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Preparation and characterization of nanocrystalline Nd-YAG powder
Materials Letters 61 (2007) 921 – 924 www.elsevier.com/locate/matlet
Preparation and characterization of nanocrystalline Nd-YAG powder Rashmi Singh ⁎, R.K. Khardekar, Arun Kumar, D.K Kohli Target Laboratory, Raja Ramanna Centre for Advanced Technology, PO CAT, Indore, Madhya Pradesh, 452 013, India Received 4 January 2006; accepted 7 June 2006+ Available online 10 July 2006
Abstract Nanocrystalline materials have assumed notable importance in a wide variety of fields owing to numerous possible applications offered by them. These include transparent ceramics wherein they facilitate synthesis as well as sintering at significantly lower temperatures. We report preparation of nanocrystalline neodymium doped yttrium aluminum garnet (YAG) with an ultimate intent to make transparent Nd-YAG ceramic. The Liquid Mix method employed involves mixing of metal nitrates with excess amounts of citric acid followed by dissolution and polymerization in ethylene glycol to form complex chelates. Amorphous powder obtained by firing of polymeric chelate compound at 400 °C permits formation of nanoparticles of Nd:YAG at as low a crystallization temperature as 920 °C as shown by the thermal analysis. Progressive evolution of well crystallized phase-pure YAG was studied by XRD of amorphous powders subjected to different calcination temperatures. Scanning electron microscopic (SEM) study of the crystalline material shows that particle size ranges between 50 and 100 nm. © 2006 Elsevier B.V. All rights reserved. Keywords: Nanomaterials; Electron microscopy; Powder technology; X-ray techniques
1. Introduction Neodymium doped yttrium aluminum garnet (Nd:YAG) single crystal made by Czochralski method [1] has been the most widely used solid state laser material during the last four decades with a wide variety of applications in medicine, materials processing, military and research. But its fabrication requires expensive equipment and crucible material. Moreover, it is extremely difficult to fabricate large diameter crystals or, dope them with greater than 1% neodymium because of the segregation problem associated with the latter. Interest in polycrystalline ceramics, suitable as a laser host dates back to early seventies of the twentieth century when lasing action was successfully demonstrated with these ceramics [2]. Nd:YAG transparent ceramic has received much attention as laser host material because of its several advantages [3]. These materials enable fabrication of large (150 mm) diameter transparent discs and high power (1.46 kW laser output) Nd: YAG lasers employing such discs have been reported [4]. Ever since lasing action was demonstrated in Nd:YAG transparent ceramic in 1995 there has been a significant spurt in
⁎ Corresponding author. Tel.: +91 0731 2442394. E-mail address: [email protected] (R. Singh). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.06.013
activities relating to low temperature synthesis of fine powder of Nd:YAG and its sintering at the lowest possible temperatures to obtain transparent ceramic. The solid state synthesis of ceramic from their respective oxide powder usually requires extensive mechanical mixing and prolonged heat treatment above 1600 °C [5,6]. The processing conditions do not allow easy control over microstructure grain size in the resulting powder. On the other hand sol-gel method based on molecular precursor allows chemical interactions amongst the initial mixture of precursor species favoring the evolution of solid state structure with atomic level mixing which results in as low as 700 °C crystallization temperatures [7], but the use of alkoxide approach is restricted due to rather intricate synthesis procedures and limited commercial availability of various metal alkoxides. Single phase crystallization temperatures for coprecipitation method [8], self-propagating combustion [9] and precipitation by urea method [10] are 900 °C, 1250 °C and 1200 °C respectively. Nanocrystalline materials have turned into a class of their own in recent times with their properties being quite different from those of the corresponding bulk crystalline materials [11]. Transparent polycrystalline Nd:YAG is considered to be an alternative to single crystal new routes for low-temperature synthesis of nano-sized, pure and homogeneous Nd:YAG powders that continue to be explored by the researchers.
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R. Singh et al. / Materials Letters 61 (2007) 921–924
Fig. 1. TG/DTA curve of the precursor gel (crystallization peak at 920 °C can be clearly seen in the inset region).
We report here a potential and inexpensive method of synthesis of nanocrystalline Nd:YAG powder by Liquid Mix method. This chelate-polymerization method employing citric acid was invented by Pechini more than three decades ago and since then has been used to synthesize a wide variety of ferromagnetic, ferroelectric and other mixed-oxide materials [12]. It uses metal salts or alkoxides and chelating agents to form water soluble polymeric complexes, which can be decomposed to obtain the desired mixed-oxide phase. Here the cations of metal salts or alkoxides are made to react with certain weak acids to form polybasic acid chelates. These chelates undergo polyesterification when heated with a polyhydroxyalcohol to form polymeric gellike compound which has cations uniformly mixed and distributed. Subsequently the gel is charred at 400 °C and calcined to obtain crystalline oxide powder. The most important feature of this method is formation of a mixed metal citric acid complex with a chosen stoichiometric ratio stabilized in a polyester based resin, which probably helps in the formation of phase-pure YAG. Advantages of Liquid Mix method are that nano-sized, homogeneously doped phase-pure mixed-oxide powders can be prepared at relatively low crystallization temperatures.
hooked to Eurotherm 2604 programmer-temperature controller up to 400 °C employing a heating rate of 5 °C/min for 6 h to burn out organics. At 400 °C the material got self-ignited to red-hot condition (∼800 °C) within lumps because of highly exothermic reactions. Nd:YAG precursor obtained after initial firing was calcined for 3 h each at temperatures 600°, 700°, 800° and 950 °C employing heating rate of 5 °C/min. After every step grinding in agate mortar was done. The thermogravimetric–differential thermal analysis (TG– DTA) measurements were performed on dried polymeric gel sample employing SETARAM TGA92. The sample was heated up to 1200 °C in oxygen:argon (1:2) atmosphere at a rate of 5 °C/ min using a platinium–rhodium crucible. Powder X-ray diffraction measurements were performed at room temperature on samples subjected to 600, 700, 800 and 950 °C employing a RIGAKU (Geigerflex) diffractometer operating with Cu–Kα radiation. The infrared spectra of dried gel and that fired at 400 °C were recorded on a FTIR (Perkin Elmer PARAGON 1000). The particle size of the crystalline powder was measured with a scanning electron microscope (Philips XL30CP). Special care was taken in preparing samples for SEM, as the calcination at 950 °C resulted in agglomeration of the powder. Dispersion of the powder in acetone was made by ultrasonically agitating the medium for one hour. Graphite holder was dipped in dispersion medium and then dried. DC sputtering technique was used to coat the samples with a gold film of 50 Å to avoid electrostatic charging during analysis. 3. Results and discussion The mechanism of thermal decomposition and the crystallization temperature of the dried polymeric gel precursor as studied by TG– DTA are shown in the thermal analysis curve depicted in Fig. 1. Sample
2. Experimental The starting materials were yttrium nitrate hexahydrate (Y (NO3)3·6H2O, 99.9%, Aldrich), aluminum nitrate nonahydrate (Al(NO3)3·9H2O, 98.5%, Merck), and neodymium nitrate hexahydrate (Nd(NO3)3·6H2O, 99.9%, Aldrich). The constituent nitrates taken in stoichiometric proportions were independently mixed and ground with excess quantities of citric acid and dissolved in ethylene glycol. Transparent solutions were obtained after heating with constant stirring. The quantity of neodymium nitrate was taken for 3 at.% doping in YAG. All the three transparent solutions were mixed and brought to boiling temperature at 90 °C. Solution turned light yellow and then deep yellow and finally brown black after 3 h. Evaporation of solution initiated poly-condensation (polyesterification reaction) resulting in resinous gel which on further heating dried into sticky brown black lumps. The sticky mass was fired in a resistance muffle furnace
Fig. 2. XRD patterns of the gel heated at 600, 800, and 950 °C.
R. Singh et al. / Materials Letters 61 (2007) 921–924
with starting weight of 80 mg was loaded in TG–DTA crucible. The thermogravimetry curve shows that the mass decreased rapidly below 600 °C due to removal of hydroxyl/ester/carboxylic and other organic groups of the polymeric precursor. The thermal decomposition behavior associated with a very large exothermic peak for the sample as seen in the differential thermal analysis curve is suggestive of an auto-ignited combustion process, arising from highly exothermic reactions. The exothermic peak at 920 °C (blown up view shown in the inset) corresponds to the crystallization of YAG phase. The peak is very small because the mass left after decomposition and removal of carbonaceous matter was very small. Fig. 2 shows the XRD pattern of the YAG powder calcined at 600, 800 and 950 °C. The patterns at 600 °C and 800 °C show that the powder was amorphous with a broad and emerging peak centered around the highest intensity peak of YAG phase. The powder calcined at 950 °C revealed peaks of phase-pure crystalline YAG. The intensity peaks are slightly broadened due to line broadening effect as reported for nano-sized particles [13]. The addition of 3% neodymium, understandably, did not cause any shift in the peak positions or additional new peaks due to neodymium oxide. Identical XRD patterns have been reported elsewhere [14] for phase-pure crystalline YAG powder. The IR spectra of the dried gel and the powder fired at 400 °C are presented in Fig. 3. The broad band centered around 3411 cm− 1 is due to bonded hydroxyl group stretching frequency of polymeric intra- and intermolecular bonds. Since the starting materials contained significant amounts of hydroxyl groups their signature in the IR spectra was expected. The peak represented by 2926 cm− 1 corresponds to C–H stretching frequencies in hydrocarbon groups. The peak at 1734 cm− 1 is characteristic of carbonyl stretching vibration of aldehydes. Whereas no starting compounds contained aldehyde group their presence in the polymerized gel could be attributed to oxidation of alcoholic group by nitrate ions released by the metal nitrates. Presence of carboxylate
923
Fig. 4. SEM photograph of Nd-YAG powder obtained after calcination at 950 °C for 6 h (bright spots are particles).
anion –COO– group is confirmed by twin bands at 1586 and 1406 cm− 1 which correspond to antisymmetrical and symmetrical vibrations of – COO– group. Peak at 1078 cm− 1 is due to primary –OH bending. We observe a peak at 879 cm− 1 representing peroxide linkage which can be attributed to the oxidative reactions of carboxylic acidic groups present. A broad peak at 605 cm− 1 represents the characteristic metal-oxygen vibrations. Slight shift in some of the characteristic frequencies is due to polymeric bonding with heavy metals [15]. Scanning Electron Micrograph of the powder derived after calcinations at 950 °C is seen in Fig. 4. Particles are seen as bright spots typically of sizes between 50 and 100 nm on graphite substrate. Particles are scattered and located far from each other with near absence of agglomerates due to special care taken during sample preparation.
4. Conclusion The present study demonstrates the potential of Liquid Mix method to yield phase-pure nanocrystalline Nd-YAG powder at a crystallization temperature <1000 °C which is low as compared to the temperature required for solid state and several other methods of synthesis. The method requires inexpensive reagents. Nanocrystalline Nd-YAG powder synthesized by this method can be used for producing highly transparent YAG ceramics at low sintering temperatures in view of the large surface energy associated with nano-sized powder [16]. The only disadvantage of the method appears to be requirement of handling of very large quantities of reagent in comparison to the final mixed-oxide powder generated. The fine and fluffy nature of the powder formation of agglomerates is understandable. Acknowledgement
Fig. 3. FTIR spectra of the Nd-YAG precursor gel and powder fired at 400 °C.
We thank Dr. V.S. Tiwari, Dr. S.M. Gupta and Shri Indranil Bhaumik of Laser Materials Division, CAT, for providing XRD, FTIR and TG–DTA data for our samples. Thanks are also due to Dr. R.V. Nandedkar and Ms. Pragya Tripathi for SEM results.
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R. Singh et al. / Materials Letters 61 (2007) 921–924
References [1] Aleksander Golubovic, Slobodaka Nikolic, Rados Gajic, Stevan Duricand, Andreja Valcic, J. Serb. Chem. Soc. 67 (4) (2002) 291. [2] M. Sekita, H. Haneda, T. Yanagitani, S. Shirasaki, J. Appl. Phys. 67 (1) (1990) 453. [3] Jianren Lu, Mahendra Prabhu, Jianqlu Xu, Kenichi Ueda, Hideki Yagi, Takakimi Yanagitani, A.A Kaminskii, Appl. Phys. Lett. 77 (23) (2000) 3707. [4] Jianren Lu, T. Murai, K. Takaichi, T. Uematsu, K. Misawa, M. Prabhu, J. Xu, K. Ueda, H. Yagi, T. Yanagitani, A.A. Kaminskii, A. Kudryashov, Appl. Phys. Lett. 78 (23) (2001) 3586. [5] A. Ikesue, K. Kamata, K. Yoshida, J. Am. Ceram. Soc. 78 (1995) 2545. [6] J.M. Yang, S.M. Jeng, S. Chang, J. Am. Ceram. Soc. 79 (1996) 1218. [7] Michael Veith, Sanjay Mathur, Aivaras Kareiva, Mohammad Jilavi, Michael Zimmer, Volker Huch, J. Mater. Chem. 9 (1999) 3069. [8] M. Yada, M. Ohya, M. Machida, T. Kijima, Chem. Commun. (1998) 1941.
[9] E. Akin, H. Der, A.C. Tas III, Ceram. Congress 2 (1996) 440. [10] Naoya Matsushita, Noriyoshi Tsuchiya, Katsuto Nakatsuka, J. Am. Ceram. Soc. 82 (8) (1999) 1977. [11] Peter J. Dobson, Commercial and Industrial Applications for Microengineering and Nanotechnology, London, 1999. [12] C. Jeffrey Brinker, David E. Clark, Donald R. Ulrich, Better Ceramics Through Chemistry II, MRS, Pittsburg, 1989, p. 571. [13] Gregory S. Rohrer, Structure and Bonding in Crystalline Materials, Cambridge, 2001, p. 212. [14] Byung-Joo Chung, Joon-Young Park, Soo-Man Sim, J. Ceram Process. Res. 4 (3) (2003) 1. [15] L.J. Bellamy, The Infrared Spectra of Complex Molecules, Vol. 1 and 2, 3rd ed.Chapman and Hall, Cambridge, 1975. [16] Lei Wen, Xudong Sun, Zhimeng Xiu, Shaowei Chen, Chi-Tay Tsai, J. Eur. Ceram. Soc. 24 (9) (2004) 2681–2688.
Preparation and characterization of nanocrystalline Nd-YAG powder Rashmi Singh ⁎, R.K. Khardekar, Arun Kumar, D.K Kohli Target Laboratory, Raja Ramanna Centre for Advanced Technology, PO CAT, Indore, Madhya Pradesh, 452 013, India Received 4 January 2006; accepted 7 June 2006+ Available online 10 July 2006
Abstract Nanocrystalline materials have assumed notable importance in a wide variety of fields owing to numerous possible applications offered by them. These include transparent ceramics wherein they facilitate synthesis as well as sintering at significantly lower temperatures. We report preparation of nanocrystalline neodymium doped yttrium aluminum garnet (YAG) with an ultimate intent to make transparent Nd-YAG ceramic. The Liquid Mix method employed involves mixing of metal nitrates with excess amounts of citric acid followed by dissolution and polymerization in ethylene glycol to form complex chelates. Amorphous powder obtained by firing of polymeric chelate compound at 400 °C permits formation of nanoparticles of Nd:YAG at as low a crystallization temperature as 920 °C as shown by the thermal analysis. Progressive evolution of well crystallized phase-pure YAG was studied by XRD of amorphous powders subjected to different calcination temperatures. Scanning electron microscopic (SEM) study of the crystalline material shows that particle size ranges between 50 and 100 nm. © 2006 Elsevier B.V. All rights reserved. Keywords: Nanomaterials; Electron microscopy; Powder technology; X-ray techniques
1. Introduction Neodymium doped yttrium aluminum garnet (Nd:YAG) single crystal made by Czochralski method [1] has been the most widely used solid state laser material during the last four decades with a wide variety of applications in medicine, materials processing, military and research. But its fabrication requires expensive equipment and crucible material. Moreover, it is extremely difficult to fabricate large diameter crystals or, dope them with greater than 1% neodymium because of the segregation problem associated with the latter. Interest in polycrystalline ceramics, suitable as a laser host dates back to early seventies of the twentieth century when lasing action was successfully demonstrated with these ceramics [2]. Nd:YAG transparent ceramic has received much attention as laser host material because of its several advantages [3]. These materials enable fabrication of large (150 mm) diameter transparent discs and high power (1.46 kW laser output) Nd: YAG lasers employing such discs have been reported [4]. Ever since lasing action was demonstrated in Nd:YAG transparent ceramic in 1995 there has been a significant spurt in
⁎ Corresponding author. Tel.: +91 0731 2442394. E-mail address: [email protected] (R. Singh). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.06.013
activities relating to low temperature synthesis of fine powder of Nd:YAG and its sintering at the lowest possible temperatures to obtain transparent ceramic. The solid state synthesis of ceramic from their respective oxide powder usually requires extensive mechanical mixing and prolonged heat treatment above 1600 °C [5,6]. The processing conditions do not allow easy control over microstructure grain size in the resulting powder. On the other hand sol-gel method based on molecular precursor allows chemical interactions amongst the initial mixture of precursor species favoring the evolution of solid state structure with atomic level mixing which results in as low as 700 °C crystallization temperatures [7], but the use of alkoxide approach is restricted due to rather intricate synthesis procedures and limited commercial availability of various metal alkoxides. Single phase crystallization temperatures for coprecipitation method [8], self-propagating combustion [9] and precipitation by urea method [10] are 900 °C, 1250 °C and 1200 °C respectively. Nanocrystalline materials have turned into a class of their own in recent times with their properties being quite different from those of the corresponding bulk crystalline materials [11]. Transparent polycrystalline Nd:YAG is considered to be an alternative to single crystal new routes for low-temperature synthesis of nano-sized, pure and homogeneous Nd:YAG powders that continue to be explored by the researchers.
922
R. Singh et al. / Materials Letters 61 (2007) 921–924
Fig. 1. TG/DTA curve of the precursor gel (crystallization peak at 920 °C can be clearly seen in the inset region).
We report here a potential and inexpensive method of synthesis of nanocrystalline Nd:YAG powder by Liquid Mix method. This chelate-polymerization method employing citric acid was invented by Pechini more than three decades ago and since then has been used to synthesize a wide variety of ferromagnetic, ferroelectric and other mixed-oxide materials [12]. It uses metal salts or alkoxides and chelating agents to form water soluble polymeric complexes, which can be decomposed to obtain the desired mixed-oxide phase. Here the cations of metal salts or alkoxides are made to react with certain weak acids to form polybasic acid chelates. These chelates undergo polyesterification when heated with a polyhydroxyalcohol to form polymeric gellike compound which has cations uniformly mixed and distributed. Subsequently the gel is charred at 400 °C and calcined to obtain crystalline oxide powder. The most important feature of this method is formation of a mixed metal citric acid complex with a chosen stoichiometric ratio stabilized in a polyester based resin, which probably helps in the formation of phase-pure YAG. Advantages of Liquid Mix method are that nano-sized, homogeneously doped phase-pure mixed-oxide powders can be prepared at relatively low crystallization temperatures.
hooked to Eurotherm 2604 programmer-temperature controller up to 400 °C employing a heating rate of 5 °C/min for 6 h to burn out organics. At 400 °C the material got self-ignited to red-hot condition (∼800 °C) within lumps because of highly exothermic reactions. Nd:YAG precursor obtained after initial firing was calcined for 3 h each at temperatures 600°, 700°, 800° and 950 °C employing heating rate of 5 °C/min. After every step grinding in agate mortar was done. The thermogravimetric–differential thermal analysis (TG– DTA) measurements were performed on dried polymeric gel sample employing SETARAM TGA92. The sample was heated up to 1200 °C in oxygen:argon (1:2) atmosphere at a rate of 5 °C/ min using a platinium–rhodium crucible. Powder X-ray diffraction measurements were performed at room temperature on samples subjected to 600, 700, 800 and 950 °C employing a RIGAKU (Geigerflex) diffractometer operating with Cu–Kα radiation. The infrared spectra of dried gel and that fired at 400 °C were recorded on a FTIR (Perkin Elmer PARAGON 1000). The particle size of the crystalline powder was measured with a scanning electron microscope (Philips XL30CP). Special care was taken in preparing samples for SEM, as the calcination at 950 °C resulted in agglomeration of the powder. Dispersion of the powder in acetone was made by ultrasonically agitating the medium for one hour. Graphite holder was dipped in dispersion medium and then dried. DC sputtering technique was used to coat the samples with a gold film of 50 Å to avoid electrostatic charging during analysis. 3. Results and discussion The mechanism of thermal decomposition and the crystallization temperature of the dried polymeric gel precursor as studied by TG– DTA are shown in the thermal analysis curve depicted in Fig. 1. Sample
2. Experimental The starting materials were yttrium nitrate hexahydrate (Y (NO3)3·6H2O, 99.9%, Aldrich), aluminum nitrate nonahydrate (Al(NO3)3·9H2O, 98.5%, Merck), and neodymium nitrate hexahydrate (Nd(NO3)3·6H2O, 99.9%, Aldrich). The constituent nitrates taken in stoichiometric proportions were independently mixed and ground with excess quantities of citric acid and dissolved in ethylene glycol. Transparent solutions were obtained after heating with constant stirring. The quantity of neodymium nitrate was taken for 3 at.% doping in YAG. All the three transparent solutions were mixed and brought to boiling temperature at 90 °C. Solution turned light yellow and then deep yellow and finally brown black after 3 h. Evaporation of solution initiated poly-condensation (polyesterification reaction) resulting in resinous gel which on further heating dried into sticky brown black lumps. The sticky mass was fired in a resistance muffle furnace
Fig. 2. XRD patterns of the gel heated at 600, 800, and 950 °C.
R. Singh et al. / Materials Letters 61 (2007) 921–924
with starting weight of 80 mg was loaded in TG–DTA crucible. The thermogravimetry curve shows that the mass decreased rapidly below 600 °C due to removal of hydroxyl/ester/carboxylic and other organic groups of the polymeric precursor. The thermal decomposition behavior associated with a very large exothermic peak for the sample as seen in the differential thermal analysis curve is suggestive of an auto-ignited combustion process, arising from highly exothermic reactions. The exothermic peak at 920 °C (blown up view shown in the inset) corresponds to the crystallization of YAG phase. The peak is very small because the mass left after decomposition and removal of carbonaceous matter was very small. Fig. 2 shows the XRD pattern of the YAG powder calcined at 600, 800 and 950 °C. The patterns at 600 °C and 800 °C show that the powder was amorphous with a broad and emerging peak centered around the highest intensity peak of YAG phase. The powder calcined at 950 °C revealed peaks of phase-pure crystalline YAG. The intensity peaks are slightly broadened due to line broadening effect as reported for nano-sized particles [13]. The addition of 3% neodymium, understandably, did not cause any shift in the peak positions or additional new peaks due to neodymium oxide. Identical XRD patterns have been reported elsewhere [14] for phase-pure crystalline YAG powder. The IR spectra of the dried gel and the powder fired at 400 °C are presented in Fig. 3. The broad band centered around 3411 cm− 1 is due to bonded hydroxyl group stretching frequency of polymeric intra- and intermolecular bonds. Since the starting materials contained significant amounts of hydroxyl groups their signature in the IR spectra was expected. The peak represented by 2926 cm− 1 corresponds to C–H stretching frequencies in hydrocarbon groups. The peak at 1734 cm− 1 is characteristic of carbonyl stretching vibration of aldehydes. Whereas no starting compounds contained aldehyde group their presence in the polymerized gel could be attributed to oxidation of alcoholic group by nitrate ions released by the metal nitrates. Presence of carboxylate
923
Fig. 4. SEM photograph of Nd-YAG powder obtained after calcination at 950 °C for 6 h (bright spots are particles).
anion –COO– group is confirmed by twin bands at 1586 and 1406 cm− 1 which correspond to antisymmetrical and symmetrical vibrations of – COO– group. Peak at 1078 cm− 1 is due to primary –OH bending. We observe a peak at 879 cm− 1 representing peroxide linkage which can be attributed to the oxidative reactions of carboxylic acidic groups present. A broad peak at 605 cm− 1 represents the characteristic metal-oxygen vibrations. Slight shift in some of the characteristic frequencies is due to polymeric bonding with heavy metals [15]. Scanning Electron Micrograph of the powder derived after calcinations at 950 °C is seen in Fig. 4. Particles are seen as bright spots typically of sizes between 50 and 100 nm on graphite substrate. Particles are scattered and located far from each other with near absence of agglomerates due to special care taken during sample preparation.
4. Conclusion The present study demonstrates the potential of Liquid Mix method to yield phase-pure nanocrystalline Nd-YAG powder at a crystallization temperature <1000 °C which is low as compared to the temperature required for solid state and several other methods of synthesis. The method requires inexpensive reagents. Nanocrystalline Nd-YAG powder synthesized by this method can be used for producing highly transparent YAG ceramics at low sintering temperatures in view of the large surface energy associated with nano-sized powder [16]. The only disadvantage of the method appears to be requirement of handling of very large quantities of reagent in comparison to the final mixed-oxide powder generated. The fine and fluffy nature of the powder formation of agglomerates is understandable. Acknowledgement
Fig. 3. FTIR spectra of the Nd-YAG precursor gel and powder fired at 400 °C.
We thank Dr. V.S. Tiwari, Dr. S.M. Gupta and Shri Indranil Bhaumik of Laser Materials Division, CAT, for providing XRD, FTIR and TG–DTA data for our samples. Thanks are also due to Dr. R.V. Nandedkar and Ms. Pragya Tripathi for SEM results.
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R. Singh et al. / Materials Letters 61 (2007) 921–924
References [1] Aleksander Golubovic, Slobodaka Nikolic, Rados Gajic, Stevan Duricand, Andreja Valcic, J. Serb. Chem. Soc. 67 (4) (2002) 291. [2] M. Sekita, H. Haneda, T. Yanagitani, S. Shirasaki, J. Appl. Phys. 67 (1) (1990) 453. [3] Jianren Lu, Mahendra Prabhu, Jianqlu Xu, Kenichi Ueda, Hideki Yagi, Takakimi Yanagitani, A.A Kaminskii, Appl. Phys. Lett. 77 (23) (2000) 3707. [4] Jianren Lu, T. Murai, K. Takaichi, T. Uematsu, K. Misawa, M. Prabhu, J. Xu, K. Ueda, H. Yagi, T. Yanagitani, A.A. Kaminskii, A. Kudryashov, Appl. Phys. Lett. 78 (23) (2001) 3586. [5] A. Ikesue, K. Kamata, K. Yoshida, J. Am. Ceram. Soc. 78 (1995) 2545. [6] J.M. Yang, S.M. Jeng, S. Chang, J. Am. Ceram. Soc. 79 (1996) 1218. [7] Michael Veith, Sanjay Mathur, Aivaras Kareiva, Mohammad Jilavi, Michael Zimmer, Volker Huch, J. Mater. Chem. 9 (1999) 3069. [8] M. Yada, M. Ohya, M. Machida, T. Kijima, Chem. Commun. (1998) 1941.
[9] E. Akin, H. Der, A.C. Tas III, Ceram. Congress 2 (1996) 440. [10] Naoya Matsushita, Noriyoshi Tsuchiya, Katsuto Nakatsuka, J. Am. Ceram. Soc. 82 (8) (1999) 1977. [11] Peter J. Dobson, Commercial and Industrial Applications for Microengineering and Nanotechnology, London, 1999. [12] C. Jeffrey Brinker, David E. Clark, Donald R. Ulrich, Better Ceramics Through Chemistry II, MRS, Pittsburg, 1989, p. 571. [13] Gregory S. Rohrer, Structure and Bonding in Crystalline Materials, Cambridge, 2001, p. 212. [14] Byung-Joo Chung, Joon-Young Park, Soo-Man Sim, J. Ceram Process. Res. 4 (3) (2003) 1. [15] L.J. Bellamy, The Infrared Spectra of Complex Molecules, Vol. 1 and 2, 3rd ed.Chapman and Hall, Cambridge, 1975. [16] Lei Wen, Xudong Sun, Zhimeng Xiu, Shaowei Chen, Chi-Tay Tsai, J. Eur. Ceram. Soc. 24 (9) (2004) 2681–2688.