Crystallization of ZrTiO 4 Nanocrystals in Lithium-Alumino-Silicate Glass Ceramics: Anomalous Small-Angle X‑ray Scattering Investigation Vikram Singh Raghuwanshi,* ,†,‡ Christian Rü ssel, § and Armin Hoell † † Helmholtz Zentrum Berlin fü r Materialien und Energie, Hahn-Meitner Platz 1, D-14109, Berlin, Germany ‡ Humboldt-Universitä t zu Berlin, Brook-Taylor Strasse 2, D-12489, Berlin, Germany § Otto-Schott-Institut, Friedrich-Schiller-Universitä t Jena, Fraunhoferstrasse 6, D-07743, Jena, Germany ABSTRACT: We report on anomalous small-angle X-ray scattering (ASAXS) investigations of the formation and structure of nanosized ZrTiO 4 crystals in lithium-alumino- silicate (LAS) glass during heat treatment at 750 °C for different periods of time. For a sample annealed for 30 min, ASAXS measurements near the X-ray absorption edge of Ti and Zr reveal the formation of particles (ZrTiO 4 ) surrounded by a shell-like region. The sample annealed for 240 min shows the formation of two different types of particles (spherical core-shell: ZrTiO 4 and large spherical particles: LiAlSi 2 O 6 ). Additionally, ASAXS results allow quantitative determination of the average composition and volume fraction of the nanocrystals, the surrounding region (shell), and the remaining glass matrix. Data analysis reveals the formation of an alumina enriched region around ZrTiO 4 . This alumina enriched layer makes the glass network rigid and hinders further growth of ZrTiO 4 nanoparticles. For a prolonged annealing time (240 min), a new phase (LiAlSi 2 O 6 ) is formed additionally, and the (Al/Si) ratio in the shell surrounding the ZrTiO 4 crystals decreases. Moreover, the unannealed sample also shows the formation of a Ti enriched phase during cooling of the samples. The obtained quantitative information helps to understand the crystallization and growth mechanisms of ZrTiO 4 nanocrystals in LAS glass ceramics. ■ INTRODUCTION Crystal nucleation and growth control is a critical phenomenon in the development of any glass ceramic. Glass ceramics with low thermal expansion coefficients are widely used for various scientific, industrial, and daily applications. 1-3 However, nucleation agents are used to obtain homogeneously dispersed and nanograined crystals during heat treatment of the glass ceramics. 4,5 This helps to produce ultratransparent glass ceramics containing nanocrystals which make them potential candidates for applications in optical devices. 6 Therefore, it is mandatory to fully understand the nucleation, growth, and stabilization mechanisms of nanoparticles in glass ceramic systems. The present interest in the formation of ZrTiO 4 nanocrystals in glass ceramics motivates us to investigate their collective properties which are useful for both the fundamentals and the technological applications. 7,8 Lithium-alumino-silicate (LAS) transparent glass ceramics containing ZrTiO 4 and LiAlSi 2 O 6 nanoparticles are used to manufacture high temperature resistant furnace windows, cook- top panels, and telescope mirrors due to their unique property of low thermal expansion coefficients. 9,10 In these glass ceramics, the crystallization and growth of ZrTiO 4 and LiAlSi 2 O 6 crystals depend on the parent glass composition, thermal treatment, and addition of nucleation agents. 11 In earlier studies, it was reported that there is a liquid-liquid phase separation which leads to the formation of small droplets enriched in nucleation agents (Zr and Ti). 12,13 Moreover, the crystallization and growth of ZrTiO 4 nanocrystals upon heat treatment is accompanied by the formation of a diffusion barrier surrounding the precipitate. Using TEM enabled the observation of an alumina enriched layer at the interface of the ZrTiO 4 nanocrystals. This layer prevents further growth of the ZrTiO 4 nanosized crystals and suppressed Ostwald ripening. 14 The alumina enriched layer also facilitates the nucleation of a secondary LiAlSi 2 O 6 phase in the case of long time heat treatments. However, quantitative structure and composition information on nanosized crystals in the LAS glass ceramic system is still not fully revealed. Present ASAXS investigations on the studied system were performed to obtain quantitative structure and average compositions to prove the hypothesis of the crystallization and growth mechanisms of ZrTiO 4 and LiAlSi 2 O 6 nanocrystals in LAS glass ceramic systems. In this paper, the glass under study has the composition 7.6Li 2 O-0.16Na 2 O-0.13K 2 O-1.85MgO-0.33BaO-1.2ZnO- Received: January 23, 2014 Revised: March 27, 2014 Published: May 9, 2014 Article pubs.acs.org/crystal © 2014 American Chemical Society 2838 dx.doi.org/10.1021/cg5001232 | Cryst. Growth Des. 2014, 14, 2838-2845