Gupta, S P Sen

Gupta, S Sen

Kar, T

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U P  A— an international journalGrowth defects in pure and mixed crystals of KDP- ADP by X-ray Lang Topography jS Sen Gupta, T  Kar and S P Sen Gupta Departmenr of Matenals Science, Indian Association^ for the ruUivation of Science, Jadavpur, Calcutta-700 032, India-Received JO September 1998, accepted 27 November 199$Abstract : A full senes of compositions of KDP-ADP mixed crystals were grown by slow evaporation method. Crystals having habitual faces were grown from the end composition. X-ray topographs of pure KDP, pure ADP and mixed KDP-ADP were taken by Lang transmission method. A(wt from dislocations, growth imperfections such as growth bands, lattice deformation at the boundary between two growth sectors (pnsmatic and pyramidal) and inclusions present in the crystal were observed and analysed.Keywords : Soluuon growth, mixed KDP-ADP, X-ray Lang Topography PACS Nos. : 81.10 Dn, 77.84.Fa, 61.72.Ef1. In tro d u c tio nriie siudy o f m ixed crystals o f Potassium  Dihydrogen O rthophosphate and A m m onium  D ihydrogcn O rthophosphate (KDP : ADP) has atuactcd  considerable attention during recent years due to the ir w ide spread app lications in quantum  elec tro n ics  and optoelectronics. A  lot o f studies have been reported by several workers on KDP and ADP crystals [1,2]. W e have also done some work on pure KDP and ADP in the light o f their physical property like m icrobardness [3] and dielectric constant measurem ents [4]. Apart from this som e defect characterization studies by chemical etch pit m ethod have also been reported by us [5,6]. But only very few reports are available during the la.st several years on mixed K D P : A D P system  [4,7-12]. Recently the study of variation o f m icrobardness num ber with load for a  wide range of com position for solution grown m ixed K D P-A D P crystal has been done by us [13]. Beside this, the variations o f  lattice param eters with com position using X -ray diffraction technique were studied by some w orkers [4,14,15]. Chemical etching technique has also been a i^ lied  with greater details to reveal dislocations in mixed system  [16,17].© 1999 lACS338 S Sen Gupta, T Kar and S P Sen GuptaTo asses the quality o f the crystals in terms of grown-in-defects on planar habit faces o f pure KDP and pure ADP crystals, extensive X-ray topographic studies (XRT) [18,19] have been made in past years [20-25]. Very little work has been done on XRT of mixed KDP-ADP system with variations o f compositions [26].In the present work, we have done topography work on as-grown single crystals of pure and m ixed KDP-ADP system by Lang transmission m ethod [27-29]. Similar to KDP typo crystals [25], we have also observed clear growth sector boundaries and g r o ^  bands along with dislocations originating from inclusions and the crystal seed.2. C ry sta l g row thSaturated solutions o f various com positions ranging from 5% ADP to 95% A D P were mixed with KDP solutions and allowed for slow evaporation. Crystals having habitual faces have been harvested from the end compositions. Needles typo crystals were obtained at the intermediate range.Thin ‘c ’ cut plates o f the samples with dimensions about 8 mm x  7 mm x 2 mm were pnepared from good quality crystals grown by slow evaporation. For each composition three different pmtjecticm topographs were taken with 222 ,020  and 022 reflections on Ilford GS nuclear emulsion plates, using a  Rigaku X-ray topographic cam era and Radon House X -ray generator with M oK a (A = 0.7107 A). Recorded plates were develojod with Kodak D 19b developjCT, and enlarged in Carl-Zeiss optical microscopo.3. R esults an d  discussionFigures 1 (a, b, c) show X-ray tojographs of (001) plate o f a KDP crystal cut very near to the seed region with a string saw. The cut surfaces were polished by gently moving the plate on a  soft m oist cloth wetted with a m ixture o f 50% ethyl alcohol and 50% double di.stilled water. In Figure 1 (a, b) the position o f the seed can be detected through a strong constrast. All the growth sectors and boundaries between the prism atic and the pyramidal regions are very clear with good contrast. The starting ptoints of dislocations propagating in the four grow th sectors are also seen. These topwgraphs have been com pared with a schem atized representation o f all kinds of growth bands and sector boundaries as shown in Figure 2 [25].It is found that in Figures la  and lb  (200 and 020 reflection), num erous growth bands w ith different contrasts are clearly visible in the two opposite pyram idal sectors. W ell-resolved dislocation lines originating from seed have also been observed on pyramidal faces in (200) and (020) reflections. Growth sector boundaries are revealed by black or white contrast in the case o f symmetric reflections (200 and 020), while with asym m etric reflection (022) boundaries becom e faint and contrast is not visible (Figure Ic), due to oblique angular pvojections.S Sen Gupta, T Kar and S P Sen GuptaPlate /(a)ngar«  1. X-ray topographs of (001) section of pure KDP crystal for (a) (200) and (h) (020)reflection.Growth defects in pure and mixed crystals ofKDP-ADP etcPlate I (C o n rtL )( c )Figure 1. X-ray topographs of (001) section of pure KDP crystal for (c) (022) reflection.Growth defects in pure and mixed crystals ofKDP-ADP etc 339Usually in solution-grown KDP and ADP crystals, these kinds o f growth bands and sector boundaries have been observed in both prismatic and pyramidal sectors [21,23,25]Figure 2. Schematic representation of the growUi sectors and the boundaries between them for an idealized situation of projection on the (001) plane in X-ray transmission topograpiLSand correlated bands with the impurity content in these growth sectors [21,22]. Due to (he variations o f supersaturation, prismatic growth sector consists o f successive layers largely different in their impurity content and consequently w ell-depicted contrasting bands arc visible in the topographs. Both growth bands and sector boundaries originate from lattice deform ations due to a difference in lattice parameters in adjacent regions caused by a local variation in impurity content, which leads to local strain field in these crystal areas. It has been concluded from X-ray diffraction topography, that the strain field around the.se sector boundaries can arise in two ways : (i) by a slight angular misorientatiffli between two neighbouring sectors or (ii) by a distortion in lattice param eter due to a segregation o f impurities leading to a  difference in unit cell parameters between adjacent seettws [21].Figure 3(a) shows the topographs o f (001) slice o f pure ADP crystal cut far fiom the seed. All the topographs show the perfection o f crystal as few liquid inclusions are visible. Local variation o f supersaturation and sudden fluctuation in growth conditions also lead to liquid inclusions in the case o f crystals grown from solution. It was observed that a strain has developed around the central nucleation point and also around few inclusions which are trapped in the crystal during growth. Bunches of dislocations also emerge from the seed73A(3>-10340 S Sen Gupta, T Kar and S P Sen Guptaand inclusions [27]. By comparing the Figure 3(a) with the Figure 3(b), (taken from the plane (022)), it is clearly observed that the dislocations em erging from  the inclusion disappears in topogrt^A (Figure 3b). The invisibility proves the fulfilment o f the criteria of g.b = 0  (m inim um  contrast). In Figure 3a, Burger vector (b) is neither parallel nor perpendicular to the dislocation line direction /, revealing that dislocations are o f m ixed type. Figure 4 (a, b) show the topographs of ADP-KDP mixed crystals (KDP-95%, ADP- 5%) for (200) and (020) reflection. In these topographs the position o f the seed is found to be eccentric which may be due to the difference in growth rates between two opposite growth sectors. This difference will also lead to misorientation between growth sectors. These growth bands in all the topographs are aligned norm al to the growth directions. In this case the impurities pre.sent in the individual components (ADP content) will play an im portant ro le in the creation o f growth bands in the pyram idal grow th sectors, 'fhe  visibility o f growth bands in the topographs o f (200) and (020) reflections show that the lattice displacem ent due to these growth bands are parallel to [100] and [010] respectively.4. C onclusionsWe have characterised the general features o f grown-in defects in crystals grown on planar habit faces with the help o f  Lang X -ray topography techniques. The common defects such as dislocations, growth bands, growth sector boundaries, liquid inclusions etc have been clearly observed on KDP, ADP and al.so on m ixed KDP-ADP crystals. The types o f  dislocations on ADP crystals were found to be o f mixed type although detailed analysis from g.b criterion from a num ber o f topographs is necessary to arrive at the characterizations o f the dislocations revealed in as-grown crystals. It is very clear that the grow th im perfections like growth bands, growth sector boundaries as revealed by XRT present in the A D P-K D P m ixed crystals are very sim ilar to those in the pure systems.A cknow ledgm entsOne o f the authors (SSG) is thankful to the Council o f Scientific & Industrial Research, India for awarding a Research Associateship.References111 R D Deslattes, J L Torgeson, B Paretzkin and A T Horton 7. Appl. Phys, 37 541 (1966) 121 K V Ramaiah and K B R Varma Bull. Mater. Sa. 5 147 (1983)(3J S Sen Gupta and S P Sen Gupta Bull. Mater. Sa. 15 333 (1992)(4J S Sen Gupta, T Kar and S P Sen Gupta Mater. Chem. Phys. (accepted) (1999)[5] S Sen Gupta, T Kar and S P Sen Gupta 7. Mater. Set. 27 5935 (1992)f6J S Sen Gupta, T Kar and S P Sen Gupta Jpn. J. Appl Phys. 32 1160 (1993)(7] B Matthias and W Mertz Helv. Phys. Acta. 19 222 (1946)S Sen Gupta, T Kar and S P Sen GuptaPlate II(a )(b)F ig u re  3. X -ray  topographs o f (001) section of pure AJJP crystal for (a) (020) and (b) (022) reflection.Growth defects in pure and mixed crystals ofKDP-ADP etcPlate inC 2 0 6 3(a)(b)Figare 4. X-ray topographs of (001) se«ion of mixed KDP-95%-ADP-5% crystal for (a) (200) and (b) (020) reflection.Growth defects in pure and mixed crystals of KDP-ADP etc 341[8] K B R Varma and K V Ramaiah Bull. Mater. Sci. 3 307 (1981)[9] M Shanmugham, F D Gnanam and P Ramasamy J. Mater. Sci. Lett, S 174 (1986)[10] S Anbukumar, S Vasudevan and P Ramasamy J. Mater. Sci. l^tt. S 224 (1986)[11] Y Kjm» S I Kwun, S Park, B Oh and D Lee Phys. Rev. B28 3922 (1983)[12] Y Ono, T Hikila and T Ikeda J. Phys. Sac. Jpn. 56 577 (1987)[13] vS Sen GupU and S P Sen Gupta J. Mater. Sci. Lett. 15 525 (1996)[14] I Nitta, R Kriyama and M Haisa Sci. Papers (Osaka Untv) 30 (1951)[15] vS K Mohanlal and R Baskaran Cryst. Res. TechnoL 22 21 (1987)[16] O Ravi, K Srinivasan, S Anbukumar and P Rama.samy 7. Cryst. Griinvth 137 598 (1994)[17] S Sen Gupta and S P Sen Gupta 7. Mater. Set. Ijett. 35 6180 (1996)118] A Auihier 7. Cryst. Growth 13/14 34 (1972)119] H Klapper and H Kupers Acta. Cryst. A29 495 (1973)[20] A R Lang 7. AppL Phys. 29 597 (1958)[21] C Belouet, E Duma and J F Petroff 7. Cryst. Growth 23 243 (1974)[22] C Beloucl, M Monnier and J C Verplanke 7. Cryst. Growth 29 109 (1975)[23] <' Belouet and W T Stacy 7. Cryst. Growth 44 315 (1978)[24] C Belouet Prog Cryst. Growth Charact. 3 121 (1981)[25] B Dam and WJP Van Enckevort 7. Cryst. GrowthSl 607 (1981)[26] K Snnivasan, P Ramasamy, T Kar and S P Sen Gupta Mater. Chem. Phys. 49 191 (1997)[27] H L Bhat Prog. Cryst. Growth Charact. 11 57 (1985)[28] A R Lang Modem Diffractron and Imaging Technique eds. S Amelinekx et.al (Amsterdam : North Holland) (1970)[29] B K Tanner X^ray Diffraction Topography (Oxford : Pergamon) (1976)

Growth Defects in Pure and Mixed Crystals of KDP-ADP by X-ray Lang Topography

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Growth Defects in Pure and Mixed Crystals of KDP-ADP by X-ray Lang Topography

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