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Synthesis, growth, structure and characterization of nickel(II)-doped hexaaquacobalt(II) dipotassium tetrahydrogen tetra-o-phthalate tetrahydrate crystals
Solid State Sciences 14 (2012) 1355e1360
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Synthesis, growth, structure and characterization of nickel(II)-doped hexaaquacobalt(II) dipotassium tetrahydrogen tetra-o-phthalate tetrahydrate crystals K. Muthu a, G. Bhagavannarayana b, S.P. Meenakashisundaram a, * a b
Department of Chemistry, Annamalai University, Annamalainagar, Chidambaram 608 002, India National Physical Laboratory (CSIR), New Delhi 110 012, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 10 February 2012 Accepted 10 July 2012 Available online 20 July 2012
Single crystals of K2[Co(1x)Nix(H2O)6] (C8H5O4)4$4H2O (x ¼ 0.25) (PCNHP), a semiorganic black colored transparent crystal of size w20 13 4 mm3, are grown from an aqueous solution of potassium hydrogen phthalate enriched with cobalt chloride and nickel chloride by slow evaporation solution growth technique at room temperature. Structural analysis by single crystal X-ray diffraction reveals that the crystal belongs to monoclinic system with space group P21/c and the cell parameters are a ¼ 10.41(3) Å, b ¼ 6.84(2) Å, c ¼ 29.46(9) Å, Z ¼ 4. Incorporation of both Co(II) and Ni(II) into the potassium hydrogen phthalate (KHP) crystal lattice is well confirmed by EDS and chemical tests. Powder XRD profiles indicate the crystallinity and FT-IR studies reveal the vibrational patterns. The UVevis optical absorption spectrum of PCNHP shows the lower optical cut-off at w300 nm and the crystal was transparent in the entire visible region. The crystalline perfection of the grown crystal analysed by high-resolution X-ray diffraction (HRXRD) analysis reveals that the diffraction curve (DC) contains multi-peaks with low angular spread indicating the possibility of low angle structural grain boundaries. Scanning electron microscope (SEM) studies indicate the structure defect centers. The dielectric, thermal and mechanical behaviors of the specimen were also investigated. Crown Copyright Ó 2012 Published by Elsevier Masson SAS. All rights reserved.
Keywords: Intermetallic compounds Crystal growth High resolution X-ray diffraction Differential scanning calorimetry (DSC) Dielectric properties Mechanical properties
1. Introduction Crystals of phthalic acid derivatives are potential candidates for nonlinear optic and electro-optic processes. Acid phthalate crystals are crystallized as noncentrosymmetric or centrosymmetric structures depending on the nature of the cations, since in 3D crystallographic frame work the bonding orientation of growth unit is dramatically determined by these cations, on the basis of the chemical bonding theory of single crystal growth [1,2]. KHP possesses piezoelectric, pyroelectric, elastic and nonlinear optical properties [3e6]. It crystallizes in orthorhombic structure with space group Pca21 [7]. The influence of magnetic field on the microhardness of various metal phthalate crystals was reported by Koldaeva et al. [8]. The optical, dielectric, thermal properties [9] and structure [10] of lithium hydrogen phthalate have been investigated. It was observed that the second harmonic generation (SHG)
* Corresponding author. E-mail address: [email protected] (S.P. Meenakashisundaram).
efficiency of sodium hydrogen phthalate is double that of KHP crystals [11]. Single crystals of Sr(C8H5O4)2$2H2O were grown from an aqueous solution of SrCO3 and an excess of phthalic acid [12]. Structure of cesium(I) hydrogen phthalate reveals that Csþ cation is surrounded by eight O atoms [13] while Mg2þ cation is octahedrally coordinated in hexaaquamagnesium hydrogen phthalate [14]. Manganese dihydrogen diphthalate dihydrate crystallizes in the monoclinic space group P21/c [15]. The structures of [Co(H2O)6](C8H5O4)2 [16,17] and NiH2(C8O4H4)2$6H2O [18] consist of octahedrally coordinated cations [17]. Much structural work was performed on phthalate complexes of metal ions Tlþ$C8H5O 4 [19] and Rbþ$C8H5O 4 [20]. Influence of alkaline cation on the structure of polymeric o-phthalatocuprate(II) has been studied [21]. Molecular structures of magnesium di-o-phthalatocuprate(II) dihydrate and strontium di-o-phthalatocuprate(II) trihydrate [22] crystals consist of o-phthalatocuprate(II) complexes, joined in linear polymeric chains by bridging o-phthalate anions, of alkalineearth cations and of water molecules. Polymeric dihydroxydiphthalato tricobalt(II) crystallizes in orthorhombic space group Pccn [23]. Molecular structures of K2[Ni(H2O)6](C8H5O4)4$4H2O [24] and K2[Co(H2O)6](C8H5O4)4$4H2O have been reported [25].
1293-2558/$ e see front matter Crown Copyright Ó 2012 Published by Elsevier Masson SAS. All rights reserved. http://dx.doi.org/10.1016/j.solidstatesciences.2012.07.016
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K. Muthu et al. / Solid State Sciences 14 (2012) 1355e1360
Recently, we have investigated the influence of rare earth, alkaline earth and transition metals doping on the properties and crystalline perfection of KHP crystals [26,27]. It is interesting to observe that the alkaline earth metal Mg occupies predominantly substitutional positions while the transition metal Hg mainly occupies the interstitial sites. Also, accommodating capability of KHP crystals with dopants like Os(VIII) [28], Zn(II) [29] and sodium [30] revealing some interesting features has been analysed. In the present investigation, we report the growth, structure and crystalline perfection of a new mixed phthalate complex crystal. Influence of the impurities Co(II) and Ni(II) defecting the structure of KHP and the systematic analysis of the phthalate K2[Co(1x)Nix(H2O)6](C8H5O4)4$4H2O (x ¼ 0.25) by various characterization techniques have been detailed.
2. Experimental 2.1. Synthesis and crystal growth PCNHP was synthesized by dissolving the stoichiometric amounts (0.5:0.5:4.0) of AR grade cobalt(II) chloride haxahydrate (Qualigens), nickel(II) chloride hexahydrate (Qualigens) and potassium acid phthalate (Qualigens) in de-ionized water. Purified by recrystallization process using de-ionized water as solvent. Crystals were grown by slow evaporation solution growth technique. The crystallization took place within 15e16 days and the crystals were harvested when they attained an optimal size and shape. Photographs of as-grown PCNHP crystals are shown in Fig. 1.
Fig. 1. Photographs of as-grown PCNHP crystals.
2.2. Characterization The Fourier transform infrared (FT-IR) spectrum was recorded using AVATAR 330 FT-IR by the KBr pellet technique. A Bruker AXS (Kappa Apex II) X-ray diffractometer was used for single crystal Xray diffraction (XRD) studies. The powder X-ray diffraction was performed by using a Philips Xpert Pro Triple-axis X-ray diffractometer at room temperature using a wavelength of 1.540 Å and a step size of 0.008 . The samples were examined with CuKa radiation in a 2q range of 10e70 . The XRD data were analysed by the Rietveld method with RIETANe2000. To evaluate the crystalline perfection of the specimen crystals, HRXRD analysis was carried out. A multicrystal X-ray diffractometer developed at National Physical Laboratory (NPL), New Delhi [31] was used to record high-resolution diffraction curves (DCs). In this system, a fine focus (0.4 8 mm2; 2 kW Mo) X-ray source energized by a well-stabilized Philips X-ray generator (PW 1743) was employed. The well-collimated and monochromated MoKa1 beam obtained from the three monochromator Si crystals set in dispersive (þ,,) configuration has been used as the exploring X-ray beam. The DCs were recorded by changing the glancing angle (angle between the incident X-ray beam and the surface of the specimen) around the Bragg diffraction peak position qB (taken zero as reference point) starting from a suitable arbitrary glancing angle (q). Before recording the diffraction curve, to remove the non-crystallized solute atoms remained on the surface of the crystal and also to ensure the surface planarity, the specimens were first lapped and chemically etched in a nonpreferential etchant of water and acetone mixture in 1:2 volume ratio. The morphologies of the samples and the presence of dopants in the specimens were observed by using a JEOL JSM 5610 LV scanning electron microscope with a resolution of 3.0 nm and accelerating voltage 20 kV. The UVevisible transmittance spectrum was recorded using Hitachi UVevis spectrophotometer in the spectral range 200e800 nm. DSC analysis was carried out using SDT Q600 (TA instrument) thermal analyzer. Vickers microhardness was evaluated for the well polished grown crystal using Reichert 4000E Ultramicrohardness tester. Dielectric measurements were carried out by the parallel palate capacitor method as a function of temperature for various frequencies using a precision LCR meter (AGILENT 4284 A model).
Fig. 2. Powder XRD pattern of PCNHP crystal.
K. Muthu et al. / Solid State Sciences 14 (2012) 1355e1360
3. Results and discussion
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Table 1 Crystal data of PCNHP single crystal.
3.1. X-ray diffraction analysis The powder XRD pattern of PCNHP crystal shows that the sample is of single phase without detectable impurity. Narrow peaks indicate the good crystallinity of the material. At room temperature all the observed reflections were indexed. The indexed powder XRD pattern of the as-grown PCNHP crystal is shown Fig. 2. The structure of PCNHP single crystal is analysed by single crystal XRD and the ORTEP diagram is given (Fig. 3). The chemical formula C16H20Co0.38KNi0.12O13 well supports the presence of Co(II) and Ni(II) in the crystalline matrix. It crystallizes in the monoclinic system with centrosymmetric space group P21/c and crystal data are given in the Table 1. The crystal structure consists of octahedral hexaaquacobalt cations, hexaaquanickel cations, Kþ ions, hydrogen o-phthalate anions and water molecules. The phthalate ions are connected in chains by short intermolecular hydrogen bonds. The Kþ ions are surrounded by oxygen atom and the Kþe O distance range is slightly higher in the case of mixed crystal (2.73(3)e3.28 (8) Å) in comparison with Ni(II) phthalate (2.67(9)e3.11(4)Å) and Co(II) phthalate (2.63(9)e3.24(4)Å) complexes. The MdOH2 distance range in the case of mixed crystal (2.04(2)e2.09(3) Å) is in close proximity with the reported values for Ni(II) phthalate (2.035(3)e2.072(3) Å) and Co(II) phthalate (2.05(2)e2.102(5) Å) complexes. The strongest hydrogen bond is observed between O1eH1dO7 (2.41 Å) and weak one for O10eH10 (B)dO2 (2.926 Å). 3.2. HRXRD analysis Fig. 4 shows the high-resolution rocking curve (RC) recorded for a typical PCNHP single crystal specimen using (200) diffracting planes in symmetrical Bragg geometry by employing the multicrystal X-ray diffractometer with MoKa1 radiation. As seen in the figure, the curve is not having a single diffraction peak. The solid
Chemical formula Chemical formula weight Unit cell parameters
Crystal size Volume Color Crystal system Space group Z Calculated density Radiation (l, Ǻ) Temperature
C16H20Co0.38 KNi0.12O13 488.86 g/mol a ¼ 10.4131(3)Ǻ b ¼ 6.8487(2)Ǻ c ¼ 29.4607(9)Ǻ b ¼ 98.064(10) 0.25 0.20 0.15 mm3 2080.25(11)Ǻ3 Black Monoclinic P21/c 4 1.561 g/cm3 MoKa (0.71073) 293 (2)K
line, which follows well with the experimental points (filled circles), is the convoluted curve of two peaks using the Lorentzian fit. On deconvolution of the diffraction curve, it is clear that the curve contains two additional peaks, which are 455 and 405 arc sec away from the central peak. These two additional peaks correspond to two internal structural low angle boundaries whose tilt angles are 455 and 405 arc sec from their adjoining regions. The FWHM (full width at half maximum) of the main peak and the boundaries are 204, 300 and 510 arc sec as depicted in the figure. The relatively high values of FWHM indicate that various regions (grains) of the crystal contains mosaic blocks which are misoriented to each other by at least a few tens of arc sec. Though the crystal contains a low angle boundary, the low angular spread of around 1200 arc sec (20 arc min) of the DC indicates that the quality of the crystal is fairly good. The influence of such defects may not influence much on the NLO properties. However, a quantitative analysis of such unavoidable defects is of great importance, particularly in case of phase matching applications as explained in our recent article [32].
Fig. 3. ORTEP diagram of PCNHP crystal.
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K. Muthu et al. / Solid State Sciences 14 (2012) 1355e1360 Table 2 FT-IR frequencies of some acid phthalate crystals. S.No
KHPa
LiHPb
NaHPc
PCNHP
Frequencies (cm1)
1 2 3 4 5 6
1090 1144 1445 1565 1675 3470
1072 1172 1401 1552 1685 3391
e e e e 1719 e
1079 1149 e 1551 1695 3375
nasOeHeO ns(OeHeO) nasOeC]O nsOeC]O ns(C]O) ns(OeH)
a b c
Ref. [6]. Ref. [9]. Ref. [11].
color precipitate confirms the presence of Ni(II). To another portion of the test solution dry ammonium thiocyanate crystals and amyl alcohol are added. The formation of the blue alcohol layer confirms the presence of cobalt(II). Fig. 4. HRXRD curve recorded for PCNHP crystal.
3.5. Optical transmission spectral analysis 3.3. FT-IR analysis The FT-IR spectrum (Fig. 5) of PCNHP crystal shows an absorption band in the region 500e900 cm1 due to CeH out of plane deformations of aromatic ring. The C]O stretching frequencies appeared at 1695 and 1640 cm1. The hydroxyl (eOH) stretching frequency appeared at 3375 cm1. The symmetric and asymmetric stretching frequencies of OeHeO appeared at 1149 and 1079 cm1. The characteristic vibrational patterns of some metal acid phthalates along with PCNHP crystal are given in Table 2.
The UVevis spectrum (Fig. 8) reveals that the cut-off wavelength is w300 nm. Absorption is minimum in the 300e800 nm region. Table 3 clearly reveals that the mixed crystal complex formation does not destroy the optical transmission. Because of high transparency, this specimen is quite useful for optical device applications. 3.6. Differential scanning calorimetry (DSC) The recorded DSC spectrum is shown in Fig. 9. The decomposition was recorded from 0 to 300 C. In the DSC curve, sharp
3.4. SEM and EDS analyses Scanning electron microscopic (SEM) study gives information about the surface nature and its suitability for device fabrication. Also it is used to check the presence of imperfections. The SEM pictures of PCNHP crystals at different magnifications are given in Fig. 6, indicating structure defect centers due to the incorporation of foreign metal ions. The presence of Co(II) and Ni(II) in the specimen was confirmed by EDS and it can be clearly seen in Fig. 7. Analysis of the surface at different sites reveals that the incorporation is non-uniform over the whole crystal surface. The presence of nickel and cobalt in the doped crystals is also established by a spot test. To a drop of the test solution (a portion of crystal dissolved in water) on a spot plate, a few drops of dilute dimethyl glyoxime solution and then a little aqueous ammonia solution are added. Development of rosy red
Fig. 5. FT-IR spectrum of PCNHP crystal.
Fig. 6. SEM photographs of PCNHP crystal.
K. Muthu et al. / Solid State Sciences 14 (2012) 1355e1360
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Fig. 7. Energy dispersive spectrum of PCNHP crystal.
Fig. 9. DSC curve of PCNHP crystal.
where P is the applied load in kg and d is the mean diagonal length of the indentation impression in micrometer. A plot of load (P) versus Vickers hardness number (Hv) exhibits that the hardness of the grown crystal increases as the load increases (Fig. 10). Cracks started developing around the indentation mark beyond a load of 100 g. This may be due to the internal stresses released during the indentation. The Mayer’s index number (n) or work hardening index is calculated and it is equal to 3.5, classifying PCNHP crystal to soft material category. 3.8. Dielectric studies
Fig. 8. UVeVis spectrum of PCNHP crystal.
endothermic peaks at 95 C and 107 C are due to liberation of water molecules. The endothermic peaks at 255 and 277 C could be due to the decomposition of residues.
Fig. 11(aec) is the plot of dielectric constant (3 r), dielectric loss (tan d) and AC conductivity (sac) versus temperature at different frequencies of as-grown PNHP crystals. It is observed that the dielectric constant and dielectric loss decrease with increase in frequency and attain saturation at higher frequencies. The AC electrical conductivity increases with increase in frequencies. This is the normal dielectric behavior of the materials. The large value of dielectric constant at low frequency and low temperature could be due to the presence of space charge polarizations which depend on
3.7. Mechanical studies Transparent crystals free from cracks were selected for microhardness measurements. Before indentations, the crystals were carefully lapped and washed to avoid surface effects. The Vickers hardness indentations were made on the as-grown surface of the PCNHP crystal at room temperature with the load ranging 25e100 g, keeping the time of indentations kept as 5 s for all trials. The Vickers hardness number Hv was calculated from the following equation,
Hv ¼ 1:8544 P=d2 kg=mm2 ;
Table 3 UV e cut e off some acid phthalate crystals. S.No
UV e cut e off (nm)
KHPa LiHPb NaHPc PCNHP
w300 w330 w320 w300
a b c
Ref. [6]. Ref. [9]. Ref. [11].
Fig. 10. The plot of Vickers hardness number (kg/mm2) versus load (g) for PCNHP crystal.
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[M(H2O)6]2þ (M ¼ Co(II)/Ni(II)) located between the anionic layers. The low dielectric constant at high frequency is indicative of a less defective good quality optical crystal. Acknowledgments The authors thank SAIF, IIT Madras, Chennai for providing single crystal XRD facility and Dr. C.K. Mahadevan, Physics Research Centre, S.T. Hindu College, Nagercoil for the support in dielectric studies. One of the authors, K. Muthu is thankful to CSIR, New Delhi, for the award of a Senior Research Fellowship. Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.solidstatesciences. 2012.07.016. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] Fig. 11. Dielectric measurements for PCNHP crystal. (a) Plot of dielectric constant vs temperature (K). (b) Plot of dielectric loss vs temperature (K). (c) Plot of AC electrical conductivity vs temperature (K).
[14] [15] [16]
the purity and perfection of the sample [33]. The increase in conductivity could be attributed to reduction in the space charge polarization at higher frequencies [34]. In the present study, dielectric constant varying proportionally with temperature is essentially due to the temperature variation of the polarizability [35]. The low dielectric loss at high frequency indicates that the asgrown crystal has good optical quality with lesser defects. The low 3 r value dielectric materials have potential applications in microelectronic industries.
[17]
4. Conclusions
[25]
A new phthalate complex crystal K2[Co(1x)Nix(H2O)6](C8H5O4)4$ 4H2O (x ¼ 0.25) has been synthesized and the solution growth from de-ionized water yielded the most perfect crystals in sizes of w20 13 4 mm3. Structural analysis by single crystal XRD analysis confirms the coexistence of Co(II) and Ni(II) in the complex and the presence of the metal in the product is supported by the EDS and chemical tests. DSC and FT-IR support the formation of the hydrated complex. Investigations reveal low cut-off wavelength, good transparency in the visible region, proportional increase of hardness with load and defect centered external morphology. Multi-peaks in HRXRD correspond to internal structural low angle grain boundaries which might be due to strains developed by the octahedral
[26]
[18] [19] [20] [21] [22] [23] [24]
[27] [28]
[29] [30] [31] [32] [33] [34] [35]
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Contents lists available at SciVerse ScienceDirect
Solid State Sciences journal homepage: www.elsevier.com/locate/ssscie
Synthesis, growth, structure and characterization of nickel(II)-doped hexaaquacobalt(II) dipotassium tetrahydrogen tetra-o-phthalate tetrahydrate crystals K. Muthu a, G. Bhagavannarayana b, S.P. Meenakashisundaram a, * a b
Department of Chemistry, Annamalai University, Annamalainagar, Chidambaram 608 002, India National Physical Laboratory (CSIR), New Delhi 110 012, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 10 February 2012 Accepted 10 July 2012 Available online 20 July 2012
Single crystals of K2[Co(1x)Nix(H2O)6] (C8H5O4)4$4H2O (x ¼ 0.25) (PCNHP), a semiorganic black colored transparent crystal of size w20 13 4 mm3, are grown from an aqueous solution of potassium hydrogen phthalate enriched with cobalt chloride and nickel chloride by slow evaporation solution growth technique at room temperature. Structural analysis by single crystal X-ray diffraction reveals that the crystal belongs to monoclinic system with space group P21/c and the cell parameters are a ¼ 10.41(3) Å, b ¼ 6.84(2) Å, c ¼ 29.46(9) Å, Z ¼ 4. Incorporation of both Co(II) and Ni(II) into the potassium hydrogen phthalate (KHP) crystal lattice is well confirmed by EDS and chemical tests. Powder XRD profiles indicate the crystallinity and FT-IR studies reveal the vibrational patterns. The UVevis optical absorption spectrum of PCNHP shows the lower optical cut-off at w300 nm and the crystal was transparent in the entire visible region. The crystalline perfection of the grown crystal analysed by high-resolution X-ray diffraction (HRXRD) analysis reveals that the diffraction curve (DC) contains multi-peaks with low angular spread indicating the possibility of low angle structural grain boundaries. Scanning electron microscope (SEM) studies indicate the structure defect centers. The dielectric, thermal and mechanical behaviors of the specimen were also investigated. Crown Copyright Ó 2012 Published by Elsevier Masson SAS. All rights reserved.
Keywords: Intermetallic compounds Crystal growth High resolution X-ray diffraction Differential scanning calorimetry (DSC) Dielectric properties Mechanical properties
1. Introduction Crystals of phthalic acid derivatives are potential candidates for nonlinear optic and electro-optic processes. Acid phthalate crystals are crystallized as noncentrosymmetric or centrosymmetric structures depending on the nature of the cations, since in 3D crystallographic frame work the bonding orientation of growth unit is dramatically determined by these cations, on the basis of the chemical bonding theory of single crystal growth [1,2]. KHP possesses piezoelectric, pyroelectric, elastic and nonlinear optical properties [3e6]. It crystallizes in orthorhombic structure with space group Pca21 [7]. The influence of magnetic field on the microhardness of various metal phthalate crystals was reported by Koldaeva et al. [8]. The optical, dielectric, thermal properties [9] and structure [10] of lithium hydrogen phthalate have been investigated. It was observed that the second harmonic generation (SHG)
* Corresponding author. E-mail address: [email protected] (S.P. Meenakashisundaram).
efficiency of sodium hydrogen phthalate is double that of KHP crystals [11]. Single crystals of Sr(C8H5O4)2$2H2O were grown from an aqueous solution of SrCO3 and an excess of phthalic acid [12]. Structure of cesium(I) hydrogen phthalate reveals that Csþ cation is surrounded by eight O atoms [13] while Mg2þ cation is octahedrally coordinated in hexaaquamagnesium hydrogen phthalate [14]. Manganese dihydrogen diphthalate dihydrate crystallizes in the monoclinic space group P21/c [15]. The structures of [Co(H2O)6](C8H5O4)2 [16,17] and NiH2(C8O4H4)2$6H2O [18] consist of octahedrally coordinated cations [17]. Much structural work was performed on phthalate complexes of metal ions Tlþ$C8H5O 4 [19] and Rbþ$C8H5O 4 [20]. Influence of alkaline cation on the structure of polymeric o-phthalatocuprate(II) has been studied [21]. Molecular structures of magnesium di-o-phthalatocuprate(II) dihydrate and strontium di-o-phthalatocuprate(II) trihydrate [22] crystals consist of o-phthalatocuprate(II) complexes, joined in linear polymeric chains by bridging o-phthalate anions, of alkalineearth cations and of water molecules. Polymeric dihydroxydiphthalato tricobalt(II) crystallizes in orthorhombic space group Pccn [23]. Molecular structures of K2[Ni(H2O)6](C8H5O4)4$4H2O [24] and K2[Co(H2O)6](C8H5O4)4$4H2O have been reported [25].
1293-2558/$ e see front matter Crown Copyright Ó 2012 Published by Elsevier Masson SAS. All rights reserved. http://dx.doi.org/10.1016/j.solidstatesciences.2012.07.016
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K. Muthu et al. / Solid State Sciences 14 (2012) 1355e1360
Recently, we have investigated the influence of rare earth, alkaline earth and transition metals doping on the properties and crystalline perfection of KHP crystals [26,27]. It is interesting to observe that the alkaline earth metal Mg occupies predominantly substitutional positions while the transition metal Hg mainly occupies the interstitial sites. Also, accommodating capability of KHP crystals with dopants like Os(VIII) [28], Zn(II) [29] and sodium [30] revealing some interesting features has been analysed. In the present investigation, we report the growth, structure and crystalline perfection of a new mixed phthalate complex crystal. Influence of the impurities Co(II) and Ni(II) defecting the structure of KHP and the systematic analysis of the phthalate K2[Co(1x)Nix(H2O)6](C8H5O4)4$4H2O (x ¼ 0.25) by various characterization techniques have been detailed.
2. Experimental 2.1. Synthesis and crystal growth PCNHP was synthesized by dissolving the stoichiometric amounts (0.5:0.5:4.0) of AR grade cobalt(II) chloride haxahydrate (Qualigens), nickel(II) chloride hexahydrate (Qualigens) and potassium acid phthalate (Qualigens) in de-ionized water. Purified by recrystallization process using de-ionized water as solvent. Crystals were grown by slow evaporation solution growth technique. The crystallization took place within 15e16 days and the crystals were harvested when they attained an optimal size and shape. Photographs of as-grown PCNHP crystals are shown in Fig. 1.
Fig. 1. Photographs of as-grown PCNHP crystals.
2.2. Characterization The Fourier transform infrared (FT-IR) spectrum was recorded using AVATAR 330 FT-IR by the KBr pellet technique. A Bruker AXS (Kappa Apex II) X-ray diffractometer was used for single crystal Xray diffraction (XRD) studies. The powder X-ray diffraction was performed by using a Philips Xpert Pro Triple-axis X-ray diffractometer at room temperature using a wavelength of 1.540 Å and a step size of 0.008 . The samples were examined with CuKa radiation in a 2q range of 10e70 . The XRD data were analysed by the Rietveld method with RIETANe2000. To evaluate the crystalline perfection of the specimen crystals, HRXRD analysis was carried out. A multicrystal X-ray diffractometer developed at National Physical Laboratory (NPL), New Delhi [31] was used to record high-resolution diffraction curves (DCs). In this system, a fine focus (0.4 8 mm2; 2 kW Mo) X-ray source energized by a well-stabilized Philips X-ray generator (PW 1743) was employed. The well-collimated and monochromated MoKa1 beam obtained from the three monochromator Si crystals set in dispersive (þ,,) configuration has been used as the exploring X-ray beam. The DCs were recorded by changing the glancing angle (angle between the incident X-ray beam and the surface of the specimen) around the Bragg diffraction peak position qB (taken zero as reference point) starting from a suitable arbitrary glancing angle (q). Before recording the diffraction curve, to remove the non-crystallized solute atoms remained on the surface of the crystal and also to ensure the surface planarity, the specimens were first lapped and chemically etched in a nonpreferential etchant of water and acetone mixture in 1:2 volume ratio. The morphologies of the samples and the presence of dopants in the specimens were observed by using a JEOL JSM 5610 LV scanning electron microscope with a resolution of 3.0 nm and accelerating voltage 20 kV. The UVevisible transmittance spectrum was recorded using Hitachi UVevis spectrophotometer in the spectral range 200e800 nm. DSC analysis was carried out using SDT Q600 (TA instrument) thermal analyzer. Vickers microhardness was evaluated for the well polished grown crystal using Reichert 4000E Ultramicrohardness tester. Dielectric measurements were carried out by the parallel palate capacitor method as a function of temperature for various frequencies using a precision LCR meter (AGILENT 4284 A model).
Fig. 2. Powder XRD pattern of PCNHP crystal.
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3. Results and discussion
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Table 1 Crystal data of PCNHP single crystal.
3.1. X-ray diffraction analysis The powder XRD pattern of PCNHP crystal shows that the sample is of single phase without detectable impurity. Narrow peaks indicate the good crystallinity of the material. At room temperature all the observed reflections were indexed. The indexed powder XRD pattern of the as-grown PCNHP crystal is shown Fig. 2. The structure of PCNHP single crystal is analysed by single crystal XRD and the ORTEP diagram is given (Fig. 3). The chemical formula C16H20Co0.38KNi0.12O13 well supports the presence of Co(II) and Ni(II) in the crystalline matrix. It crystallizes in the monoclinic system with centrosymmetric space group P21/c and crystal data are given in the Table 1. The crystal structure consists of octahedral hexaaquacobalt cations, hexaaquanickel cations, Kþ ions, hydrogen o-phthalate anions and water molecules. The phthalate ions are connected in chains by short intermolecular hydrogen bonds. The Kþ ions are surrounded by oxygen atom and the Kþe O distance range is slightly higher in the case of mixed crystal (2.73(3)e3.28 (8) Å) in comparison with Ni(II) phthalate (2.67(9)e3.11(4)Å) and Co(II) phthalate (2.63(9)e3.24(4)Å) complexes. The MdOH2 distance range in the case of mixed crystal (2.04(2)e2.09(3) Å) is in close proximity with the reported values for Ni(II) phthalate (2.035(3)e2.072(3) Å) and Co(II) phthalate (2.05(2)e2.102(5) Å) complexes. The strongest hydrogen bond is observed between O1eH1dO7 (2.41 Å) and weak one for O10eH10 (B)dO2 (2.926 Å). 3.2. HRXRD analysis Fig. 4 shows the high-resolution rocking curve (RC) recorded for a typical PCNHP single crystal specimen using (200) diffracting planes in symmetrical Bragg geometry by employing the multicrystal X-ray diffractometer with MoKa1 radiation. As seen in the figure, the curve is not having a single diffraction peak. The solid
Chemical formula Chemical formula weight Unit cell parameters
Crystal size Volume Color Crystal system Space group Z Calculated density Radiation (l, Ǻ) Temperature
C16H20Co0.38 KNi0.12O13 488.86 g/mol a ¼ 10.4131(3)Ǻ b ¼ 6.8487(2)Ǻ c ¼ 29.4607(9)Ǻ b ¼ 98.064(10) 0.25 0.20 0.15 mm3 2080.25(11)Ǻ3 Black Monoclinic P21/c 4 1.561 g/cm3 MoKa (0.71073) 293 (2)K
line, which follows well with the experimental points (filled circles), is the convoluted curve of two peaks using the Lorentzian fit. On deconvolution of the diffraction curve, it is clear that the curve contains two additional peaks, which are 455 and 405 arc sec away from the central peak. These two additional peaks correspond to two internal structural low angle boundaries whose tilt angles are 455 and 405 arc sec from their adjoining regions. The FWHM (full width at half maximum) of the main peak and the boundaries are 204, 300 and 510 arc sec as depicted in the figure. The relatively high values of FWHM indicate that various regions (grains) of the crystal contains mosaic blocks which are misoriented to each other by at least a few tens of arc sec. Though the crystal contains a low angle boundary, the low angular spread of around 1200 arc sec (20 arc min) of the DC indicates that the quality of the crystal is fairly good. The influence of such defects may not influence much on the NLO properties. However, a quantitative analysis of such unavoidable defects is of great importance, particularly in case of phase matching applications as explained in our recent article [32].
Fig. 3. ORTEP diagram of PCNHP crystal.
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K. Muthu et al. / Solid State Sciences 14 (2012) 1355e1360 Table 2 FT-IR frequencies of some acid phthalate crystals. S.No
KHPa
LiHPb
NaHPc
PCNHP
Frequencies (cm1)
1 2 3 4 5 6
1090 1144 1445 1565 1675 3470
1072 1172 1401 1552 1685 3391
e e e e 1719 e
1079 1149 e 1551 1695 3375
nasOeHeO ns(OeHeO) nasOeC]O nsOeC]O ns(C]O) ns(OeH)
a b c
Ref. [6]. Ref. [9]. Ref. [11].
color precipitate confirms the presence of Ni(II). To another portion of the test solution dry ammonium thiocyanate crystals and amyl alcohol are added. The formation of the blue alcohol layer confirms the presence of cobalt(II). Fig. 4. HRXRD curve recorded for PCNHP crystal.
3.5. Optical transmission spectral analysis 3.3. FT-IR analysis The FT-IR spectrum (Fig. 5) of PCNHP crystal shows an absorption band in the region 500e900 cm1 due to CeH out of plane deformations of aromatic ring. The C]O stretching frequencies appeared at 1695 and 1640 cm1. The hydroxyl (eOH) stretching frequency appeared at 3375 cm1. The symmetric and asymmetric stretching frequencies of OeHeO appeared at 1149 and 1079 cm1. The characteristic vibrational patterns of some metal acid phthalates along with PCNHP crystal are given in Table 2.
The UVevis spectrum (Fig. 8) reveals that the cut-off wavelength is w300 nm. Absorption is minimum in the 300e800 nm region. Table 3 clearly reveals that the mixed crystal complex formation does not destroy the optical transmission. Because of high transparency, this specimen is quite useful for optical device applications. 3.6. Differential scanning calorimetry (DSC) The recorded DSC spectrum is shown in Fig. 9. The decomposition was recorded from 0 to 300 C. In the DSC curve, sharp
3.4. SEM and EDS analyses Scanning electron microscopic (SEM) study gives information about the surface nature and its suitability for device fabrication. Also it is used to check the presence of imperfections. The SEM pictures of PCNHP crystals at different magnifications are given in Fig. 6, indicating structure defect centers due to the incorporation of foreign metal ions. The presence of Co(II) and Ni(II) in the specimen was confirmed by EDS and it can be clearly seen in Fig. 7. Analysis of the surface at different sites reveals that the incorporation is non-uniform over the whole crystal surface. The presence of nickel and cobalt in the doped crystals is also established by a spot test. To a drop of the test solution (a portion of crystal dissolved in water) on a spot plate, a few drops of dilute dimethyl glyoxime solution and then a little aqueous ammonia solution are added. Development of rosy red
Fig. 5. FT-IR spectrum of PCNHP crystal.
Fig. 6. SEM photographs of PCNHP crystal.
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Fig. 7. Energy dispersive spectrum of PCNHP crystal.
Fig. 9. DSC curve of PCNHP crystal.
where P is the applied load in kg and d is the mean diagonal length of the indentation impression in micrometer. A plot of load (P) versus Vickers hardness number (Hv) exhibits that the hardness of the grown crystal increases as the load increases (Fig. 10). Cracks started developing around the indentation mark beyond a load of 100 g. This may be due to the internal stresses released during the indentation. The Mayer’s index number (n) or work hardening index is calculated and it is equal to 3.5, classifying PCNHP crystal to soft material category. 3.8. Dielectric studies
Fig. 8. UVeVis spectrum of PCNHP crystal.
endothermic peaks at 95 C and 107 C are due to liberation of water molecules. The endothermic peaks at 255 and 277 C could be due to the decomposition of residues.
Fig. 11(aec) is the plot of dielectric constant (3 r), dielectric loss (tan d) and AC conductivity (sac) versus temperature at different frequencies of as-grown PNHP crystals. It is observed that the dielectric constant and dielectric loss decrease with increase in frequency and attain saturation at higher frequencies. The AC electrical conductivity increases with increase in frequencies. This is the normal dielectric behavior of the materials. The large value of dielectric constant at low frequency and low temperature could be due to the presence of space charge polarizations which depend on
3.7. Mechanical studies Transparent crystals free from cracks were selected for microhardness measurements. Before indentations, the crystals were carefully lapped and washed to avoid surface effects. The Vickers hardness indentations were made on the as-grown surface of the PCNHP crystal at room temperature with the load ranging 25e100 g, keeping the time of indentations kept as 5 s for all trials. The Vickers hardness number Hv was calculated from the following equation,
Hv ¼ 1:8544 P=d2 kg=mm2 ;
Table 3 UV e cut e off some acid phthalate crystals. S.No
UV e cut e off (nm)
KHPa LiHPb NaHPc PCNHP
w300 w330 w320 w300
a b c
Ref. [6]. Ref. [9]. Ref. [11].
Fig. 10. The plot of Vickers hardness number (kg/mm2) versus load (g) for PCNHP crystal.
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[M(H2O)6]2þ (M ¼ Co(II)/Ni(II)) located between the anionic layers. The low dielectric constant at high frequency is indicative of a less defective good quality optical crystal. Acknowledgments The authors thank SAIF, IIT Madras, Chennai for providing single crystal XRD facility and Dr. C.K. Mahadevan, Physics Research Centre, S.T. Hindu College, Nagercoil for the support in dielectric studies. One of the authors, K. Muthu is thankful to CSIR, New Delhi, for the award of a Senior Research Fellowship. Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.solidstatesciences. 2012.07.016. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] Fig. 11. Dielectric measurements for PCNHP crystal. (a) Plot of dielectric constant vs temperature (K). (b) Plot of dielectric loss vs temperature (K). (c) Plot of AC electrical conductivity vs temperature (K).
[14] [15] [16]
the purity and perfection of the sample [33]. The increase in conductivity could be attributed to reduction in the space charge polarization at higher frequencies [34]. In the present study, dielectric constant varying proportionally with temperature is essentially due to the temperature variation of the polarizability [35]. The low dielectric loss at high frequency indicates that the asgrown crystal has good optical quality with lesser defects. The low 3 r value dielectric materials have potential applications in microelectronic industries.
[17]
4. Conclusions
[25]
A new phthalate complex crystal K2[Co(1x)Nix(H2O)6](C8H5O4)4$ 4H2O (x ¼ 0.25) has been synthesized and the solution growth from de-ionized water yielded the most perfect crystals in sizes of w20 13 4 mm3. Structural analysis by single crystal XRD analysis confirms the coexistence of Co(II) and Ni(II) in the complex and the presence of the metal in the product is supported by the EDS and chemical tests. DSC and FT-IR support the formation of the hydrated complex. Investigations reveal low cut-off wavelength, good transparency in the visible region, proportional increase of hardness with load and defect centered external morphology. Multi-peaks in HRXRD correspond to internal structural low angle grain boundaries which might be due to strains developed by the octahedral
[26]
[18] [19] [20] [21] [22] [23] [24]
[27] [28]
[29] [30] [31] [32] [33] [34] [35]
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