Search query: (AlxCr1 − x)2O3

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abstract: Detailed structural and optical properties of a (AlxCr1 x)2O3 (0 x 1) synthesized by the solid state reaction method have been investigated. Single phase a (AlxCr1 x)2O3 with space group R 3 c is obtained for the full composition range of 0 x 1. Variations in the lattice parameters a and c have been determined. Lattice parameter c follows Vegard's law, while the lattice parameter a shows a clear deviation with a bowing parameter of 0.035 A. This behavior of the lattice parameters of a (AlxCr1 x)2O3 with x is explained in detail by studying the local structure. Extended x ray absorption fine structure spectroscopy shows a reduction in the values of Cr O bond lengths with composition x. Optical absorption measurements of a (Al1 xCrx)2O3 for 0 x 1 show a large bandgap tunability of 1.9 eV (from 3.4 eV to 5.3 eV) The photoemission spectroscopy data and the analysis of partial density of states obtained from first principles electronic structure calculations suggest that the valence band maxima is mainly composed of Cr 3d levels, which hybridize with the O 2p levels. Increased contribution of O 2p partial density of states is observed with Al substitution, which is expected to enhance p type carrier conduction in the a (AlxCr1 x)2O3 system as compared to the parent a Cr2O3 system. Thus, the large bandgap, its tunability in the UV region, and the predicted enhancement of p type conductivity in the a (AlxCr1 x)2O3 system make it a potential candidate for application in UV based photo detectors and transparent electronics.
author_names: Ravindra Jangir

Velaga Srihari

Ashok Bhakar

C Kamal

Pankaj R Sagdeo

Dharmendra Kumar

Shilpa Tripathi

S N Jha

Tapas Ganguli
title: Structural and optical properties of transparent, tunable bandgap semiconductor: a (AlxCr1 x)2O3
year: 2020

abstract: Density Functional Theory applying the generalised gradient approximation is used to study the phase stability of (AlxCr1 x)2O3 solid solutions in the context of physical vapour deposition (PVD) Our results show that the energy of formation for the hexagonal a phase is lower than for the metastable cubic g and B1 like phases independent of the Al content x. Even though this suggests higher stability of the a phase, its synthesis by physical vapour deposition is difficult for temperatures below 800 degC. Aluminium oxide and Al rich oxides typically exhibit a multi phased, cubic dominated structure. Using a model system of (Al0.69Cr0.31)2O3 which experimentally yields larger fractions of the desired hexagonal a phase, we show that point defects strongly influence the energetic relationships. Since defects and in particular point defects, are unavoidably present in PVD coatings, they are important factors and can strongly influence the stability regions. We explicitly show that defects with low formation ener.
author_names: Christian Martin Koller

Nikola Koutna

Jurgen Ramm

Szilard Kolozsvari

Jorg Paulitsch

David Holec

Paul H Mayrhofer
title: First principles studies on the impact of point defects on the phase stability of (AlxCr1 x)2O3 solid solutions
year: 2016

abstract: We report on structural and optical properties for ternary a (AlxCr1 x)2O3 (0 x 1) solid solutions synthesized by using solid sate reaction method. Single R 3c phase was obtained for the Aluminum composition of 0 x 1. Due to difference in the ionic radia of Al3+ and Cr3+ in plane lattice parameter showed deviation from the vegard's law. Optical absorption spectra for the solid solutions showed a blue shift of 0.5 eV in the optical gap. It has also been observed that Cr 3d level shifted towards the O 2p level in the valance band which indicates the enhancement of hybridization in the d and p levels, which is related to the delocalization of hole states, responsible for p type conduction in wide band gap semiconductors. The results suggests that ternary a (AlxCr1 x)2O3 (0 x 1) can be useful in the field of UV transparent electronics and UV photodetectors.We report on structural and optical properties for ternary a (AlxCr1 x)2O3 (0 x 1) solid solutions synthesized by using solid sate reaction method. Single R 3c phase was obtained for the Aluminum composition of 0 x 1. Due to difference in the ionic radia of Al3+ and Cr3+ in plane lattice parameter showed deviation from the vegard's law. Optical absorption spectra for the solid solutions showed a blue shift of 0.5 eV in the optical gap. It has also been observed that Cr 3d level shifted towards the O 2p level in the valance band which indicates the enhancement of hybridization in the d and p levels, which is related to the delocalization of hole states, responsible for p type conduction in wide band gap semiconductors. The results suggests that ternary a (AlxCr1 x)2O3 (0 x 1) can be useful in the field of UV transparent electronics and UV photodetectors.
author_names: Ravindra Jangir

Dharmendra Kumar

Velaga Srihari

Tapas Ganguli
title: Study on structural and optical properties of a (AlxCr1 x)2O3 (0 x 1) solid solutions
year: 2018

abstract: Abstract The (AlxCr1 x)2O3/Co granular systems were synthesised by a convenient sol gel method combined with autocombustion. Well crystallised samples are obtained after being annealed at 1073 K for 1 h and all of them possess a porous structure. Exchange bias effect of all the samples is investigated at different temperatures. Exchange bias field and coercivity are affected noticeably by Al concentration and temperature. The different magnetic behaviour of the samples can be well explained in terms of the domain state model. Temperature dependence of magnetisation for sample x 0 is investigated and a large irreversibility is observed in the whole temperature range.
author_names: S H Yang

Shu Jiang Liu

Y W Jiang

Sen Yang
title: Synthesis and exchange bias effect of (AlxCr1 x)2O3/Co granular systems
year: 2012

abstract: Abstract (AlxCr1 x)2O3 coatings were synthesised by cathodic arc evaporation applying DC and pulsed substrate bias voltages to study the impact of different bias duty cycle settings on structure and morphology as well as mechanical and tribological properties. X ray diffraction revealed a corundum type (AlxCr1 x)2O3 phase structure for Al contents x 0.5 and the formation of an additional face centred cubic (Al Cr O) phase for x 0.5 for the pulsed bias situation, independently of the chosen duty cycle. In general, changes of the duty cycle in the manner of decreasing the electron current time duration along with an extension of the ion bombardment during growth lead to a reduction of the coatings' domain size, the formation of compressive residual stress as well as increasing coating hardness and Young's modulus. An amorphous like coating microstructure accompanied with diminished mechanical properties was observed when a DC substrate bias voltage was applied. The investigations illustrate the potential of tuning the properties of arc evaporated oxide coatings by adjusting the energetic particle bombardment during growth.
author_names: Markus Pohler

Robert Franz

Jurgen Ramm

Peter Polcik

Christian Mitterer
title: Influence of pulsed bias duty cycle variations on structural and mechanical properties of arc evaporated (Al,Cr)2O3 coatings
year: 2015

abstract: Single layer and dual layer (AlxCr1 x)2O3 coatings were synthesised by cathodic arc evaporation with different Al contents to study their growth characteristics. It was demonstrated that variations in the Al content, the energy of incident particles and the coating thickness control the crystallinity and the coating texture. Analysis by X ray diffraction revealed a distinct (110) out of plane orientation after transition from a fine grained nucleation zone to a columnar growth mode. Furthermore, the impact of (AlxCr1 x)2O3 seed layers with x 0.25 and 0.5 on the growth of (AlxCr1 x)2O3 top layers with x 0.7 and 0.85 was evaluated in detail. According to X ray diffraction and transmission electron microscopy, the development of the corundum type crystal structure of the top layer was promoted by local epitaxy if the low Al containing seed layer exhibited a pronounced columnar structure. In this way, crystalline corundum type coatings with an Al content up to x 0.85 were obtained.
author_names: Markus Pohler

Robert Franz

Jurgen Ramm

Peter Polcik

Christian Mitterer
title: Seed layer stimulated growth of crystalline high Al containing (Al,Cr)2O3 coatings deposited by cathodic arc evaporation
year: 2014

abstract: Abstract Fe Al Cr alloys have excellent oxidation resistance at high temperature. Many studies have been carried out on their oxidation resistance mechanism, mainly on the role of Al, but there is a lack of understanding of the role of Cr. According to existing research results, the structure of the metal/oxide interface of Fe Al Cr alloys has been investigated by the density functional theory. Due to the third component, which is chromium, Al2O3 films can be rapidly formed on the surface of Fe Al Cr alloys. Based on the density functional theory, an Fe(110)/Al2O3(0001) interface model was established. The Cr atoms in the alloy diffused at the Fe(110)/Al2O3(0001) interface and replaced the Al atoms in high temperature enviorment, resulting in the formation of a multilayer oxide (AlxCr1 x)2O3. In this paper, X ray diffraction (XRD) Field emission scanning electron microscopy (FESEM) Energy dispersive spectroscopy (EDS) and other experimental methods were employed to validate the multilayer oxide structure model. By calculating the interfacial bonding energy, it was concluded that the presence of Cr in Fe/Al2O3 increases the interfacial bonding energy, but with the diffusion of Cr from the alloy matrix to the oxides, the bonding energy gradually decreases.
author_names: Jintao Wang

Shouping Liu

Xue Bai

Xiaohu Zhou

Xiao Han
title: Oxidation behavior of Fe Al Cr alloy at high temperature: Experiment and a first principle study
year: 2020

abstract: Abstract The Al rich Al Cr O films were directly deposited on Si(100) substrate by reactive radio frequency magnetron sputtering (RFMS) using Al Cr alloy targets. The elemental composition and phase structure of the films deposited from alloy targets with different Cr content at low substrate temperature were analyzed by electron probe microanalysis (EPMA) grazing incident X ray diffraction (GIXRD) and transmission electron microscopy (TEM) The results show that the single corundum structured (Al0.7Cr0.3)2O3 solid solution films could be successfully synthesized by sputtering the Al70Cr30 target at low substrate temperature of 550 The phase structures of the films deposited from Al80Cr20 target exhibit a mixture of Al rich a (AlxCr1 x)2O3, Cr rich a (AlxCr1 x)2O3, g Al2O3 and amorphous phases when the substrate temperature was lower than 550 The formation of g phase could be suppressed at 600 while few amorphous alumina still remains in the film. In order to deposit single phase corundum type Al rich (AlxCr1 x)2O3 solid solution films at low temperature, the sufficient Cr content in the films is required.
author_names: Y -T Cheng

Dongling Jiao

Z W Liu
title: The influence of Cr content on the phase structure of the Al rich Al Cr O films deposited by magnetron sputtering at low temperature
venue: Ceramics International
year: 2019

abstract: Abstract Various (AlxCr1 x)(O1 yNy) oxynitrides with different nitrogen non metal fractions y and two different multilayers thereof were developed by varying the synthetic air flow (without any other gas addition) during arc evaporation of powder metallurgically prepared Al0.70Cr0.30 cathodes. The (AlxCr1 x)(O1 yNy) oxynitride coatings crystallize with a single phase face centred cubic (fcc) (Al,Cr)N based structure for y 0.8, and with a phase composition of fcc (Al,Cr)2O3 like and corundum type a (Al,Cr)2O3 based structures for y The hardness of our as deposited (AlxCr1 x)(O1 yNy) oxynitrides, decreases from ~33 to 15 GPa with decreasing y from 0.8 to 0, while both multilayers demonstrate hardnesses of ~26 GPa. The onset temperature Tonset for thermally induced dissociation of Cr N bonds of our oxynitrides, to finally form Cr under N2 release, significantly increases from ~1000 to 1300 degC with decreasing N content y from 0.8 to 0.15. The multilayer with a smooth layer transition shows no mass loss up to the maximum temperature of 1500 degC, whereas that with a steep layer transition shows a mass loss due to N2 release with Tonset ~1250 degC. Dynamic oxidation treatments of our coatings in synthetic air up to 1500 degC indicate increased structural stability with decreasing nitrogen content y. Based on our results we can conclude, that by varying the synthetic air flow during arc evaporation of Al Cr cathodes (here, Al0.70Cr0.30) (AlxCr1 x)(O1 yNy) oxynitrides with y 0.8 can be prepared, having excellent mechanical properties and thermal stabilities.
author_names: R Raab

Christian Martin Koller

Helmut Riedl

Szilard Kolozsvari

Jurgen Ramm

Paul H Mayrhofer
title: The influence of synthetic air flow on the properties of arc evaporated Al Cr O N coatings
venue: Thin Solid Films
year: 2019

abstract: Abstract The thermal stability of cathodic arc evaporated Al0.70Cr0.30 based AlxCr1 xN/(AlxCr1 x)2O3 multilayer coatings and their monolithic constituents was investigated by combining differential scanning calorimetry and thermal gravimetric analysis with X ray diffraction and transmission electron microscopy investigations. The formation of volatile Cr oxides within the monolithic (Al,Cr)2O3 coating is suggested by a depletion of Cr during annealing treatments beginning with ~1050 degC. The structural integrity of the AlxCr1 xN/(AlxCr1 x)2O3 multilayer coatings consisting of different interface architectures and number of layers increases with an increasing oxide nitride interface volume fraction up to ~1200 degC. The typically observed two step dissociation process of AlxCr1 xN (to form Cr2N and finally Cr under N2 release) is reduced to a delayed one step dissociation process. We could thus show, that combining AlxCr1 xN nitride coatings with (AlxCr1 x)2O3 is a promising approach in improving their thermal stability.
author_names: R Raab

Christian Martin Koller

Szilard Kolozsvari

Jurgen Ramm

Paul H Mayrhofer
title: Thermal stability of arc evaporated Al Cr O and Al Cr O/Al Cr N multilayer coatings
year: 2018