Byrappa, K

Raj, B Sanjeeva Ravi

IACS Institutional Repository

Indian J. Phvs. 72A (\), 1-10 ( 1W 8)1JP A— .in intcmahoniil lomnalCrystal growth, morphology and properties of NaHMP20 7 (M = Ni, Co, Mn, Z.H, Cd, Pb)K.llyrappa* and B.Sanjeeva Ravi Raj[)cpai Imeiil of Geology, University of Mysore, Manasagangolri Mysore - 570 006, India.Abstract Crystal growth ofNaHMP20 7( M-Ni, Co, Mn, Zn, Cd, Pb) has been carried out by hydrothermal technique The studies concerning the crystal growth processes and the moipliology of these supermini; pyrophosphates with reference to the type of cations, its ionic radii and other thermodynamic charactersilics have been carried out Similarly the impedance spectroscopic properties of these superionic pyrophosphates have been reportedKeywords Crystal growth, morphology, hydrothermal lechinquePACS NO 81 10 Dn1. IntroductionPhosphates ibim an important group of technological materials owing to their wide range of physical and chemical properties The synthesis of phosphates began in the peivious century Super ionic phosphates have been reported for the past 20 years or so Moreover, all the super ionic phosphates reported soon aflei discovery of NAS1CON were all orthophosphates. For the first Mine oni group ieported high ionic conductivity in condensed phosphates, viz , pyrophosphates 11-3] Since then a lot of work is going on in this direction In the present work, the authors have studied the moipliology of these crystals in great deLail, with reference to the type of cation, ionic ladii and thermodynamic characteristics These studies give an insight into the ciystal growth of such superioruc compounds in general Also the impedance spectroscopic properties of these superionic pyrophosphates are given in brief2. Crystal GrowthCrystal growth experiments were carried out under three different PT conditions(i) hydrothermal crystallization under lower pressure and temperature conditions;(ii) hydrothermal crystallization under moderate pressure and temperature conditions, (hi) hydrothermal crystallization under higher pressure and temperature conditionsIn the first case, experiments were carried out in small autoclaves(temperature 100 - 250°(\ pressure 100 - 200 bars ) and smaller Morey autoclaves provided with teflon liners The starting solutions were prepared either by dissolution of PzO, in water or by directly taking I^PO, followed by the addition of respective carbonates or oxides or nitrates or chlorides of respective cations or by the introduction of respective hydroxide into the HjP0 4 in various proportions (maximum filling 70%) The alkaline component of the starting materials was used in the form of a molar solution of a a definite molarity and this solution acts as a mineralizer Since the crystallization occurred by spontaneous nucleation, the temperature of the furnace was slowly increased to control the rate of nucleation The experimental temperature range was 200-300nC and the duration was 7 to 10 days The experimental conditions are given in Table I*Aullinr lor correspondence Iv-mail IJYRONftiKIlASIKiA VSNI. Nil I IN CO 1998 I ACSK Byrappu aid  H Siuiieeva R m  RajT. fcu  I. Expenmenlal condmons for low lemper.lu,e hyjrolh.nn.) q i U t a i « _Compound N M  Compon«,U Tmjp I W  % "  Du^  *  ^[u k n t l  tmincraliiH ( K )  (Mral W ___________________a) H,P04 NaOH CdO Zr(NO,)( (ml) * (ml) (gm) <B">)1)4 S(SM) 1 05 250S 5(5M) 1 05 2506 5(5M) 1 0 5 250n)5 S(2M) 1 0 5 2505 5<3M) 1 0 5 2505 5(4M) 1 05 250s S(SM) 1 05 250s S(ftM) 1 0 5 250s S(7M) 1 05 250III)s 5(SM) 1 0 3 2505 S(SM) 1 04 2505 5(5M) 1 0 5 2505(SM) 1 06 250s S(SM) 1 0 75 2505 S(5M) 1 0Q0 250IV)5 5(5M) 0 5 0 5 2505 5(SM) 0 75 05 2505 5(5M) 1 00 05 2505 5(5M) 1 50 0 5 250bjH.PO, NaOH Co(NO,),Zr(NO,), (ml) (ml) (gm) (gm)1)5 5(5M) 1 03 2505 5(5M) 1 04 2505 5(5M) 1 0.5 2505 5(5 M) 1 06 250ii)5 5(SM) 0 5 0 5 2505 5(5M) 0 75 0 5 2508 2-3 Yellowish grey8 2-5 Yellowish grey8 1-3 Yellowish grey8 dissolved8 crystalline material yellowish grey8 1-3 Yellowish grey8 1-4 Yellowish grey8 1-3 Yellowish grey8 0.5 Yellowish grey8 1-3 Yellowish grey8 1-3 Yellowish grey8 1-6 Yellowish grey8 0.5-2 Yellowish grey8 0.5-1 Yellowish grey8 irregular•8 1-2 Yellowish grey8 1-2 Yellowish grey8 2-5 Yellowish grey8 1-3 Yellowish grey8 0 5-2 pink8 0.5-2 pink8 1-4 pink8 1-3 pink8 1 pink8 1-2 pinkSO 40 70 30SO 40t3 35 t5 35 85 3585 3585 3585 3585 3585 3590 4085 38QO 40 95 4580 3280 3285 3590 4080 3285 3585 3585 3585 3585 35The experiments under moderate PT conditions were carried out by using Morey autoclaves and Tuttle autoclaves within the temperature and pressure range P^ 150-800 bars, T“25Q-400"C using teflon and platinum liners respectively In some experiments the results were much superior compared to the lower PT conditions with regard id  the crystal quality and size.The experiments under higher PT conditions were conducted using Tuttle cold-cone sealed autoclaves provided with platinum liners (T ~700BC and P = I 5 Kbars) The results of these experiments are different The authors obtained compounds without a proton in their composition, like NaKeP20 7, NaCoP20 7 which are isostructural to allaudite,The crystallization processes for the formation of HNaMP20 7 (where M = Ni, Co, Mn, Pb and Cd) crystals have been studied, based on solvent-solute interactions and the complexation processes is described thorough the following reaction series with regard to HNaCdP20 7Crystal growth, morphology and properties etc3NaOH + H ,P04 ->3Cd(N0,)2 + 2H ,P04 ->Zr(NO,)4 + 4NaOH211,1*0, ->NaNO, + H„P,0, ->N a ,P C V  H / , 0 , >Cd,(PO,), t H ,P ,(V  411,0 ->Cd(NO,), + ->NaOll t H,CdP,0,Cd(OH), < NaHjPjO, ->Na3PO; + 3H20C d/P O J, + 3H?0  + 6 N 02 t  43LO] T 4NaN03 + 2H20   ^ Z r0 2 ll,P 20 74 l l 20  NaH3P20 7 4 H N 0 3 NaH,P20 7 4 Na2H P04 H7CdP20 7 + 2H3P 04 + 2C d (0 ll)2 H 2CdP70 7 4 2H N 03 HNaCdP20 7 4 H 20  HNaCdP20 7 + 211^0f lic study of complcxal'.on process with reference to the solvent-solute interaction is of great importance to understand the crystallization of any compound [4] including pyrophosphates Reports of such studies are seldom found in the literature for superionic phosphatesThe crystallization process involving many chemical interactions, lead to the formation of a stable complex in the following stages (i) Acid-base interactions, (ii) Formation of metal-aqua complexes; (iii) Interaction between acid-base and metal-aqua complexesA series of experiments have been carried out with several divalent and trivalent metals and it was found that the divalent metals enter the composition more easily than trivalent metals However, nutrient material show that only Al” enters the composition readily forming Na2H|AI(P2()7)j even at lower PT conditions (P < 100 bars, T ~250l’C), while others insist upon higher temperature of synthesis |5|3. MorphologyA number of factors such as the degree of supersaturation, type of the solvent, pH of the mineralizer, etc alfecl the habit of crystal Habit modifications occur with significant changes in the growth temperature and also with the presence of impurities in the growth media [6] The pyrophosphates show a wide range of morphological variations The characteristic habits of72A( I j-24 K Bvmppa and B S a n jem  Ravi Rajsome selected pyrophosphates are shown in Figures l(a-g) The habits exhibited by these pyrophosphates are given in Table 2 The crystal faces of most of the superionic pyrophosphates a,e more or less smooth and vitreous in lustre, and transparent The morphology of these pyrophosphates varies from one another depending upon the cations present.Table 2 Morphology of pyrophosphatesCompound System Crystal form(s)Na,ll)AI(l’J0 7)! Monoclinic Third order pinacoid side pinacoidHNaCoPjO, Triclinic Third order pinacoid Second order pinacoid Fourth order pinacoidHNaNiP20 7 Triclinic Basal pinacoid positive and negative third order pinacoidHNaZnPzO, Triclinic Basal pinacoid positive and negativea-HNaMnPjO, Triclinic Second order pinacoidIINaCdPjO, Triclinic Basal pinacoid ’ positive and negativeHNaPbP,0? Triclinic Basal pinacoidNaFeP?0 7 Monoclinic Side pinacoidpositive and negative pinacoidsNa2CaMn2P2()7 Triclinic Third order pinacoidCrystal growth, morphology and properties etcPlate 1(a)K Ihnippa and B Sunjeeva Ravi RajPlate 1(b)(0( X 2 0 )"f mophnsphurc c,.vs,als «■’> HNaZnPnOCrystal growth, morphology and properties etc 5Similarly, the morphology varies with respect to the degree of supersaturation, the concentration of H,0, ? p s and Na,0 in the systemIt is interesting to observe that the morphology of superionic pyrophosphates vary with the variation in the cation. The cations used in the present work are Al, Mn, Co, Ni, Zn, Cd and Pb The Table 3 shows the cation properties. As evident from Table 3, the Al is the smallest ion and it show the excellent morphology (Figure la). Crystals are well developed and highly transparent This is followed by Mn, which gives good crystals of excellent crystal habit. However, due to the susceptibility of Mn for the changes in the valency with sudden changes in the experimental growth parameters, there is a tendency for the formation of polymorphic modifications of Mn bearing superionic pyrophosphates. But both the polymorphic modifications of Mn superionic pyrophosphates show excellent morphology with well developed habit, smooth and vitreous surfaces (Figure lb)Table 3. Cations In superionic pyrophosphatesKlcmcnl Al. No. Al. Wl. Al. radii* (*)Fintropy at 298°K (c.u)Al 13 65.38 182 6 769Mn 25 54.93 1 79 7 59Co 27 58.93 167 68Ni 28 58 70 162 7 137Zn 30 65.38 1 53 9 95Cd 48 11241 171 123Pb 82 207 20 181 15 49* ret Table of periodic properties of the elements, Sargent-Welch Scientific companyThe cobalt bearing superionic pyrophosphate shows probably the best morphology (Figure lc) The crystals are developed very well with vitreous, smooth and transparent surfaces. The cobalt bearing superionic pyrophosphates are bigger than the other pyrophosphates It is observed that in spite of the same crystal structure exhibited by all these pyrophosphates, they slowly lose their morphology The crystal habit in Ni is better than in Zn, because the crystals are well developed, but the crystals are mostly slender or rod shaped, transparent with smooth and vitreous surfaces (Figure Id)In case of/n, there is a fall in the morphological development (Figure le) like crystal habit, lustre, and transparency When we come to the Cd bearing pyrophosphate the morphological variations are still less with the crystals loosing their size, well developed habit, smooth surfaces and vitreous lustre and a low degree of transparency (Figure If). When the crystal surfaces were observed under higher magnification, they show more or less rough surfaces with defect structuresIn case of Pb bearing surpeionic pyrophosphates, it is still worse The crystals do not have well defined crvstal habit, but instead, they look more or less rounded and clustered6 K  B y r a p p a  a n d  B  S a n jc e v a  R a v i  R a jS2•Sir:•8<of3a .35= f«=> aES  1NaZnHP.OCrystal growth, morphology and properties etcPlate 11(a)( X  100)(a)Figure 2. Shows (he growth layers on (010) face of pyrophosphate crystals : (a) HNaCoNiPiOjand (b) a-HNaMnP207;K Ryrappa and R Sanjeeva Ravi Raj(C)(d )Figure 2. Shows rhe growth Iayeis on (010) face of pyrophosphate crystals ■ (c) HNaZnFSCband (d) HNaNiP 1O7Crystal growth, morphology and properties etcPlate 111(a)(b)Figure 3, Shows the macro steps in pyrophosphate crystals : (a) HNaCoP2 C>7and (b) a-HNaNhrf^O/.Cry stal growth, morphology and properties etcPlateFigure 3. Shows the macro steps in pyrophosphate crystals (c) HNaZnP2<I>7Crystal growth, morphology and properties etc 7(Figure Ig). The crystals appear translucent with dull lustre and without smooth surfaces. There is a general tendency for the crystals to become polycrystalline from Mn end to the Pb end.It is believed that all these superionic pyrophosphates belong to the same structure tyep,i.c triclinic, P, space group As the ionic size of the cations inserted into the structure increases, there develops a general structural distortion which in turn, affects the crystal morphology. The Table 4 shows the variation in bond lengths of these superionic pyrophosphates. As evident from the Table 4, the difference in maximum and minimum bond lengths of Na-0 polyhedra increases gradually towards the Zn end member. Thus towards the Pb end member, the crystals become poorly developed The poor morphology of Cd and Pb bearing superionic pyrophosphates is due to the changes in the bond lengths and bond angles leading to the slightly higher degree of structural disorder as indicated by the preliminary X-ray single crystal diffraction studies. Also it is evident fromjable 3 that the values of entropy for Zn, Cd and Pb gradually increase and these values are quite high compared to those of Mn, Al, Co or Ni Entropy is directly related to the structural disorder Thus, the thermodynamic properties of the cations also directly influence on the morphology of these new superionic pyrophosphates.The superionic pyrophosphates show very interesting surface morphology and it varies accordingly with the growth temperature, degree of supersaturation and the cation in the nutrient. These variations also depend on the magnitude and anisotropy of the growth rates along different directionThe most commonly observed surface growth features are growth layers, grwoth steps and block structures The surface morphology of these superionic phosphates is given in Table 5 Since these crystals belong to the lower symmetry, the effect of growth temperature, degree of supersaturation and the impurity concentration is very well depicted in their surface morphologyTable 5 Surface morphology of HNaCoP,0, and HNaNiP20 7 crystalsComposition Growth temp (*C ) Common faces G row ih rate Growth features FaceH N a C o P jO j 2 5 0 ( 1 1 0 )  ( 0 1 0 )  (1 1 0 ) V ( 1 0 l )  >  V ( 0 1 0 ) G r o w th  la y e rs  b lo c k  s tru c tu res( 0 1 0 )H N a N iP jO , 2 5 0 ( 1 1 0 )  ( 0 1 0 )  ( O i l ) V ( 1 1 0 ) >  V ( 0 1 0 ) M a c r o  steps  b lo c k  s tru c tu res( 1 1 0 )I I N a Z n l ’ , 0 ; 2 5 0 ( 1 1 0 ) ( 1 0 1 )  ( O i l ) V ( I I 0 ) >  V ( 1 0 1 ) M a c r o  steps  b lo c k  s tru c tu res  g ro w th  la y e rs( 1 0 1 )„„ . . : B'uwm layers on tne race (010) of the pyrophosphaterys a s. Similarly Figures 3(a-c) respresent the macro steps observed in the pyrophosphate crystals As the supersaturation increased, the spirals must have become rounded. The Figure ' T  °n yL°"e h,lf of the spiral s/layers With an increase in the supersaturation and thermal ci lations, the number of macro spirals increases and a large number of thick steps appear on ■ u ace as shown in Figure 3a The crystals obtained from experiments with surplus Na20g KByrappa and BSanjeeva Ravi Rajr n l l -ii.v may be because of the increase in the viscosityfe r.« « i m M -  -and also the high solubility of pyrophosphates in H,PU4.„,.r ^ s s  t t s t t x x z z s z«  “  I * * * * - . ........ ...  « . . .r .K . «y« .l « p k * W . TJ-A ’ Co and Ni members show orderly arranged spirals and even a single large spiral occasionally steps and block structures Whereas the Cd and Pb end members manly ^wW ock wdstep structures and highly discountinous surface structures. This is again connected with the highly distorted polyhedra and octahedra owing to the larger ionic radii of the transitional metals and also highly distorted polyhedra of Na-O coordination towards Cd and Pb end.4. Charactcrizition jIThe supcnonic pyrophosphates crystals obtained were characterised using different techihques like XKI). I'l’MA and impedance spectroscopy The single crystal X-ray data for the supetionic pyrophosphates is given in I able 6 liPMA analysis is given in Table 7.Table 6 X-ray data of superionic pyrophosphatesCompound System Space Cell parameters Agroupa b c p<°>VAJZN V IIW M , Triclmic PI 8311 (4) 7 363 (4) 4.902 (3) 81 77(2) 2£8 2(4) 1tt - HNaMnP;0 7 Monoclinic Cv 9 935 (4) 8 455(3) 13 106(4) 110 75 1029(1) 8P-HNaMnl’,07 Tnclmc PI 6657(1) 7 372(1) 6 517 (1) 9222 1029 8HNaCoP,07 Triclinc PI 6 5190(6) 6 595 (1) 6 485 (1) 92 07 255 97(7) 21 INaNiP?()7 Incline PI 6 502 (3) 6 418(1) 6 442(2) 91 83 (l) 249 33 (7) 2IINaZnP;0 7 1 riclmc PI 6 509 (3) 7 250(3) 6 486(2) 92 09 260 37 (7) 2IINaCdP70 7 Triclinc PI 6612 6 674 6 597 92 75 290 78 2NafcP,()7 Monoclinic II 83 12 527 6 44 114 18 870 63 (2) .The CIS measurements were carried out using Solatron Impedance Analyser system (Model 1260) from I I Iz to 32 Ml Iz I he pellets were made by pressing the superionic polycrystalline powder at 5 ton/cm 3 pressure The impedance data was analysed using EQUIVALENT C1R- CU11 ( KQUIVCRT PAS) PROGRAM [7] The complex impedance data has been analysed to extracl the bulk resistance (Rb) and hence a c conductivity (a^Crystal growth, morphology and properties etcPlate IV(b)Figure 4. Shows etch pits and block structures in pyrophosphate crystals (a) HNaCoP^O; and (b) HNaNiP2C>7The Figure 5 shows the Arrhenius plot ( In abT vs 1000/T) The Arrhenius plot show single phase with an activation energy 1 1 eV for lower temperature region up to 423 K Above 423 K - 523 K, the Arrhenius plot is not linear Non-linear Arrhenius plot may be explained in terms of inlerfa- cial flicker noise due to polarization at the sample-electrode interface.Table 7. EPMA analysis of supenonic pyrophosphatesCrystal growth, morphology and properties etcOxide IINh(W 2( )7 Wi%IIN;iNi1M)tWl%IlNaZnP^Wl'lHNaMnPjO,wiaNa,(> 09.92 11.07 11,42 11.17CoO 30.07 00.10 (K).IO (M).OO/.it), (HUM) 00.00 (M).OO 00.00■M>, 59.45 58.18 57.94 57.40NiO 00.04 31 II 00.00 00.00/n() 00.00 (M).OO 31.03 (M).OOMn() 00.12 (Ml.25 00.21 32.31Cat) 00.04 00.00 (M) 00 (M).OOIvO 00.04 00 22 00.04 (MUMfi(). 00.07 00.02 00.01 00.01loUl |(M) IS lOl'SO 101 25 99.9910VT (k)Acknowledgments FiRurr 5 Anhcmus P'01 Por pyrophosphatesI lie an lhois wish u> thank Pi o f  A 11 K u lkam i, D epailm cnl o f  Applied h lcc lion ics , Ciulbargalin ive is ilv , ( iu lha tga , lo t the help in impedance speclioscopy10 K Byrappa and B Sanjeeva Ravi RajReferences111 S Gali,K Dyrappa and G S Gopalkrishna c^to Cryst. ,C4& 1667 (1989)|2] K Etyrappa,G S Gopalkrishna and SGnhJndiatLj.Phy.&A 321 (1989)|3] S Gall and K ByrappM^ Cry si, C46 (1990)[41 K Burger Solvation, lame and (vmplex Formation Reaction in Non-Aqueous Solvents (Budapest Academial Kiaddo) 42 (1983)[5J K Byrappa Indian J.Phys 66A 233 (1992)[6] R Kern in Growth of Crystals vol 8 ed. N.N. Sheftal ( New York: Consultants Bureau(l%9)|7| B A Boukamp Equivalent Circuit Users Manual ( University of Twente, The Netherlands) (May 1989)

Crystal Growth, Morphology and Properties of NaHMP2O7 (M = Ni, Co, Mn, Zn, Cd, Pb)

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Crystal Growth, Morphology and Properties of NaHMP2O7 (M = Ni, Co, Mn, Zn, Cd, Pb)

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