2.46–2.56 eV. • Strong green emission was detected correspond to 4T1(G)→6A1(S) transition of Mn2+. • Nd3+ and Tb3+ dopant ions caused to decreasing to the optical band gap. • Tb3+ ion was improved the TL glow curve intensity. [ABSTRACT FROM AUTHOR]

YAlO 3 crystals doped with different concentrations (0.05, 0.1, 1.0 at.%) of Pr3+ ions were studied in this work. The crystals were grown from the melt by a micro-pulling-down (MPD) method. Luminescence and energy-storage properties of YAlO 3 :Pr crystals were studied using cathodoluminescence (CL), as well as thermoluminescence (TL) and optically stimulated luminescence (OSL). Instead of a conventional optical illumination with blue LEDs, infrared light was used for optical stimulation (IRSL). For the YAlO 3 :Pr crystals both TL glow-curves and IRSL decay curves were extensively analyzed. Both d-f transitions in UV range and f-f transitions in the visible range of Pr3+ ions were observed including radiative transitions from 3P j (j = 0,1,2) to 3F 2,3,4 and 3H 4,5,6 levels. The highest CL signal was measured for the lowest Pr3+ concentration of 0.05 mol% and a strong luminescence quenching was observed for the increase in the Pr3+ content. For the increasing dose of radiation, the intensity of the main TSL glow-peak at around 170–200 °C shows a linear behavior, regardless of the applied dopant concentration. Due to the highest TL and IRSL radio-sensitivity and stability in time after the irradiation, the YAlO 3 :Pr (0.05 mol%) perovskite seems most promising material for radiation measurement applications. • YALO 3 crystals made by micro-pulling-down technique have been investigated. • The crystals were doped with Pr3+ Rare-Earths ions. • Luminescence of Pr3+dopants was clearly observed. • Good embedded of Pr3+ions in YALO 3 matrix was confirmed. • YALO 3 with Pr3+ (0.05 mol%) was found to present the best dosimetric properties. [ABSTRACT FROM AUTHOR]

Thin films of YAlO3:Gd3+ and YAlO3:Gd3+Pr3+ were prepared on LaAlO3 (001) single crystal substrates by pulsed laser deposition (PLD). Both films were grown epitaxially and their surfaces were uniformly smooth. Under UV excitation at 216 nm, YAlO3:Gd3+ film did not show any intense photoluminescence (PL); on the other hand, YAlO3:Gd3+Pr3+ film showed intense Gd3+ PL at 314 nm through Pr3+ 4f-5d absorption. Under electron irradiation with acceleration of 2.00 kV, both films showed UV cathodoluminescence (CL) from Gd3+ ions. In contrast to PL, the CL intensity of the YAlO3:Gd3+ film was four times greater than that of the YAlO3:Gd3+Pr3+ film. The PL excitation spectrum of YAlO3:Gd3+ in vacuum UV region revealed the presence of an intense excitation band at 155 nm assignable to YAlO3 host absorption. This observation implied that the energy of accelerated electrons was absorbed by the host and then transferred to Gd3+. Pr3+ co-doping was found to weaken the Gd3+ emission in CL because the excitation energy absorbed by the host was transferred to not only Gd3+ but also Pr3+ accompanying visible emission and nonradiative transition in Pr3+. [ABSTRACT FROM AUTHOR]

Highlights: [•] Tb and Eu doped cubic garnet YAlO3 phosphors were prepared by sol–gel method. [•] The optical and structural properties of both phosphors were investigated. [•] Photoluminescence decay is double-exponential with short and long lifetimes. [•] The lifetimes are ascribed to the ions on the surface and in the bulk of the powder. [ABSTRACT FROM AUTHOR]

Abstract: Gd3+–Pr3+ codoped YAlO3 perovskite was found to show an intense ultraviolet emission from Gd3+ ions under photo-excitation at 215nm. The emission peak was observed at 314nm with narrow peak width and assigned to the 4f–4f transition of 6P7/2–8S7/2 in Gd3+ ions. Three peaks at 245, 255nm and 277nm were observed in the excitation spectra of Gd3+ doped YAlO3 and they were attributed to the f–f transition of 8S7/2–6DJ or 8S7/2–6IJ in Gd3+ ions. In addition to the three peaks, an intense broad excitation band was newly observed at around 215nm in the excitation spectra of Gd3+–Pr3+ codoped YAlO3. Taking account of the absorption spectra of Gd3+ doped and Gd3+–Pr3+ codoped YAlO3, the broad excitation band was ascribed to the 4f–5d transition in Pr3+ ions. The intensity of the UV emission from Gd3+–Pr3+ codoped YAlO3 was approximately 8 times larger than that from Gd3+ doped YAlO3 at optimal dopant concentration and excitation wavelength. It was considered that the intense emission in Gd3+–Pr3+ codoped YAlO3 was derived from the large absorption of excitation energy by Pr3+ ions and the energy transfer from Pr3+ to Gd3+ ions. [Copyright &y& Elsevier]

Abstract: The thermal shifts of R-line for isoelectronic 3d3 ions Cr3+ and Mn4+ in YAlO3 crystal are studied by using a new theoretical expression including both the static contribution due to lattice thermal expansion and the vibrational contribution due to electron–phonon interaction. The new expression in form is almost the same as that containing only the vibrational contribution (which is widely-used in the previous papers) except the change of coefficient from α to α′+A (where α, obtained from the old expression, and α′, obtained from the new expression, are the apparent and true electron–phonon coupling parameters, respectively. A is a parameter concerning the static contribution). By using the new expression and the analysis of pressure- and temperature-dependences of R-line, it is found that the static contribution to the thermal shift of R-line in sign is contrary to and in magnitude is about 36% of the vibrational one. Thus, the electron–phonon coupling parameters α′ increase about 36% compared with the corresponding parameters α for both Cr3+ and Mn4+ in YAlO3 crystal. So, for the reasonable explanation of thermal shifts of spectral lines and the determination of the true electron–phonon coupling parameter, both the static and vibrational contributions to thermal shift should be taken into account. The reason that the electron–phonon coupling parameter |α′| of Mn4+ is larger than that of Cr3+ in YAlO3 crystal is discussed. [Copyright &y& Elsevier]

Abstract: YAlO3:Ni2+ (0.1mol%) doped nanophosphor was synthesised by a low temperature solution combustion method. Powder X-ray diffraction (PXRD) confirms the orthorhombic phase of yttrium aluminate (YAlO3) along with traces of Y3Al5O12. Scanning Electron microscopy (SEM) shows that the powder particles appears to be spherical in shape with large agglomeration. The average crystallite sizes appeared to be in the range 45–90nm and the same was confirmed by transmission electron microscopy (TEM) and Williamson–Hall (W–H) plots. Electron Paramagnetic Resonance (EPR) and photoluminescence (PL) studies reveal that Ni2+ ions are in octahedral coordination. Thermoluminescence (TL) glow curve consists of two peaks with the main peak at ∼224°C and a shouldered peak at 285°C was recorded in the range 0.2–15kGy γ-irradiated samples. The TL intensity was found to be increasing linearly for 224°C and 285°C peaks up to 1kGy and thereafter it shows sub-linear (up to 8kGy) and saturation behavior. The trap parameters namely activation energy (E), order of kinetics (b), frequency factor (s) at different γ-doses were determined using Chens glow peak shape and Luschiks methods then the results are discussed in detail. Simple glow peak structure, the 224°C peak in YAlO3:Ni2+ nanophosphor can be used in personal dosimetry. [Copyright &y& Elsevier]

Abstract: The YAP:Mn single crystalline films (SCF) have been crystallized by liquid phase epitaxy (LPE) method onto YAP substrates. The cathode- (CL) and photo-luminescence (PL) spectra of the YAP:Mn SCF were analyzed for determination of the preferable valence states of manganese ions which are realized in these SCF depending on Mn content in the 0.01–0.81at.% range. The thermoluminescence (TL) properties of YAP:Mn SCF with the different Mn content above the RT range were also examined in comparison with the properties of YAP:Mn single crystal counterpart. We show that YAP:Mn (0.01at.%) SCF possesses effective TL properties both under α-particle and γ-quanta excitation with main TSL peaks at 130 and 195°C. We assume that the different valence states of Mn ions are responsible for their TL properties, e.g. both emission and trapping centers in YAP:Mn are formed mainly by the different valence states of Mn ions. [Copyright &y& Elsevier]

Abstract: Ionoluminescence (IL) and photoluminescence (PL) spectra for different rare earth ions (Sm3+ and Dy3+) activated YAlO3 single crystals have been induced with 100MeV Si7+ ions with fluence of 7.81×1012 ionscm−2. Prominent IL and PL emission peaks in the range 550–725nm in Sm3+ and 482–574nm in Dy3+ were recorded. Variation of IL intensity in Dy3+ doped YAlO3 single crystals was studied in the fluence range 7.81×1012–11.71×1012 ionscm−2. IL intensity is found to be high in lower ion fluences and it decreases with increase in ion fluence due to thermal quenching as a result of an increase in the sample temperature caused by ion beam irradiation. Thermoluminescence (TL) spectra were recorded for fluence of 5.2×1012 ionscm−2 on pure and doped crystals at a warming rate of 5°Cs−1 at room temperature. Pure crystals show two glow peaks at 232 (Tg1) and 328°C (Tg2). However, in Sm3+ doped crystals three glow peaks at 278 (Tg1), 332 (Tg2) and 384°C (Tg3) and two glow peaks at 278 (Tg1) and 331°C (Tg2) in Dy3+ was recorded. The kinetic parameters (E, b s) were estimated using glow peak shape method. The decay of IL intensity was explained by excitation spike model. [Copyright &y& Elsevier]

Abstract: Crystal field (CF) analysis of energy levels for Nd3+ and Er3+ ions in LaAlO3, YAlO3, and LaGaO3 single crystals is presented. It is shown that a combined approach comprising the ascent/descent in symmetry (ADS) method combined with superposition model (SPM) analysis can be successfully used for analysis of low-symmetry systems. The present ADS/SPM approach is less labor and time consuming as compared, e.g., with Monte-Carlo method and it also allows maintaining the relationship between the crystallographic axis system and the nominal axis systems of fitted CFP sets. For orthogallates and orthoaluminates the actual Cs symmetry, resulting from distortion of perovskite structure, may be successfully approximated for both systems by the ADS chain C4v ↔C3 (D3)↔Cs or C3 (D3)↔Cs symmetry. The possibility of using of approximated symmetries for orthogallates or orthoaluminates can be useful for interpretation of energy levels for this family of compounds of technological importance, particularly in the case when the number of available experimental energy levels is insufficient for full Cs parameterization. The novel aspect of the combined ADS/SPM approach is that possible higher symmetry approximations employing also the axis systems oriented differently than for the actual symmetry are searched for, taking advantages of the transformation properties of CF parameters sets. [Copyright &y& Elsevier]

Room-temperature-polarized single-crystal Raman spectra have been measured for both GdAlO and YAlO. Both aluminates crystallize in the orthorhombic (Pbnm) perovskite structure. Of the 24 possible Raman modes in 4 symmetries, 20 and 17 modes were observed for gadolinium and yttrium aluminates, respectively. Comparisons of the Raman spectra of these two aluminates to those of 28 other orthorhombic ABO perovskites revealed remarkably similar spectral patterns, regardless of chemistry or valency of the cations. Closer examination of the effect of mass, valencies, and size of the cations on the Raman spectra versus composition revealed that for the observed modes, the A cation plays the dominant role in determining the Raman shift. In particular, the one to two lowest energy modes in each symmetry are determined by cation mass and valency no matter what the chemistry. For some perovskites with common A cations, higher energy modes were also strikingly similar. In particular, the calcium perovskites had almost all A modes at the same energies despite the greatly varying B cations. The second to the lowest mode in A and B depended only on A cation mass for all perovskites. The volume plays a minor role throughout but is hard to separate from mass effects because the most massive cations are also the largest. However, if the B-cation is common, for example, aluminates or ferrites, the volume has a minor effect on the higher energy modes. These trends were not observed for all perovskites. Notable exceptions were found if a perovskite is near a phase transition or metastable, as found for three manganites. The effect of increased valency of the A cation from 2-4 to 3-3 perovskites expresses itself as relatively larger Raman shifts for the lowest energy modes. Analog studies of MgSiO perovskites should be undertaken with only 2-4 perovskites. The increased understanding for the mode distributions of perovskites allows for better estimates of their thermodynamic properties through vibrational modeling. [ABSTRACT FROM AUTHOR]

Abstract: First-principles calculations are performed to investigate the crystal structure, electronic properties, the elastic properties, hardness and thermodynamic properties of YAlO3. The calculated ground-state quantities such as lattice parameter, bulk modulus and its pressure derivative, the band structure and densities of states were in favorable agreement with previous works and the existing experimental data. The elastic constants Cij , the aggregate elastic moduli (B, G, E), the Poisson’s ratio, and the elastic anisotropy have been investigated. YAlO3 exhibits a slight elastic anisotropy according to the universal elastic anisotropy index AU =0.24. The estimated hardness for YAlO3 is consistent with the experimental value, and Al–O bond in AlO6 octahedra plays an important role in the high hardness. The Y–O bonds in YO12 polyhedra exhibit different characteristic. Using the quasi-harmonic Debye model considering the phonon effects, the temperature and pressure dependencies of bulk modulus, heat capacity and thermal expansion coefficient are investigated systematically in the ranges of 0–20GPa and 0–1300K. [Copyright &y& Elsevier]

Abstract: YAlO3 (YAP) powders were successfully synthesized by a unique molten salt method, where YAP precursor was prepared by an electrochemical method at room temperature, followed by calcining it at a temperature of not exceeding 400°C for 8h using LiNO3 as the molten salt medium. XRD analysis and TEM observation show that well-crystallized YAP powders can be obtained at 400°C for a holding time of 8h with 1:16 ratio of YAP precursor to LiNO3 by weight. Greatly reduced temperature of forming YAP should be attributed to the incorporation of LiNO3 salt in preparing process. [Copyright &y& Elsevier]

The phase formation kinetics of YAP (YAlO3) synthesized through the polymeric precursor method was investigated by thermal analysis, X-ray diffraction and FT-IR spectroscopy. We demonstrated that the YAP synthesis is highly dependent on the heat and mass transport during all stages of the synthesis route. In the first stages, during the preparation of amorphous precursor, “hot spots” need to be suppressed to avoid the occurrence of chemical inhomogeneities. Very high heating rates combined with small amorphous particles are advantageous in the last stage during the formation of crystalline phase. We were able to synthesize nanosized particles of YAP single phase at temperatures around 1100 °C for future preparation of phosphors or ceramics for optics. [ABSTRACT FROM AUTHOR]

The electron paramagnetic resonance g factors and the local structure for Ni3+ in LaAl0.9Ni0.1O3 (LAN), La0.75Y0.25Al0.99Ni0.01O3 (LYAN) and YAl0.9Ni0.1O3 (YAN) are theoretically studied from the perturbation formulas of the g factors for a 3d7 ion of low spin (S = 1/2) in tetragonally elongated octahedra. In these formulas, the contributions to the g factors from the tetragonal distortion, characterized by the tetragonal field parameters Ds and Dt are taken into account. According to the calculations, the ligand octahedra around Ni3+ are suggested to suffer 2% relative elongation along the [001] (or C4) axis due to the Jahn-Teller effect. [ABSTRACT FROM AUTHOR]

Abstract: Vibrational and dielectric properties of YAlO3 are investigated within the framework of density functional perturbation theory. The calculated zone center phonon frequencies and dielectric constants are in good agreement with available experimental data. Based on the theoretical values of the dielectric constants and the highest longitudinal IR phonon energy and using the phenomenological model of Lempicki and Wojtowicz, we investigate the scintillation properties of the YAlO3. [Copyright &y& Elsevier]

We report on upconversion (UC) luminescence in YAlO3 codoped with 0.3% Cr3+ and 6% Yb3+. At 10 K excitation around 10,400 cm−1 leads to red Cr3+ pair luminescence at 14,000 cm−1. The UC excitation spectrum of the red Cr3+ luminescence is very similar to the squared Yb3+ absorption spectrum. This demonstrates that two Yb3+ 2F7/2→2F5/2 excitations are involved in the UC process. From transient measurements, the UC mechanism is found to be dominated by an energy transfer step: Two excited Yb3+ ions simultaneously transfer their excitation energy to a nearby Cr3+ pair. [Copyright &y& Elsevier]

Green (5S2→5I8) upconverted emission in Ho3+-doped YAlO3 under infrared pump (in the spectral range between 730 and 950 nm) is reported. Polarized absorption, emission spectra, and excited state absorption (ESA) spectra were recorded together. Lifetime and power dependency measurements were performed. Possible schemes of upconversion mechanism and their numerical simulation based on a rate equation model are presented. [Copyright &y& Elsevier]

Several scintillation detectors containing LSO, YAP, and BGO crystals coupled to 5 mm in diameter beveled-edge large area avalanche photodiodes (LAAPD) were studied. These configurations were chosen to address requirements of high-resolution positron emission tomography (PET). The number of electron-hole pairs, the energy resolution for 511 keV γ-rays, detection efficiency, and timing properties were measured in various configurations to establish best operating conditions for these detectors. The obtained results point towards a possibility of replacing photomultiplier tubes (PMT) in PET with LAAPDs, leading potentially to more compact, reliable, and accurate systems [ABSTRACT FROM PUBLISHER]

In this paper, the density functional theory accompanied with linear combination of atomic orbitals (LCAO) method is applied to study the atomic and electronic structure of the Ti3+ and Ti2+ ions substituted for the host Al atom in orthorhombic Pbnm bulk YAlO3 crystals. The disordered crystalline structure of YAlO3 was modelled in a large supercell containing 160 atoms, allowing simulation of a substitutional dopant with a concentration of about 3%. In the case of the Ti2+-doped YAlO3, compensated F-center (oxygen vacancy with two trapped electrons) is inserted close to the Ti to make the unit cell neutral. Changes of the interatomic distances and angles between the chemical bonds in the defect-containing lattices were analyzed and quantified. The positions of various defect levels in the host band gap were determined. [ABSTRACT FROM AUTHOR]

Abstract: The local compressibilities of Cr3+ and Mn4+ octahedral clusters in YAlO3 crystal are investigated by means of the pressure-induced -line shifts. The results suggest that the local compressibility changes from cluster to cluster and both compressibilities of 3d3 impurity clusters are smaller than that of the corresponding Al3+ octahedral cluster in the host YAlO3 crystal. The causes of above results are discussed. [Copyright &y& Elsevier]

Abstract: The results of measurements of spectral dependence of diffraction efficiency of light-induced holographic gratings in YAlO3:Mn(0.5%) crystal are reported. The experimental data are interpreted as an effect of interaction of both refractive index changes and light-induced absorption associated with optical transition within photo-induced Mn5+ ions and intrinsic defect centers. Nature of the intrinsic traps involved in the process is discussed. [Copyright &y& Elsevier]

In this paper, we analysis the thermal shifts of six luminescence peaks (R 1 → Y 2,3,5 , R 1 → Z 3 , R 2 → Y 1 , R 2 → Z 3) in Nd3+-doped YAlO 3 crystal with a full expression including both the static effect (characterized by the static parameter A) from lattice thermal expansion and the dynamic effect (characterized by the electron-phonon coupling parameter α′) originating from the electron-phonon interaction. The static effect is evaluated from the pressure shift of the spectral peak. The two thermal shift parameters A and α′ for these peaks are attained by means of an approximate treatment on the full expression. The results indicate that differing from the previous opinion, even in the 'hard' crystal YAlO 3 :Nd3+, the static effects to thermal shifts of most peaks are important and cannot be ignored. The estimated thermal shift parameters A and α′ for the spectral peaks of YAlO 3 :Nd3+ in order of magnitude are the same as those of various 4fn ions in crystals found previously and can be seen as reasonable. The cause of negative static parameters A (which were not reported previously) for some peaks is discussed. [ABSTRACT FROM AUTHOR]

Ceramic matrix composites (CMCs) are promising materials for high-temperature applications. Environmental barrier coatings (EBCs) are needed to protect the components against water vapor attack. A new potential EBC material, YAlO3, was studied in this paper. Different plasma-spraying techniques were used for the production of coatings on an alumina-based CMC, such as atmospheric plasma spraying (APS) and very low pressure plasma spraying (VLPPS). No bond coats or surface treatments were applied. The performance was tested by pull–adhesion tests, burner rig tests, and calcium-magnesium-aluminum-silicate (CMAS) corrosion tests. The samples were subsequently analyzed by means of X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Special attention was paid to the interaction at the interface between coating and substrate. The results show that fully crystalline and good adherent YAlO3 coatings can be produced without further substrate preparation such as surface pretreatment or bond coat application. The formation of a thin reaction layer between coating and substrate seems to promote adhesion. [ABSTRACT FROM AUTHOR]