TY  - CONF
AU  - Vojisavljević, Katarina
AU  - Malic, Barbara
AU  - Mamoru, Senna
AU  - Drnovšek, Silvo
AU  - Kosec, Marija
PY  - 2013
UR  - http://rimsi.imsi.bg.ac.rs/handle/123456789/2916
AB  - Recently, a considerable effort has been devoted to research and development of n- and p-type transparent conducting oxides (TCO), where the improvement of their properties will give an added impetus in the field of invisible electronics for production of different optoelectronic devices. Due to the lack of p-type oxide semiconductors, with high enough conductivity and transparency across the visible spectrum, special attention has been paid to synthesis of p-type delafossite CuMO2 (M = Al, Cr or Y) materials. Copper aluminate (CuAlO2) thin films prepared by physical vapour deposition from multicomponent sputtering targets exhibit the p-type behaviour and have already been used in various applications in optoelectronics. Besides, the CuAlO2 can be used as a catalyst for the conversion of solar power to hydrogen energy, thermoelectric converter or ozone sensor.
The first step in production of high quality sputtering targets is related to preparation of phase pure powders and dense ceramics.A delafossite CuAlO2 has been usually prepared by conventional solid state synthesis from CuO or Cu2O and Al2O3 powders, where milling in different liquid media with long milling times were at first used to achieve homogeneous reagent mixtures, and then multiple calcinations at high temperatures with intermediate wet-milling steps were applied. However, secondary phases and low relative densities are yet to be improved for the solid-state synthesized delafossite CuAlO2, even when high processing temperatures (1200 – 1350 oC) and extremely long periods have been used. 
The main idea of this work was to promote the reaction of the delafossite CuAlO2 formation during solid state synthesis by changing the usually used Al2O3 with more reactive Al- compounds, such as boehmite (AlOOH). Its exothermic decomposition at low temperatures is expected to improve the conventional solid state synthesis route. The well-mixed powder mixture, consisting of the 1 µm sized Cu2O particles fully covered with fine nano-boehmite rod-like particles, and decomposition of the nano-boehmite powder upon heating have contributed to acceleration of the inherently slow solid state reaction during the double calcination of the powder mixture for 10 h at 1100 oC. The secondary spinel-CuAl2O4 phase has been avoided by calcining the powder mixture in argon atmosphere, where the oxidation of cuprous ions has been precluded. A short sintering time of 2 h at 1100 oC in air atmosphere was essential to obtain single phase CuAlO2 ceramic with 86 % of theoretical density. According to EDXS, traces of Cu-rich impurities were identified only at the surface of the pellet, while the bulk of the sample remained as a single phase delafossite with uniformly distributed porosity. The semiconducting nature of the ceramic sample was confirmed by the temperature dependent dielectric parameters measurements (ε’ and tgδ) in the 10 kHz-1MHz frequency range between 297 and 473 K.
PB  - ECERS, 2013
C3  - Conference of the European Ceramic Society XIII
T1  - Solid state synthesis of CuAlO2: From a nano-boehmite - cuprous oxide powder mixture to the single phase ceramics
EP  - 77
SP  - 77
UR  - https://hdl.handle.net/21.15107/rcub_rimsi_2916
ER  - 

@conference{
author = "Vojisavljević, Katarina and Malic, Barbara and Mamoru, Senna and Drnovšek, Silvo and Kosec, Marija",
year = "2013",
abstract = "Recently, a considerable effort has been devoted to research and development of n- and p-type transparent conducting oxides (TCO), where the improvement of their properties will give an added impetus in the field of invisible electronics for production of different optoelectronic devices. Due to the lack of p-type oxide semiconductors, with high enough conductivity and transparency across the visible spectrum, special attention has been paid to synthesis of p-type delafossite CuMO2 (M = Al, Cr or Y) materials. Copper aluminate (CuAlO2) thin films prepared by physical vapour deposition from multicomponent sputtering targets exhibit the p-type behaviour and have already been used in various applications in optoelectronics. Besides, the CuAlO2 can be used as a catalyst for the conversion of solar power to hydrogen energy, thermoelectric converter or ozone sensor.
The first step in production of high quality sputtering targets is related to preparation of phase pure powders and dense ceramics.A delafossite CuAlO2 has been usually prepared by conventional solid state synthesis from CuO or Cu2O and Al2O3 powders, where milling in different liquid media with long milling times were at first used to achieve homogeneous reagent mixtures, and then multiple calcinations at high temperatures with intermediate wet-milling steps were applied. However, secondary phases and low relative densities are yet to be improved for the solid-state synthesized delafossite CuAlO2, even when high processing temperatures (1200 – 1350 oC) and extremely long periods have been used. 
The main idea of this work was to promote the reaction of the delafossite CuAlO2 formation during solid state synthesis by changing the usually used Al2O3 with more reactive Al- compounds, such as boehmite (AlOOH). Its exothermic decomposition at low temperatures is expected to improve the conventional solid state synthesis route. The well-mixed powder mixture, consisting of the 1 µm sized Cu2O particles fully covered with fine nano-boehmite rod-like particles, and decomposition of the nano-boehmite powder upon heating have contributed to acceleration of the inherently slow solid state reaction during the double calcination of the powder mixture for 10 h at 1100 oC. The secondary spinel-CuAl2O4 phase has been avoided by calcining the powder mixture in argon atmosphere, where the oxidation of cuprous ions has been precluded. A short sintering time of 2 h at 1100 oC in air atmosphere was essential to obtain single phase CuAlO2 ceramic with 86 % of theoretical density. According to EDXS, traces of Cu-rich impurities were identified only at the surface of the pellet, while the bulk of the sample remained as a single phase delafossite with uniformly distributed porosity. The semiconducting nature of the ceramic sample was confirmed by the temperature dependent dielectric parameters measurements (ε’ and tgδ) in the 10 kHz-1MHz frequency range between 297 and 473 K.",
publisher = "ECERS, 2013",
journal = "Conference of the European Ceramic Society XIII",
title = "Solid state synthesis of CuAlO2: From a nano-boehmite - cuprous oxide powder mixture to the single phase ceramics",
pages = "77-77",
url = "https://hdl.handle.net/21.15107/rcub_rimsi_2916"
}

Vojisavljević, K., Malic, B., Mamoru, S., Drnovšek, S.,& Kosec, M.. (2013). Solid state synthesis of CuAlO2: From a nano-boehmite - cuprous oxide powder mixture to the single phase ceramics. in Conference of the European Ceramic Society XIII
ECERS, 2013., 77-77.
https://hdl.handle.net/21.15107/rcub_rimsi_2916

Vojisavljević K, Malic B, Mamoru S, Drnovšek S, Kosec M. Solid state synthesis of CuAlO2: From a nano-boehmite - cuprous oxide powder mixture to the single phase ceramics. in Conference of the European Ceramic Society XIII. 2013;:77-77.
https://hdl.handle.net/21.15107/rcub_rimsi_2916 .

Vojisavljević, Katarina, Malic, Barbara, Mamoru, Senna, Drnovšek, Silvo, Kosec, Marija, "Solid state synthesis of CuAlO2: From a nano-boehmite - cuprous oxide powder mixture to the single phase ceramics" in Conference of the European Ceramic Society XIII (2013):77-77,
https://hdl.handle.net/21.15107/rcub_rimsi_2916 .

TY  - CONF
AU  - Vojisavljević, Katarina
AU  - Malič, Barbara
AU  - Mamoru, Senna
AU  - Kuscer, Danjela
AU  - Drnovšek, Silvo
AU  - Kosec, Marija
PY  - 2012
UR  - http://rimsi.imsi.bg.ac.rs/handle/123456789/2918
AB  - In the past two decades, a considerable effort has been devoted to the study and development of different n- and p-type oxide semiconductors for transparent electronics applications. The p-type delafossite materials CuMO2 (M = Al, Cr or Y) with the band gap above 3 eV, which allows high transparency across the entire visible region, are of particular interest. Copper aluminate (CuAlO2) films prepared by physical vapour deposition have been reported to exhibit the p-type behaviour and have already been used in various applications in optoelectronics. Phase-pure targets with a high relative density are prerequisites for physical vapour deposition of high quality CuAlO2 films. However, secondary phases and low relative densities have been reported for the solid-state synthesized delafossite CuAlO2 although high processing temperatures and extremely long times have been used [1, 2].
The aim of this work has been to prepare the phase pure delafossite powders and dense ceramics by solid-state synthesis. Instead of the usually reported α-alumina (α-Al2O3), we introduced the nano-sized boehmite µ-AlOOH.xH2O powder as an aluminium source, for two reasons, i.e., for its high specific surface area and a consequent large number of contacts with Cu2O particles and for higher reactivity as a consequence of the thermal decomposition (Hedvall effect) as compared to the oxide. Furthermore, the role of different atmospheres, namely inert (Ar) and oxidising (air), has been explored. 
The solid-state reaction between nano-Al2O3 and Cu2O (up to ≈ 1 µm in size) at 1100oC in argon resulted in the delafossite phase with appreciable quantities of both unreacted oxides even after 24 h of heating. In contrast, phase pure delafossite powder was synthesized upon heating the nano-boehmite and Cu2O powder mixture for 2 x 10 h at 1100oC in inert Ar atmosphere as confirmed by XRD. The powder consisted of loose agglomerates of plate-like particles of a few 100 nm in size. Heating in air resulted in formation of the spinel CuAl2O4 and CuO phases beside the delafossite in both cases. 
The ceramic with 86% of theoretical density has been obtained after sintering the boehmite-derived CuAlO2 powder compact at 1100oC for 2h in air. According to XRD the ceramic was single-phase delafossite. However SEM /EDXS analysis revealed traces of Cu-rich impurities at the surface of the pellet. The bulk of the sample revealed a dense microstructure with a uniform distribution of porosity within the delafossite matrix.

References
[1] H. G. Zheng, K. Taniguchi, A. Takahashi, Y. Liu, C. N. Xu, Appl. Phys. Lett., 85, 1728 (2004).
[2] Y. -C. Liou, U. -R. Lee, J. Alloys Comp., 467, 496 (2009).

Acknowledgement
We acknowledge for funding the 7.FP ORAMA (NMP2-LA-2010-246334: Oxide materials for electronics applications).
C3  - 4th Symposium on Transparent Conductive Materials, 21-26 October 2012, Crete, Greece
T1  - Processing of delafossite CuAlO2 ceramic targets by solid state synthesis route
UR  - https://hdl.handle.net/21.15107/rcub_rimsi_2918
ER  - 

@conference{
author = "Vojisavljević, Katarina and Malič, Barbara and Mamoru, Senna and Kuscer, Danjela and Drnovšek, Silvo and Kosec, Marija",
year = "2012",
abstract = "In the past two decades, a considerable effort has been devoted to the study and development of different n- and p-type oxide semiconductors for transparent electronics applications. The p-type delafossite materials CuMO2 (M = Al, Cr or Y) with the band gap above 3 eV, which allows high transparency across the entire visible region, are of particular interest. Copper aluminate (CuAlO2) films prepared by physical vapour deposition have been reported to exhibit the p-type behaviour and have already been used in various applications in optoelectronics. Phase-pure targets with a high relative density are prerequisites for physical vapour deposition of high quality CuAlO2 films. However, secondary phases and low relative densities have been reported for the solid-state synthesized delafossite CuAlO2 although high processing temperatures and extremely long times have been used [1, 2].
The aim of this work has been to prepare the phase pure delafossite powders and dense ceramics by solid-state synthesis. Instead of the usually reported α-alumina (α-Al2O3), we introduced the nano-sized boehmite µ-AlOOH.xH2O powder as an aluminium source, for two reasons, i.e., for its high specific surface area and a consequent large number of contacts with Cu2O particles and for higher reactivity as a consequence of the thermal decomposition (Hedvall effect) as compared to the oxide. Furthermore, the role of different atmospheres, namely inert (Ar) and oxidising (air), has been explored. 
The solid-state reaction between nano-Al2O3 and Cu2O (up to ≈ 1 µm in size) at 1100oC in argon resulted in the delafossite phase with appreciable quantities of both unreacted oxides even after 24 h of heating. In contrast, phase pure delafossite powder was synthesized upon heating the nano-boehmite and Cu2O powder mixture for 2 x 10 h at 1100oC in inert Ar atmosphere as confirmed by XRD. The powder consisted of loose agglomerates of plate-like particles of a few 100 nm in size. Heating in air resulted in formation of the spinel CuAl2O4 and CuO phases beside the delafossite in both cases. 
The ceramic with 86% of theoretical density has been obtained after sintering the boehmite-derived CuAlO2 powder compact at 1100oC for 2h in air. According to XRD the ceramic was single-phase delafossite. However SEM /EDXS analysis revealed traces of Cu-rich impurities at the surface of the pellet. The bulk of the sample revealed a dense microstructure with a uniform distribution of porosity within the delafossite matrix.

References
[1] H. G. Zheng, K. Taniguchi, A. Takahashi, Y. Liu, C. N. Xu, Appl. Phys. Lett., 85, 1728 (2004).
[2] Y. -C. Liou, U. -R. Lee, J. Alloys Comp., 467, 496 (2009).

Acknowledgement
We acknowledge for funding the 7.FP ORAMA (NMP2-LA-2010-246334: Oxide materials for electronics applications).",
journal = "4th Symposium on Transparent Conductive Materials, 21-26 October 2012, Crete, Greece",
title = "Processing of delafossite CuAlO2 ceramic targets by solid state synthesis route",
url = "https://hdl.handle.net/21.15107/rcub_rimsi_2918"
}

Vojisavljević, K., Malič, B., Mamoru, S., Kuscer, D., Drnovšek, S.,& Kosec, M.. (2012). Processing of delafossite CuAlO2 ceramic targets by solid state synthesis route. in 4th Symposium on Transparent Conductive Materials, 21-26 October 2012, Crete, Greece.
https://hdl.handle.net/21.15107/rcub_rimsi_2918

Vojisavljević K, Malič B, Mamoru S, Kuscer D, Drnovšek S, Kosec M. Processing of delafossite CuAlO2 ceramic targets by solid state synthesis route. in 4th Symposium on Transparent Conductive Materials, 21-26 October 2012, Crete, Greece. 2012;.
https://hdl.handle.net/21.15107/rcub_rimsi_2918 .

Vojisavljević, Katarina, Malič, Barbara, Mamoru, Senna, Kuscer, Danjela, Drnovšek, Silvo, Kosec, Marija, "Processing of delafossite CuAlO2 ceramic targets by solid state synthesis route" in 4th Symposium on Transparent Conductive Materials, 21-26 October 2012, Crete, Greece (2012),
https://hdl.handle.net/21.15107/rcub_rimsi_2918 .

TY  - CONF
AU  - Vojisavljević, Katarina
AU  - Malič, Barbara
AU  - Mamoru, Senna
AU  - Drnovšek, Silvo
AU  - Kosec, Marija
PY  - 2012
UR  - http://rimsi.imsi.bg.ac.rs/handle/123456789/2910
AB  - Within this work, the focus was on preparation of the delafossite CuAlO2 single phase powder and ceramic with a high density by the solid state synthesis, and on dielectric properties of the as-synthesized ceramic. The reaction between the nanoboehmite γ-AlOOH, with a high specific surface area, and the Cu2O, with the particles below 1 μm, was enhanced by comminution in a high energy mill, which resulted in reduction of the particle size and consequently shorter diffusion paths between constituent powders. The phase pure CuAlO2 powder was synthesized upon heating the reagent powder mixture two times for 10 h at 1100oC in the inert argon atmosphere as confirmed by the X-ray analysis. The ceramic with 86% of theoretical density was obtained after sintering the CuAlO2 powder compact at 1100oC for 2 h in air. According to the X-ray analysis the ceramic sample was single-phase. The bulk of the sample revealed a dense microstructure with a uniform distribution of porosity within the delafossite matrix. However, traces of Cu-rich impurities have been identified at the surface of the pellets by the EDXS analysis. The semiconducting nature of the ceramic sample was confirmed by the temperature dependent dielectric parameters measurements (ε’ and tgδ) in the 10 kHZ-1MHz frequency range between 297 and 473 K.
C3  - 48th International Conference  on Microelectronics, Devices and Materials  with the Workshop on  Ceramic Microsystems
T1  - Preparation and dielectric properties of CuAlO2 ceramics
EP  - 156
SP  - 151
UR  - https://hdl.handle.net/21.15107/rcub_rimsi_2910
ER  - 

@conference{
author = "Vojisavljević, Katarina and Malič, Barbara and Mamoru, Senna and Drnovšek, Silvo and Kosec, Marija",
year = "2012",
abstract = "Within this work, the focus was on preparation of the delafossite CuAlO2 single phase powder and ceramic with a high density by the solid state synthesis, and on dielectric properties of the as-synthesized ceramic. The reaction between the nanoboehmite γ-AlOOH, with a high specific surface area, and the Cu2O, with the particles below 1 μm, was enhanced by comminution in a high energy mill, which resulted in reduction of the particle size and consequently shorter diffusion paths between constituent powders. The phase pure CuAlO2 powder was synthesized upon heating the reagent powder mixture two times for 10 h at 1100oC in the inert argon atmosphere as confirmed by the X-ray analysis. The ceramic with 86% of theoretical density was obtained after sintering the CuAlO2 powder compact at 1100oC for 2 h in air. According to the X-ray analysis the ceramic sample was single-phase. The bulk of the sample revealed a dense microstructure with a uniform distribution of porosity within the delafossite matrix. However, traces of Cu-rich impurities have been identified at the surface of the pellets by the EDXS analysis. The semiconducting nature of the ceramic sample was confirmed by the temperature dependent dielectric parameters measurements (ε’ and tgδ) in the 10 kHZ-1MHz frequency range between 297 and 473 K.",
journal = "48th International Conference  on Microelectronics, Devices and Materials  with the Workshop on  Ceramic Microsystems",
title = "Preparation and dielectric properties of CuAlO2 ceramics",
pages = "156-151",
url = "https://hdl.handle.net/21.15107/rcub_rimsi_2910"
}

Vojisavljević, K., Malič, B., Mamoru, S., Drnovšek, S.,& Kosec, M.. (2012). Preparation and dielectric properties of CuAlO2 ceramics. in 48th International Conference  on Microelectronics, Devices and Materials  with the Workshop on  Ceramic Microsystems, 151-156.
https://hdl.handle.net/21.15107/rcub_rimsi_2910

Vojisavljević K, Malič B, Mamoru S, Drnovšek S, Kosec M. Preparation and dielectric properties of CuAlO2 ceramics. in 48th International Conference  on Microelectronics, Devices and Materials  with the Workshop on  Ceramic Microsystems. 2012;:151-156.
https://hdl.handle.net/21.15107/rcub_rimsi_2910 .

Vojisavljević, Katarina, Malič, Barbara, Mamoru, Senna, Drnovšek, Silvo, Kosec, Marija, "Preparation and dielectric properties of CuAlO2 ceramics" in 48th International Conference  on Microelectronics, Devices and Materials  with the Workshop on  Ceramic Microsystems (2012):151-156,
https://hdl.handle.net/21.15107/rcub_rimsi_2910 .