- Email: [email protected]
Ferroelectric properties of Sr doped hydroxyapatite bioceramics for biotechnological applications
Journal of Alloys and Compounds 689 (2016) 169e173
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Ferroelectric properties of Sr doped hydroxyapatite bioceramics for biotechnological applications Reem AL-Wafi Department of Physics, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 1 July 2016 Received in revised form 24 July 2016 Accepted 26 July 2016 Available online 28 July 2016
Electrical and dielectrical properties of strontium doped hydroxyapatite ceramics have been investigated by impedance and ferroelectric spectroscopy. SEM, FTIR and EDS techniques were used to analyze the chemical and structural properties of Sr doped HaP ceramics. The structural analysis shows that the particles size of HaP and Sr doped biomaterials are in the range of nanometer, i.e., the biomaterials are nanomaterials. Sr doping changes the particle distribution and particle size of HaP samples. The dielectric constants of the ceramics are significantly changed with Sr doping. The polarization vs electric fields plots indicate that Sr doped HaP samples are ferroelectric materials. It is evaluated that the ferroelectric properties of hydroxyapatite is controlled by Sr doping. © 2016 Elsevier B.V. All rights reserved.
Keywords: Ceramics Ferroelectric Sol gel method
1. Introduction
2. Materials and method
One of advanced materials is biomaterials which have been extensively investigated for biotechnological applications in recent years. The functional properties of these materials can be improved by nanosize for various applications [1]. The apatites are one group of biomaterials used for biotechnological applications [2e4]. The hydroxyapatite (HAp), Ca10(PO4)6(OH)2 is one of calcium phosphate (CaP) ceramics [5,6]. The HaP which has a good a biocompatibility and bioactivity is an important material for bone repairing [7,8]. This material is promising material for biotechnological applications [9e11]. The biological response of HaP is related to electric polarization to manipulate biomedical tissues [12e15]. The electrical polarization is related to dielectric parameters. The dielectric constants of HaP can be improved by various metal ion contents. The improved dielectric and ferroelectric properties of HaP are pertinent to orthopedic and dental applications, etc. [16,17]. In present study, we synthesized nanostructured hydroxyapatite by sol gel method. We have controlled the dielectrical and ferroelectric properties for biotechnological applications. The synthesis and dielectric properties of Sr doped HaP samples were investigated in detail.
The strontium (Sr) doped hydroxyapatite (HaP) samples were prepared using the calcium nitrate tetrahydrate (Ca(NO3)2$4H2O) and diammonium hydrogen phosphate ((NH4)2HPO4) and strontium acetate. The Sr doped HaP samples were doped for various x ratios (x ¼ 0.1, 0.2, 0.3, 0.4 and 0.5). Firstly, the calcium nitrate tetrahydrate (Ca(NO3)2$4H2O) with nominal value was dissolved in deionized water and stirred for 10 min. Afterwards, the pH of the solution was set to 8 by adding ammonia and the diammonium hydrogen phosphate was added to the solution and stirred for 2 h at 80 C. Sr doped HaP solutions were prepared with the same procedure. The gel solutions of the samples were dried at 100 C for 12 h. The obtained powder samples were calcinated at 800 C for 2 h. the dielectric constants and alternating current conductivity (AC) were measured using a HIOKI LCR meter. The polarizationvoltage measurements were performed using a Radiant ferroelectric tester. A Nicolet FTIR spectrophotometer was used to obtain FTIR spectra of the samples. The structural properties of the samples were investigated by JEOL electron microscope. 3. Results and discussion 3.1. Structural properties of Sr doped HaP ceramics
E-mail address: [email protected]. http://dx.doi.org/10.1016/j.jallcom.2016.07.285 0925-8388/© 2016 Elsevier B.V. All rights reserved.
FTIR spectra of Sr doped HaP samples are shown in Fig. 1.As seen in Fig. 1, the observed bands in FTIR spectra corresponds the bands confirming the chemical structure of the samples. The observed
170
R. AL-Wafi / Journal of Alloys and Compounds 689 (2016) 169e173
Transmittance (a.u)
100 80 HaP x=0.2 x=0.3 x=0.4 x=0.5
60 40 20 0 1000
2000 3000 Wavenumbers (cm-1)
4000
Fig. 1. FTIR spectra of Sr doped HaP ceramics.
bands are the bands of hydroxyl and absorbed water phosphate species. The band observed at 3572 cm1 is related to hydroxyl stretching mode. At 903e962 cm1, n1 stretching mode of PO3 4 group was observed while n3 stretching mode was observed at 1032e1092 cm1 [18,19]. For the samples, OH and PO4 bands was observed at 550 cm1e650 cm1 and 1091e962 cm1, respectively. The presence of these bands confirms the formation of HAp and aTCP structures. The peak intensity of the bands at 560 cm1e600 cm1 is decreased with Sr doping. This confirms that the substitution of Sr into structure of HaP. The phosphate group was observed with the presence of the bands at 1020 cm1 and 1100 cm1 [16,17]. The chemical structure of HAp samples were confirmed with the observed bands in FTIR spectra confirmed [19]. The scanning electron microscopy images of Sr doped hydroxyapatite samples are shown in Fig. 2. As seen in Fig. 2, the particles size of HaP was found to be in the range of 40e72 nm. This indicates that the particle size of HaP is in the nanosize region. The particle size is changed with Sr doping. The particle size distribution of HaP is controlled by Sr doping. It is evaluated that the Sr doping change both particle size and distribution of particles in HaP. We used X-ray Energy Dispersive spectroscopy (EDS) to confirm the chemical composition of the HaP. For this, we got EDS spectrum of HaP. It is seen in Fig. 3 that the HaP included phosphorus, calcium and oxygen, while Sr doped HaP samples included phosphorus, calcium, and oxygen and strontium elements. The ratio of calcium to phosphorus was found to 1.67 and we gave only one spectra for HaP sample. In order to determine the crystal structures of the samples, we employed X-ray diffraction technique and XRD patterns of the Sr doped HaP samples are shown in Fig. 4. XRD patterns were analyzed and all patterns confirm the hexagonal phase with the space group of P63/m and cell constants a ¼ b ¼ 9.4240 Å, and c ¼ 6.8790 Å (JCPDS: 74e0565). In undoped HaP, b-TCP peak was observed and the intensity of this peak is decreased and disappeared. This change indicates the substitution of Sr with Ca ion the hydroxyapatite structure.
3.2. Dielectric properties of Sr doped hydroxyapatite ceramics We analyzed the dielectric relaxation mechanism of the ceramics using the dielectric spectroscopy. The real and imaginary parts of the complex dielectric constants for the samples are shown in Fig. 5. The dielectric constant and dielectric loss dependence of
frequency means that the dielectric parameters of the ceramics are dispersive. As seen in Fig. 5, the dielectric constants of the ceramics are changed with Sr dopant. The change in the dielectric constant is due to the electrical polarization which is controlled by Sr dopant. The doping of Sr into HaP changes the electrical polarization and in turn, the dipole moments in HaP. These moments are oscillated with applied electric field. As seen in Fig. 5, at the lower frequencies, the dielectric constant of the HaP was about 10. After the doping for x ¼ 0.2, it is decreases and after x ¼ 0.3 doping, it increases with Sr content. The obtained εr of HaP is close to the dielectric constant obtained by another methods [20,21]. Fig. 6 shows the dielectric loss factor,εi, of Sr doped ceramics. The imaginary part of the dielectric constant increases with frequency and exhibited a dielectric relaxation peak and its position is shifted to the higher frequencies with Sr doping. The relaxation mechanism of the Sr doped ceramics was analyzed by Cole-Cole analysis and Cole-Cole plots are shown in Fig. 7. The plots of εr vs εi gives two semicircles with the various diameters. It is seen in Fig. 7 that the diameter of Cole-Cole curves is changed with Sr doping. The plotted Cole-Col curves were analyzed by the following relation,
ε* ðuÞ ¼ ε∞ þ
εs ε∞
1 þ ðjutÞ1a
(1)
where ε*(u) is the complex dielectric function, ε∞ and εo are the high and low frequency limiting dielectric constants, respectively, t is the relaxation time and a is the distribution parameter determining the dielectric relaxation mechanism. The a values for Sr doped ceramics were determined from Cole-Cole curves and the obtained a values indicates that the ceramics exhibited a nonDebye type dielectric relaxation mechanism. 3.3. AC conductivity properties of Sr doped HaP ceramics The alternating current conductivity (AC) of Sr doped ceramics are shown in Fig. 8. It is seen in Fig. 8 that the AC conductivity increases linearly with frequency and it does not exhibit a direct current conductivity. This confirms that the Sr doped HaP ceramics exhibited an insulator behavior. The insulator conduction mechanism of the ceramics can be analyzed by the following relation [22,23].
sðf Þ ¼ so f n
(2)
Where f is the frequency, so is a constant, and n is an exponent. In order to analyze the conduction mechanism, we should find n value from AC conductivity plot. The n value for the ceramics were found to be about 1.0. The obtained n value indicates that monolinear AC conduction mechanism is taking place in the Sr doped HaP ceramics. Also, we analyzed the DC conduction mechanism with electric resistance measurement. We obtained ~1011 S/cm electrical conductivity of Sr doped ceramics. This also confirms that the Sr doped ceramics are insulator materials and they do not include free electrons.Fig. 8 3.4. Ferroelectric properties of Sr doped HaP ceramics We analyzed the ferroelectric behavior of the ceramics, because this property is related the electric polarization. The electric polarization behavior is related the polarized surface as biological response for biomedical applications. For this, we measured the polarization versus electric field (PeE) hysteresis curves and are shown in Fig. 9. The polarization plots exhibited the ferroelectric loops and the shape of the loops is changed with Sr content. The
R. AL-Wafi / Journal of Alloys and Compounds 689 (2016) 169e173
171
Fig. 2. SEM images of Sr doped HaP ceramics. a) x ¼ 0 b) x ¼ 0.2 c) x ¼ 0.3 d) x ¼ 04 e) x ¼ 0.5.
polarization is decreased with Sr doping except for x ¼ 0.3. It is seen that the polarization is increased highly for x ¼ 0.3 ratio. It is evaluated that this ratio is optimum value for ferroelectric behavior of the Sr doped HaP ceramics. The decrease or increase in electric polarization of the Sr doped HaP ceramics is related to electric dipole which controls the polarization of the ceramics. The polarization curves exhibited a remnant polarization, Pr and coercive field and these parameters are changed with Sr content. Sr doped HaP ceramic having x ¼ 0.3 ratio exhibited the high electric polarization as well as doped samples. The lowest polarization was observed for x ¼ 0.5 content. It is evaluated that the electric polarization of HaP can be increased or decreased with optimum Sr content. 4. Conclusions Fig. 3. EDS spectra of HAp ceramic.
Sr doped HaP ceramics were synthesized by sol gel method. The dielectric constant and ferroelectric behavior of the ceramics were
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R. AL-Wafi / Journal of Alloys and Compounds 689 (2016) 169e173
Fig. 4. XRD patterns of Sr doped HaP ceramics.
Fig. 7. Cole-Cole plots of Sr doped HaP ceramics.
Fig. 5. Plots of ε0 vs. f of Sr doped HaP ceramics.
Fig. 8. AC plots of Sr doped HaP ceramics.
Fig. 6. Plots of ε00 vs. f of Sr doped HaP ceramics.
Fig. 9. Polarization-electric field (PeE) hysteresis curves of Sr doped HaP ceramics.
R. AL-Wafi / Journal of Alloys and Compounds 689 (2016) 169e173
analyzed in detail. The synthesized ceramics exhibited the ferroelectric behavior. Cole-Cole plots suggest that a non-Debye dielectric relaxation mechanism is dominant in the ceramics. Sr content controls the dielectric and ferroelectric properties and it is evaluated that these ceramics can be used for dielectric device applications. References [1] Omar A. Al-Hartomy, Ahmed A. Al-Ghamdi, M.M. El-Desoky, Farid El-Tantawy, W.A. Farooq, Grain-Size Effects on the Structural and Electrical Properties of IroneBased Nano-Crystalline Glass-Ceramic, Journal of Materials and Electronic Devices 1 (2016) 24e29. [2] A. Ito, H. Aoki, M. Akao, N. Miura, R. Otsuka, S. Tsutsumi, Flux growth and crystal structure of boron-containing apatite, J. Ceram. Soc. Jpn. 96 (1988) 305e309. [3] R. Ternane, M. Th Cohen-Adad, G. Panczer, C. Goutaudier, C. Dujardin, G. Boulon, N. Kbir-Ariguib, M. Trabelsi-Ayedi, Structural and luminescent properties of new Ce3þ doped calcium borophosphate with apatite structure, Solid State Sci. 4 (2002) 53e59. [4] S. Barheine, S. Hayakawa, A. Osaka, C. Jaeger, Surface, interface, and bulk structure of borate containing apatitic biomaterials, Chem. Mater. 21 (2009) 3102e3109. [5] L.C. Chow, Next generation calcium phosphate-based biomaterials, Dent. Mater. J. 28 (2009) 1e10. [6] R.Z. LeGeros, J.P. LeGeros, Hydroxyapatite (Chapter 16), in: T. Kokubo (Ed.), Bioceramics and their Clinical Applications, Woodhead Publishing Limited, Cambridge, U.K, 2008, pp. 367e394. [7] M.H. Fathi, A. Hanifi, Evaluation and characterization of nanostructure hydroxyapatite powder prepared by simple solegel method, Mater. Lett. 61 (2007) 3978e3983. [8] M.H. Fathi, A. Hanifi, V. Mortazavi, Preparation and bioactivity evaluation of bone likehydroxyapatite nanopowder, J. Mater. Process. Technol. 202 (2008) 536e542. [9] O. Korostynska, A.A. Gandhi, A. Mason, A. Al-Shamma'a, S.A.M. Tofail, Biomedical sensing with hydroxyapatite ceramics in GHz frequency range, Key Eng. Mater. 543 (2013) 26e29.
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[10] S. Tarafder, S. Banerjee, A. Bandyopadhyay, S. Bose, Electrically polarized biphasic calcium phosphates: adsorption and release of bovine serum albumin, Langmuir 26 (2010) 16625e16629. [11] R.U. Mene, M.P. Mahabole, K.C. Mohite, R.S. Khairnar, Improved gas sensing and dielectric properties of Fe doped hydroxyapatite thick films: effect of molar concentrations, Mater. Res. Bull. (50) (2014) 227e234. [12] M. Nakamura, A. Nagai, Y. Tanaka, Y. Sekijima, K. Yamashita, Polarized hydroxyapatite promotes spread and motility of osteoblastic cells, J. Biomed. Mater. Res. Part A 92 (2010) 783e790. [13] M. Nakamura, A. Nagai, T. Okura, Y. Sekijima, T. Hentunen, K. Yamashita, Enhanced osteoblastic adhesion through improved wettability on polarizedhydroxyapatite, J. Ceram. Soc. Jpn. 118 (2010) 474e478. [14] T. Kobayashi, S. Nakamura, K. Yamashita, Enhanced osteobonding by negative surface charges of electrically polarized hydroxyapatite, J. Biomed. Mater. Res. 57 (2001) 477e484. [15] S. Itoh, S. Nakamura, M. Nakamura, K. Shinomiya, K. Yamashita, Enhanced bone regeneration by electrical polarization of hydroxyapatite, Artif. Organs (30) (2006) 863e869. [16] T.J. Webster, C. Ergun, R.H. Doremus, R. Bizios, Hydroxylapatite with substituted magnesium, zinc, cadmium, and yttrium. II. Mechanisms of osteoblast adhesion, J. Biomed. Mater. Res. 59 (2002) 312e317. [17] M. Sato, M.A. Sambito, A. Aslani, N.M. Kalkhoran, E.B. Slamovich, T.J. Webster, Increased osteoblast functions on undoped and yttrium- doped nanocrystalline hydroxyapatite coatings on titanium, Biomaterials 27 (2006) 2358e2369. [18] C. Zhang, C. Li, S. Huang, Z. Hou, Z. Cheng, P. Yang, C. Peng, J. Lin, Biomaterials 31 (2010) 3374e3383. [19] V. Stanica, S. Dimitrijevic, J. Antic-Stankovic, M. Mitric, B. Jokic, I.B. Plecas, S. Raicevic, Appl. Surf. Sci. 256 (2010) 6083e6089. [20] Ashutosh K. Dubey 1, P.K. Mallik 1, S. Kundu, B. Basu, J. Eur. Ceram. Soc. 33 (2013) 3445e3453. [21] Ravindra U. Mene, Megha P. Mahabole, K.C. Mohite, Rajendra S. Khairnar, Mater. Res. Bull. 50 (2014) 227e234. [22] P. Muralidharan, M. Venkateswarlu, N. Satyanarayana, AC conductivity studies of lithium borosilicate glasses: synthesized by solegel process with various concentrations of nitric acid as a catalyst, Mater. Chem. Phys. 88 (2004) 138e144. [23] S. Mahboob, G. Prasad, G.S. Kumar, Impedance and a.c. conductivity studies on Ba(Nd02Ti06Nb02)O3 ceramic prepared through conventional and microwave sintering route, Bull. Mater. Sci. (29) (2006) 347e355.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Ferroelectric properties of Sr doped hydroxyapatite bioceramics for biotechnological applications Reem AL-Wafi Department of Physics, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 1 July 2016 Received in revised form 24 July 2016 Accepted 26 July 2016 Available online 28 July 2016
Electrical and dielectrical properties of strontium doped hydroxyapatite ceramics have been investigated by impedance and ferroelectric spectroscopy. SEM, FTIR and EDS techniques were used to analyze the chemical and structural properties of Sr doped HaP ceramics. The structural analysis shows that the particles size of HaP and Sr doped biomaterials are in the range of nanometer, i.e., the biomaterials are nanomaterials. Sr doping changes the particle distribution and particle size of HaP samples. The dielectric constants of the ceramics are significantly changed with Sr doping. The polarization vs electric fields plots indicate that Sr doped HaP samples are ferroelectric materials. It is evaluated that the ferroelectric properties of hydroxyapatite is controlled by Sr doping. © 2016 Elsevier B.V. All rights reserved.
Keywords: Ceramics Ferroelectric Sol gel method
1. Introduction
2. Materials and method
One of advanced materials is biomaterials which have been extensively investigated for biotechnological applications in recent years. The functional properties of these materials can be improved by nanosize for various applications [1]. The apatites are one group of biomaterials used for biotechnological applications [2e4]. The hydroxyapatite (HAp), Ca10(PO4)6(OH)2 is one of calcium phosphate (CaP) ceramics [5,6]. The HaP which has a good a biocompatibility and bioactivity is an important material for bone repairing [7,8]. This material is promising material for biotechnological applications [9e11]. The biological response of HaP is related to electric polarization to manipulate biomedical tissues [12e15]. The electrical polarization is related to dielectric parameters. The dielectric constants of HaP can be improved by various metal ion contents. The improved dielectric and ferroelectric properties of HaP are pertinent to orthopedic and dental applications, etc. [16,17]. In present study, we synthesized nanostructured hydroxyapatite by sol gel method. We have controlled the dielectrical and ferroelectric properties for biotechnological applications. The synthesis and dielectric properties of Sr doped HaP samples were investigated in detail.
The strontium (Sr) doped hydroxyapatite (HaP) samples were prepared using the calcium nitrate tetrahydrate (Ca(NO3)2$4H2O) and diammonium hydrogen phosphate ((NH4)2HPO4) and strontium acetate. The Sr doped HaP samples were doped for various x ratios (x ¼ 0.1, 0.2, 0.3, 0.4 and 0.5). Firstly, the calcium nitrate tetrahydrate (Ca(NO3)2$4H2O) with nominal value was dissolved in deionized water and stirred for 10 min. Afterwards, the pH of the solution was set to 8 by adding ammonia and the diammonium hydrogen phosphate was added to the solution and stirred for 2 h at 80 C. Sr doped HaP solutions were prepared with the same procedure. The gel solutions of the samples were dried at 100 C for 12 h. The obtained powder samples were calcinated at 800 C for 2 h. the dielectric constants and alternating current conductivity (AC) were measured using a HIOKI LCR meter. The polarizationvoltage measurements were performed using a Radiant ferroelectric tester. A Nicolet FTIR spectrophotometer was used to obtain FTIR spectra of the samples. The structural properties of the samples were investigated by JEOL electron microscope. 3. Results and discussion 3.1. Structural properties of Sr doped HaP ceramics
E-mail address: [email protected]. http://dx.doi.org/10.1016/j.jallcom.2016.07.285 0925-8388/© 2016 Elsevier B.V. All rights reserved.
FTIR spectra of Sr doped HaP samples are shown in Fig. 1.As seen in Fig. 1, the observed bands in FTIR spectra corresponds the bands confirming the chemical structure of the samples. The observed
170
R. AL-Wafi / Journal of Alloys and Compounds 689 (2016) 169e173
Transmittance (a.u)
100 80 HaP x=0.2 x=0.3 x=0.4 x=0.5
60 40 20 0 1000
2000 3000 Wavenumbers (cm-1)
4000
Fig. 1. FTIR spectra of Sr doped HaP ceramics.
bands are the bands of hydroxyl and absorbed water phosphate species. The band observed at 3572 cm1 is related to hydroxyl stretching mode. At 903e962 cm1, n1 stretching mode of PO3 4 group was observed while n3 stretching mode was observed at 1032e1092 cm1 [18,19]. For the samples, OH and PO4 bands was observed at 550 cm1e650 cm1 and 1091e962 cm1, respectively. The presence of these bands confirms the formation of HAp and aTCP structures. The peak intensity of the bands at 560 cm1e600 cm1 is decreased with Sr doping. This confirms that the substitution of Sr into structure of HaP. The phosphate group was observed with the presence of the bands at 1020 cm1 and 1100 cm1 [16,17]. The chemical structure of HAp samples were confirmed with the observed bands in FTIR spectra confirmed [19]. The scanning electron microscopy images of Sr doped hydroxyapatite samples are shown in Fig. 2. As seen in Fig. 2, the particles size of HaP was found to be in the range of 40e72 nm. This indicates that the particle size of HaP is in the nanosize region. The particle size is changed with Sr doping. The particle size distribution of HaP is controlled by Sr doping. It is evaluated that the Sr doping change both particle size and distribution of particles in HaP. We used X-ray Energy Dispersive spectroscopy (EDS) to confirm the chemical composition of the HaP. For this, we got EDS spectrum of HaP. It is seen in Fig. 3 that the HaP included phosphorus, calcium and oxygen, while Sr doped HaP samples included phosphorus, calcium, and oxygen and strontium elements. The ratio of calcium to phosphorus was found to 1.67 and we gave only one spectra for HaP sample. In order to determine the crystal structures of the samples, we employed X-ray diffraction technique and XRD patterns of the Sr doped HaP samples are shown in Fig. 4. XRD patterns were analyzed and all patterns confirm the hexagonal phase with the space group of P63/m and cell constants a ¼ b ¼ 9.4240 Å, and c ¼ 6.8790 Å (JCPDS: 74e0565). In undoped HaP, b-TCP peak was observed and the intensity of this peak is decreased and disappeared. This change indicates the substitution of Sr with Ca ion the hydroxyapatite structure.
3.2. Dielectric properties of Sr doped hydroxyapatite ceramics We analyzed the dielectric relaxation mechanism of the ceramics using the dielectric spectroscopy. The real and imaginary parts of the complex dielectric constants for the samples are shown in Fig. 5. The dielectric constant and dielectric loss dependence of
frequency means that the dielectric parameters of the ceramics are dispersive. As seen in Fig. 5, the dielectric constants of the ceramics are changed with Sr dopant. The change in the dielectric constant is due to the electrical polarization which is controlled by Sr dopant. The doping of Sr into HaP changes the electrical polarization and in turn, the dipole moments in HaP. These moments are oscillated with applied electric field. As seen in Fig. 5, at the lower frequencies, the dielectric constant of the HaP was about 10. After the doping for x ¼ 0.2, it is decreases and after x ¼ 0.3 doping, it increases with Sr content. The obtained εr of HaP is close to the dielectric constant obtained by another methods [20,21]. Fig. 6 shows the dielectric loss factor,εi, of Sr doped ceramics. The imaginary part of the dielectric constant increases with frequency and exhibited a dielectric relaxation peak and its position is shifted to the higher frequencies with Sr doping. The relaxation mechanism of the Sr doped ceramics was analyzed by Cole-Cole analysis and Cole-Cole plots are shown in Fig. 7. The plots of εr vs εi gives two semicircles with the various diameters. It is seen in Fig. 7 that the diameter of Cole-Cole curves is changed with Sr doping. The plotted Cole-Col curves were analyzed by the following relation,
ε* ðuÞ ¼ ε∞ þ
εs ε∞
1 þ ðjutÞ1a
(1)
where ε*(u) is the complex dielectric function, ε∞ and εo are the high and low frequency limiting dielectric constants, respectively, t is the relaxation time and a is the distribution parameter determining the dielectric relaxation mechanism. The a values for Sr doped ceramics were determined from Cole-Cole curves and the obtained a values indicates that the ceramics exhibited a nonDebye type dielectric relaxation mechanism. 3.3. AC conductivity properties of Sr doped HaP ceramics The alternating current conductivity (AC) of Sr doped ceramics are shown in Fig. 8. It is seen in Fig. 8 that the AC conductivity increases linearly with frequency and it does not exhibit a direct current conductivity. This confirms that the Sr doped HaP ceramics exhibited an insulator behavior. The insulator conduction mechanism of the ceramics can be analyzed by the following relation [22,23].
sðf Þ ¼ so f n
(2)
Where f is the frequency, so is a constant, and n is an exponent. In order to analyze the conduction mechanism, we should find n value from AC conductivity plot. The n value for the ceramics were found to be about 1.0. The obtained n value indicates that monolinear AC conduction mechanism is taking place in the Sr doped HaP ceramics. Also, we analyzed the DC conduction mechanism with electric resistance measurement. We obtained ~1011 S/cm electrical conductivity of Sr doped ceramics. This also confirms that the Sr doped ceramics are insulator materials and they do not include free electrons.Fig. 8 3.4. Ferroelectric properties of Sr doped HaP ceramics We analyzed the ferroelectric behavior of the ceramics, because this property is related the electric polarization. The electric polarization behavior is related the polarized surface as biological response for biomedical applications. For this, we measured the polarization versus electric field (PeE) hysteresis curves and are shown in Fig. 9. The polarization plots exhibited the ferroelectric loops and the shape of the loops is changed with Sr content. The
R. AL-Wafi / Journal of Alloys and Compounds 689 (2016) 169e173
171
Fig. 2. SEM images of Sr doped HaP ceramics. a) x ¼ 0 b) x ¼ 0.2 c) x ¼ 0.3 d) x ¼ 04 e) x ¼ 0.5.
polarization is decreased with Sr doping except for x ¼ 0.3. It is seen that the polarization is increased highly for x ¼ 0.3 ratio. It is evaluated that this ratio is optimum value for ferroelectric behavior of the Sr doped HaP ceramics. The decrease or increase in electric polarization of the Sr doped HaP ceramics is related to electric dipole which controls the polarization of the ceramics. The polarization curves exhibited a remnant polarization, Pr and coercive field and these parameters are changed with Sr content. Sr doped HaP ceramic having x ¼ 0.3 ratio exhibited the high electric polarization as well as doped samples. The lowest polarization was observed for x ¼ 0.5 content. It is evaluated that the electric polarization of HaP can be increased or decreased with optimum Sr content. 4. Conclusions Fig. 3. EDS spectra of HAp ceramic.
Sr doped HaP ceramics were synthesized by sol gel method. The dielectric constant and ferroelectric behavior of the ceramics were
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R. AL-Wafi / Journal of Alloys and Compounds 689 (2016) 169e173
Fig. 4. XRD patterns of Sr doped HaP ceramics.
Fig. 7. Cole-Cole plots of Sr doped HaP ceramics.
Fig. 5. Plots of ε0 vs. f of Sr doped HaP ceramics.
Fig. 8. AC plots of Sr doped HaP ceramics.
Fig. 6. Plots of ε00 vs. f of Sr doped HaP ceramics.
Fig. 9. Polarization-electric field (PeE) hysteresis curves of Sr doped HaP ceramics.
R. AL-Wafi / Journal of Alloys and Compounds 689 (2016) 169e173
analyzed in detail. The synthesized ceramics exhibited the ferroelectric behavior. Cole-Cole plots suggest that a non-Debye dielectric relaxation mechanism is dominant in the ceramics. Sr content controls the dielectric and ferroelectric properties and it is evaluated that these ceramics can be used for dielectric device applications. References [1] Omar A. Al-Hartomy, Ahmed A. Al-Ghamdi, M.M. El-Desoky, Farid El-Tantawy, W.A. Farooq, Grain-Size Effects on the Structural and Electrical Properties of IroneBased Nano-Crystalline Glass-Ceramic, Journal of Materials and Electronic Devices 1 (2016) 24e29. [2] A. Ito, H. Aoki, M. Akao, N. Miura, R. Otsuka, S. Tsutsumi, Flux growth and crystal structure of boron-containing apatite, J. Ceram. Soc. Jpn. 96 (1988) 305e309. [3] R. Ternane, M. Th Cohen-Adad, G. Panczer, C. Goutaudier, C. Dujardin, G. Boulon, N. Kbir-Ariguib, M. Trabelsi-Ayedi, Structural and luminescent properties of new Ce3þ doped calcium borophosphate with apatite structure, Solid State Sci. 4 (2002) 53e59. [4] S. Barheine, S. Hayakawa, A. Osaka, C. Jaeger, Surface, interface, and bulk structure of borate containing apatitic biomaterials, Chem. Mater. 21 (2009) 3102e3109. [5] L.C. Chow, Next generation calcium phosphate-based biomaterials, Dent. Mater. J. 28 (2009) 1e10. [6] R.Z. LeGeros, J.P. LeGeros, Hydroxyapatite (Chapter 16), in: T. Kokubo (Ed.), Bioceramics and their Clinical Applications, Woodhead Publishing Limited, Cambridge, U.K, 2008, pp. 367e394. [7] M.H. Fathi, A. Hanifi, Evaluation and characterization of nanostructure hydroxyapatite powder prepared by simple solegel method, Mater. Lett. 61 (2007) 3978e3983. [8] M.H. Fathi, A. Hanifi, V. Mortazavi, Preparation and bioactivity evaluation of bone likehydroxyapatite nanopowder, J. Mater. Process. Technol. 202 (2008) 536e542. [9] O. Korostynska, A.A. Gandhi, A. Mason, A. Al-Shamma'a, S.A.M. Tofail, Biomedical sensing with hydroxyapatite ceramics in GHz frequency range, Key Eng. Mater. 543 (2013) 26e29.
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