THE EFFECT OF Nd SUBSTITUTION ON THE GLASS FORMING ABILITY AND THERMAL PROPERTIES IN THE SYSTEM Bi 2

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1 Stanislav Journal of Slavov Chemical Elena Technology Kashchieva and Svetlin Metallurgy Parvanov 50 4 Yanko 2015 Dimitriev THE EFFECT OF Nd SUBSTITUTION ON THE GLASS FORMING ABILITY AND THERMAL PROPERTIES IN THE SYSTEM Bi 2 Stanislav Slavov 1 Elena Kashchieva 1 Svetlin Parvanov 1 Yanko Dimitriev 2 1 Department of Physics University of Chemical Technology and Metallurgy 8 Kl Ohridski 1756 Sofia Bulgaria stanislavslavov@hotmailcom 2 Department of Silicate Technology University of Chemical Technology and Metallurgy 8 Kl Ohridski Blvd 1756 Sofia Bulgaria Received 15 January 2015 Accepted 23 April 2015 ABSTRACT The paper reports data on glass formation in wider concentration ranges The samples amorphous nature is characterized by x-ray diffraction analysis their thermal characteristics and stability are determined by differential thermal analysis (DTA) while the transmission and absorption characteristics outlined are investigated by ultraviolet-visible spectroscopy (UV-Vis) SiO 2 content increase leads to a shift of the absorption border to lower wavelengths The experimental results show that it is possible to obtain low-melting glasses containing 5 mol % - 20 mol % SiO 2 and 30 mol % - 63 mol % Bi 2 with the synthesis technique applied Substitution of Bi 2 with Nd 2 up to 10 mol% leads to the preparation of a complex multicomponent glasses and glass-crystalline materials of high thermal stability Keywords: bismuth titanate ceramics melt quenching Nd substitution INTRODUCTION This study is a continuation of the previous one referring to glass-formation and crystallization of samples of the system Bi 2 [1-5] The motivation for such research is to receive a new generation on bismuth-titanate based materials with perspective electrical properties that have been shown to be highly dependent on the method of preparation [6-13] The basic method used by us up to now is that of the super-cooled melt which provides to modify the microstructure texture size and morphology of crystals the type and amount of crystalline phases The successful implementation of the method however requires to clarify the suitable conditions of synthesis The aim of this work is to investigate phase-formation of samples in the system Bi 2 where Nd 2 content varies in a narrow concentration range - from 8 mol % to 10 mol % The choice of the system components is based on data for Bi 2 and TiO 2 which are the basis for obtaining of silenites Auriuvilius and pirohloric phases On the other hand SiO 2 which is a traditional glass former is introduced in a limited amount (5 mol % to 20 mol %) This is required to correct the trend of amorphizing but not the materials electric properties Plasing Nd 2 is useful to modify the electrical properties and improve the thermal stability of the samples [14-17] EXPERIMENTAL The preparation of samples in the system Bi 2 - TiO 2 was carried out by the method of supecooled melt with a cooling rate of 10 2 K s -1 The raw materials were Bi 2 (Alfa Aesar 9999 %) ТiO 2 (Alfa Aesar 9995 %) SiO 2 (Alfa Aesar 9995 %) and Nd 2 (Alfa Aesar 9999 %) They were mixed and homogenized for 15 min The melting was carried out 435

2 Journal of Chemical Technology and Metallurgy in alumina crucibles in two stages: with temperatures retention at 1150 C and 1450 C respectively and rapid cooling to room temperature The selected temperatures were determined by the nominal composition and data from the phase diagrams of the studied system [18-20] The resulting materials were characterized by X-ray phase analysis XRD - TUR M62 Cu-Kα Differential thermal analysis Setaram Labsys Evo 1600 (10 degrees per minute) UV-Vis spectrometer Cary 100 version 900 and an optical microscope Bresser DigiMicroscope DM 400 The conditions of melting and the results of visual and phase characterization are summarized in Table 1 RESULTS AND DISCUSSION The microscopic observations at various magnifications (80x 350x) illustrated in Fig 1 are used to characterize the microstructure Compositions (4 4A 4B) which are visually characterized as amorphous and transparent are shown as an example The X-Ray diffractogams (Fig 2) indicate that different phases are obtained depending on the nominal composition: 1) glass-ceramic samples involving one phase - Bi 4 (Bi 4-x ) (4 and 4D); 2) polyphase samples involving Bi 4 (Bi 4-x ) и δ-bi 2 (4C и 4E) and 3) vitreous samples (4A and 4B) The diffractograme of sample e of a composition in mole percent 60Bi 2 20TiO 2 is shown for comparison It is characterized by crystallization of Bi 12 TiO 20 phase in an amorphous matrix It is evident that the introduction of Nd 2 in 4A and 4B does not induce crystallization but even improves amorphization The samples are characterized by different thermal behavior (Fig 3) Composition 4 which contains 50 mol % TiO 2 is characterized by Tg = 632 о C and a single peak of crystallization at ca 660 о C The softening temperature of other samples of low TiO 2 content (16 mol % - 18 mol %) lowered to 476 о C Several exothermic effects are also detected in case of crystallization at 557 о C 631 о C 691 о C 769 о C This result is consistent with XRD analysis of the samples where several crystalline phases are identified (Table 1 Fig 2) The endoefect at 863 о C may be due to the appearance of a liquid phase (solidus temperature) The samples were subjected to an additional heat treatment at 800 о C for 8 h The obtained results are shown in Figs 4-6 Pattern 4 is characterized by a single Fig 1 Microscopic characterization of glass produced in the system Bi 2 crystal phase Bi 4-x which does not change on additional heat treatment The remaining two samples initially amorphous become polyphase crystalline materials upon additional thermal treatment (Bi 4-x δ-bi 2 Bi 12 SiO 20 Nd 2 Si 2 O 7 ) Fig 7 presents a UV-Vis absorption spectrum of the sample of a composition 56Bi 2 16TiO 2 8Nd2O3 (4B) Visually the sample appears red-violet of shades depending on the thickness The coloring is due to the 4f electronic transitions of Nd 3+ ions in the glass matrix [21-23] The bands characterizing these transitions in the spectrum discussed are recorded at 525 nm 583 nm and 745 nm 436

3 Stanislav Slavov Elena Kashchieva Svetlin Parvanov Yanko Dimitriev Table 1 Phase characterization of the samples of system Bi 2 Index of the sample Nominal composition Temperature time of melting 4 30Bi 2 50TiO 2 10SiO 2 10Nd o C 20 min Micro structure Glass and crystals Phase composition according to XRD Glass + Вi 4-x 4A 63Bi 2 18TiO 2 10SiO 2 9Nd o C 10 min Glass Glass 4B 56Bi 2 16TiO 2 8Nd o C 10 min Glass Glass 4C 36 Bi 2 45TiO 2 10SiO 2 9 Nd o C 10 min 4D 32 Bi 2 40TiO 2 8 Nd o C 10 min 4E 40Bi 2 50TiO 2 5SiO 2 5 Nd o C 10 min Glass and crystals Glass and crystals Crystals from the melt Glass + Вi 4-x δ-вi 2 Glass + Вi 4-x Вi 4-x δ-вi 2 Fig 2 XRD pattern of selected samples in the system Bi 2 437

4 Journal of Chemical Technology and Metallurgy Fig 3 DTA spectrum of selected samples in the system Bi 2 Fig 5 XRD pattern of sample 4A with a composition 63Bi 2 18TiO 2 10SiO 2 9Nd 2 before and after further crystallization Fig 4 XRD pattern of sample 4 with a composition 30Bi 2 50TiO 2 10SiO 2 10Nd 2 before and after further crystallization Fig 6 XRD pattern of sample 4B with a composition 56Bi 2 16TiO 2 8Nd 2 before and after further crystallization CONCLUSIONS It is shown that TiO 2 content increase changes fundamentally the phase formation in the process of cooling and in case of additional heat treatment A single-phase polycrystalline material containing Bi 4-x phase is obtained Compositions containing more than 50 mol % of Bi 2 provide to obtain vitreous samples which convert into polyphase crystalline materials upon heat treatment The glasses are of a low softening temperature (476 о C for 4A and 4B) and a crystallization temperature above 550 о C which indicates good thermal stability (ΔT = 80 о C) Participation of Nd 2 (8 mol % - 10 mol %) stabilizes the vitreous state preventing crystallization The proven good solubility and specific coloration obtained on Nd 2 introduction to glasses is a prerequisite for the creation of materials of potential use for decorative purposes art products and glasses for optic technology 438

5 Stanislav Slavov Elena Kashchieva Svetlin Parvanov Yanko Dimitriev Fig 7 XRD pattern of sample e with a composition 60Bi 2 20TiO 2 Fig 8 Uv-Vis spectrum of sample 4B with a composition 56Bi 2 16TiO 2 8Nd 2 Acknowledgements The study was performed with financial support of the University of Chemical Technology and Metallurgy Sofia under Grant 11360/2014 REFERENCES 1 EP Kashchieva MZ Krapchanska SS Slavov YB Dimitriev Effect of synthesis route on the microstructure of SiO 2 doped bismuth titanate ceramics Processing and Application of Ceramics SS Slavov MZ Krapchanska EP Kashchieva YB Dimitriev Electrical characteristics of bismuth titanate glass-ceramics containing SiO 2 and Nd 2 Processing and Application of Ceramics SS Slavov EP Kashchieva SB Parvanov YB Dimitriev Conductivity dielectric loses and dielectric permittivity depending on the temperature of bismuth titanate ceramics and glass-ceramics containing SiO 2 and Nd 2 as additives Processing and Application of Ceramics SS Slavov MZ Krapchanska EP Kashchieva SB Parvanov YB Dimitriev Electrical characteristics of bismuth titanate ceramics and glass-ceramics containing SiO 2 and Nd 2 as additives Key Engineering Materials SS Slavov EP Kashchieva SB Parvanov YB Dimitriev Sinthesis of doped bismuth titanate ceramics with Nd 2 and SiO 2 and their electrical properties Journal of Chemical Technology and Metallurgy S Kamba D Noujni A Pashkin J Petzelt R C Pullar A-K Axelsson N McN Alford Lowtemperature microwave and THz dielectric response in novel microwave ceramics J Eur Cer Soc J Takahashi T Fujii S Shimada K Kodaira Changes in ordered structure and dielectric properties with the A-site and B-site cation ratios of complex perovskites (Sr 1 x Ba x )(Sr y Ta 0 67 y ) δ J Eur Cer Soc T Bruton The growth of ``thick single crystals of Bi 4 from bisnuth borate solutions J Cryst Growth S Kojima A Hushur F Jiang S Hamazaki M Takashige M Jiang S Shimada Crystallization of amorphous bismuth titanate J Non-Cryst Sol K Gerth C Rüssel Crystallization of Bi 4 from glasses in the system Bi 2 /TiO 2 /B 2 J Non- Crys Sol T Goto Y Yamasaki H Watanabe T Kimura Y Tokura Anticorrelation between ferromagnetism and ferroelectricity in perovskite manganites Phys Rev B T Goto H Shintani K Ishizaka T Arima Y Tokura T Kimura Magnetic control of ferroelectric polarization Nature T Kimura Y Yoshida Origin of Texture 439

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