Ashamanjari, K G

Gopalakrishna, G S

Mahesh, M J

IACS Institutional Repository

 ^Indian J. Phys. 79 (1), 37-40 (2005)< U P%Hydrothermal synthesis and characterization of cobalt (III) hydrated pyrophosphate crystals: 2 (CoHP2 0 7 )M J M ahesh*, G S GopalakrishniiiK G Ashamanjan and J Shashidhara Prasad'Ucpartmcm of Studies in Cie^logy, Vlmveisily of Mysore. M ysorc-570 006. India ‘Department oi Studies in Physicsj University o f Mysore. M ysore-570 006, IndiaE-mail . gopalaki ish20046f^yahoo comKvrcivvd  ? M an h 2004, (wrejned 12 Octfther 2004A bstract 2(f"oIIP/>2> crystals were synthesi/ed  by hydrotlierrnal teehnu|ue in the form o f  single crystals and chaiacteri/.cd by DTA, FTIR andX ray diffraction method 2(C oH P.,0,) crystals crystallized in monoclinic systems with cell paiametcr ol a ~ 6 1600, h = 12.6764, r = 9 .6868  A, a ^ Y  -  . P = 106 7705", v == 1077 (X> (15) with space group P2/6', and paramagnetic nature. Solubility studies indicate that this compound showsp o s i t i v e  coefficient o f solubility.K eyw ords : Hydrothermal synthesis, pyrophosphates, ETIR. magnetism and solubility.PACS N os. 81 lO.Dn, 61 10.N z, 81 7 0 .Pg, 78 30 Hv1. IntroductkmPhosphates were studied extensively owing to there wide range ol applications such as piezoelectric, luminescence, ceramics, superionics, magnetic, etc (1-51. Subsequently, there arc also reports on pyrophosphates exh ib iting  sim ple fram ew ork structure with relatively high ionic conductivity values j6,7]. These pyrophosphates are much easier to obtain in the lorm ol single crystals by hydrothermal techniques. Here, we report a new group o f polym erized pyrophosphate, which exhibits framework type of structure with paramagnetic nature at ambient condition.2. Experimental2 (CoHp2 0 .y) crystals were synthesized by the hydrothermal processing. The growth o f  phosphates by the hydrothermal technique is quite complicated, because o f high corrosive and volatile nature o f phosphorus at elevated tem perature [8]. Adopting earlier methods, the present experiments were carried out in Morey type autoclaves provided with Teflon liners (Figure1), at the temperature range of 230 — 265°C and pressure of 60- 100 bars respectively [9]. All reagents used in the synthesis process were o f Analar grade with 99.9 % purity from Merck.* Corresponding AuthorDesired quantity of CoC ^ was dissolved in of 85% andwas taken in Teflon liners. The cry.stallization was carried out by spontaneous nuc lea lion  co n tro lled  th rough a slow  and program m ed rate o f  heating . The au tho rs w ere ab le  toCAPPLUNGER CAPSPRINGWASHERTEFLON LINER CAPTEFLON LINERAUTOCLAVE BODY  RUPTURE DISCLOWER PLUNGERFigure 1. Schematic diagram of Morey type autoclave.© 2005IA CS38 M  J  M ahesti, G S  G opa lakhshna , K G A sham anjari a n d  J  Shash idhara  P rasadsy n th es ized  2 (C oH P 3 0 7 > c ry s ta ls  u n d e r the fo llo w in g  experimental conditions:Molar ratio -C o^O : P2O 3 : H^O 1 - 1.5: 1 0 - 12: 8 -- 10 T= 260«C; P = 80 bars; Duration= 8 days.The  following reactions could explain the formation o f 2 (CoHp207);2 C0CI3 + 2 H 3PO 4 -^C o^C P O ^). +6HC1, (1)C o .(P O 4 >2 + 2 H 3PO 4 2 (C oHP2 0 7  ) + H .O  (2)On the whole, 2 (C oH P.0 7 ) crystals obtained were (if good quality and exhibit well-developed morphology with smcx)th surface, pink colour and translucent luster. The size of the crystals is 0.5 to 3 mm (Figure 2). The growth along the basal planes is much faster than along the other faces.optimize the growth tem perature o f the studied compound (250 -260^).300817/384, 670/288 x~163 y-186  Scale Micron/PixelF igure 2. Photograph o f  2(C oH P207) cry.slal and schem atic diagram. Solubility study :Solubility study is an im potent param eter for the successful growth of phosphates in the form o f single crystals. The lack of systematic studies of solubility data was responsible for the earlier failures in the growth o f  phosphates by hydrothermal methods 110]. Chengqian Zhang et al attributed that based on the solubility results o f a com pound it is possible to optimize the growth conditions [11]. The solubility measurem ents were carried out by weight loss m ethod to understand the growth process and to optimize the growth conditions. Here, a crystal is kept in equilibrium at the desired pressure and temperature conditions for a known period in various normality o f H^PO^ solution. The solvent - solute interaction has been studied in detail with reference to the temperature and normality o f H3PO4. The results indicate positive correlation o f  solubility with both normality and temperature ranging from 0.085 to 0 .125gl-lT -1. H owever, m aximum percent o f  so lubility  observed at the temperature range o f 250-275^C in various normality o f H 3PO 4 solutions (Figure 3). Based on these results, it was possible toTemperature T®CF ig u r e  3 . S o lu b ility  cu rve o f  2 (C o H p 2 0 .^ ) com pound  and hrslogram.FTIR spectroscopy:FTIR spectrum recorded by a high resolution Perkin Elmer Infrared Spectrophotom eter in the range o f 4000- 400 cm''* (Figure 4). This com pound exhibits number of prominent fine and splitting absorption bands especially in the four frequency regions i.e. at = 3330 cm~*, Vj = 2144 -16(X)cm'*, V3 = 1165- 930cm “  ^ and = 723 -  480 cm~* regions. The most interesting feature o f this spectrum  is the presence o f H-O-H molecule, which is clearly depicted in the region 3330 cm"*. The vibrational band at 2144 -1 6 0 0  cm"* is due to the presence of cobalt bearing molecules. H igher the degree o f condensation, there will be higher degree o f com plexity and splitting in the IR spectra of phosphates [ 12]. Vibrations at 1165 -  930cm ”* and 723 — 480 cm ”* regions exhibit fineness and m ultiple splitting, which clearly indicate the stretching o f P  -  O -  P molecules and the condensation o f [POJ-^' tetrahedra to [P2O 7].H ydro therm a l syn thesis and  characterization  etc 391/cmF ig u re  4 . F'^ TIR spectrum  o f  2(CoHP^0 7 ) compoundD i f f e r e n t i a l  t h e r m a l  a n a l y s i s  :The DTA curve was recorded using DTA/ETA instrum ent (Model 021 NAL India) from room tem perature to 600%^ The results yielded multiple endothermic peaks (Figure 5). The peak at 128^^ is due to liberation of water m olecule and the peak at 235"C is due to the chem ical diffusion. Subsequently, the compound started melting at 4 0 0 ^  and clearly indicates low therm al s ta b ility  c o m p ared  to  the  d e r iv a tiv e  o f  alkali pyrophosphates reported earlier |9J.6). The polymerization o f phosphates with Co has made as to reveal its coordinates and packing mode. Each Co atom has coordinates with six pyrophosphate oxygen atoms that is, from two O- atoms o f one terminal pyrophosphate. Detailed structure IS discussed elsewhere [13].Figure 5. DTA curve of 2(CoHF^207) com pound X-ray d iffraction:The X- ray diffraction study was carried out for single crystal ot 2 (CoH P207>. The m easurem ents were made on a DIPLabo Imaging Plate system with graphite m onochromatered radiation (M oKct). Thirty-six sets o f data were collected by oscillation method. The com pound crystallized in monocHnic system and space group is P2^/C^ with cell param eters o f a — 9 .1609, b = 12.6764, c = 9.6868 A, a  = /  = 90®, = 106.7705^’and v= 1077.06(15) A^. Structure was solved using SHELEX 97. The statistical weight factor was also included in the last cycle of refinement. ORTEP of the molecule with 50% probability is shown in (FigureFigure 6. ORTEP diagram o f  2(CoHP20 .y) m olecules at 50% probability. Magnetic property :Magnetic susceptibility m easurem ents are made using G ouy's balance by applying field strength o f 0.5 — 2.5 K Gauss at 3(X)K. Magnetic moments o f cobalt bearing com pounds fall in two broad clashes. First, those are having essentially tem perature - independent magnetic m om ents due to m ononuclear com plexes having interaction between the unpaired electrons on different cobalt ions in the range o f 4.3 — 5.2 BM . The second in which the m om ents arc tem perature  dependent. T he p relim inary  investigation o f the com pound exhibits m agnetic m om ents in4 0AcknowledgmentsM  J  M ahesh, G  S  G opalakrishna, K  G A sham an jari a n d  J  Shash idhara  P rasadthe range from 2.79 -  3.98 BM (Figure 7) indicating paramagnetic nature. However, the value.s are relatively  low er than the cobalt derivatives. Detailed investigations will be discussed elsewhere4 2  -  4 1 -  4 0  3 9  - 3 8 -3.73 6 - 3 5 -  3 4  - 3 3 3 2  3 1 H 3 0 2 9  -2.8 -  2 7  - 2 6  - 2 5 - 2 405 1 0 1 5 2 0Fteld Strength (K gauss)2 5F ig u re  7. Magnetic moment oi 2(CoHP,0.^) compound3. Conclusion2 (CoHP.>0 7 ) crystals were synthesized by hydrothermal method in the form of single crystals with well-developed morphology. Solubility studies indicate that this com pound shows positive coefficient o f solubility. Single crystal X-ray studies revealed that this com pound crystallized in m onoclim c system  with framework structure. Prelim inary m agnetic results indicate that to be a paramagnetic.The authors would like to express thanks to the Department ot Science and Technology, G overnm ent o f India for financial assistance under the project SP/S2/M -44/96-97.R e fe re n c e s[ I ]  H Y P  Hong Mater. Hvs tiuU. 11 173 (1976)[21 H P  Weber, T  C  Dmen. H G Daniel Meyer and B C Tofield Appi r/iy.s. U t t .  22 534 (1973)(3J S Yamanaku. K Yoshioka and M Hatton S o lid  S ta te  lo n irs  40 4^ ' (1990)|4J T Ohuzuka, M Kitagawa and T Hirai J  Llertrorheni.  Sor, 137 760 (1990)[5J M Forsyth, S Wong, K M Naiin, A S Bcsi. P J Neman and D K' M acFarlane Sol. State lontrs  124 213 (1999)6] K Benkhouja, M Zuhir, A Sadel, A Handi^ci, A Boukhari, F: M Holt, J Aricie and M Drillon Mater. Re\ Bull. 30 49 (1995)|7 j  N K L o k an a th , M A S rid h ar, .1 Shash idhara  Prasad , (i S Gopalakrishna and K Ci Ashamanjari J  Mater Set I.ett 18 177  ^(1 9 9 9 )[8] K Byrappa, G S G opalakrishna, V V enkatachalapathy aiul l‘. Puttaraiu 7 Mater Sir  20 1419(1985)19] M Mahendra, S V* Madhu, B H Doreswamy, G S Gopalakrishna M A Sridhar, .1 Sha.shidhara Piasad and K G Ashamanian Mater  76 > Bull. 38 1309 (2003)[10] K Byrappa. G S Gopalakrishna and B V Umeshdiilta .7 Mau i Sei  27 4439 (1992)[ 11 ] Zhang Chengqian, Wang Jiyang, Hu Xiaobo, Jiang Huaidong, lau Yaogang and Ghuangtian Chen ,7 Crystal Cjrowth 235 1 (2007 >[12] K Byrappa, I I Plyysnina and G I Dorokhova J. M ate r  Set 17 1847 (1982)[13) G S Gopalakrishna, M Mahendra, M J Mahesh, B H Doreswaim M A S rid h ar and J .Sha.shidhara P rasad  .7 A n a l  Set  20 (>' (2004)

Hydrothermal Synthesis and Characterization of Cobalt (III) Hydrated Pyrophosphate Crystals : 2(CoHP2O7)

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Hydrothermal Synthesis and Characterization of Cobalt (III) Hydrated Pyrophosphate Crystals : 2(CoHP2O7)

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