• Journal of Inorganic Materials
  • Vol. 36, Issue 10, 1118 (2021)
ZHU Danyang1、2, QIAN Kang1、3, CHEN Xiaopu1、2, HU Zewang1、2, LIU Xin1、2, LI Xiaoying1、2, PAN Yubai3, MIHÓKOVÁ Eva, NIKL Martin, and LI Jiang1、2、*
Author Affiliations
  • 11. Key Laboratory of Transparent Opto-functional Inorganic Materials, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 201899, China
  • 22. Center of Materials Science and Optoelectronic Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
  • 33. Department of Physics, Shanghai Normal University, Shanghai 200234, China, 4. Institute of Physics, Academy of Sciences of the Czech Republic, Prague 16200, Czech Republic
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    Abstract

    Ce:SrHfO3 ceramics possess a strong stopping power to high-energy rays due to their high density and high effective atomic number. However, it is difficult to obtain transparent Ce:SrHfO3 ceramics via traditional sintering method because of its orthogonal structure. In this work, Ce,Y:SrHfO3 ceramics were prepared by long-time vacuum sintering and short-time vacuum pre-sintering combined with hot isostatic pressing (HIP). The Ce,Y:SrHfO3 powders with a pure phase and a mean particle size of 152 nm were prepared by calcining at 1200 ℃ for 8 h using metal oxides and carbonates. The Ce,Y:SrHfO3 ceramics vacuum-sintered at 1800 ℃ for 20 h are opaque with an average grain size of 28.6 μm, while those prepared by the two-step sintering method show good optical transmittance. The evolution of the microstructure in the process of densification was analyzed in detail, and the influence of the pre-sintering temperature on the density, microstructure and optical transparency of Ce,Y:SrHfO3 ceramics was studied. The Ce,Y:SrHfO3 ceramics pre-sintered at 1500 ℃ for 2 h with HIP post-treatment at 1800 ℃ for 3 h have the highest in-line transmittance of 21.6% at 800 nm with a far smaller average grain size of 3.4 μm. Under X-ray excitation, the Ce3+ 5d-4f emission of Ce,Y:SrHfO3 ceramics was observed at 400 nm, and the XEL integral intensity is 3.3 times higher than that of Bi4Ce3O12 (BGO) crystals. The light yield of the Ce,Y:SrHfO3 ceramics is approximately 3700 ph/MeV with the shaping time of 1 μs. Good optical quality and scintillation performance of Ce,Y:SrHfO3 ceramics may expand the application range and potential in the field of scintillation detection.

    Scintillation materials are widely used in high energy physics, nuclear medicine imaging, security techniques and other X/γ ray or particle beam detection devices[1,2,3,4]. The requirements on the scintillation material performance differ in various fields, but high density, high effective atomic number, high light yield, fast scintillation decay, good time and energy resolution are generally required[5,6,7,8]. In recent years, new types of hafnate scintillators[9,10,11,12,13,14,15,16,17,18] have attracted wide attention, especially SrHfO3[19,20,21,22,23,24,25]. However, SrHfO3 is difficult to prepare in the single crystal form because of its high melting point over 2700 ℃. It was reported[26] that Ce doped SrHfO3/SrAl12O19 eutectics were prepared by the micro pulling down (μ-PD) method. Nevertheless, the size of eutectic is too small to provide practical application value. Fortunately, optical ceramic technology has gained great progress. Compared to single crystals, transparent ceramics could be obtained under suitable fabrication conditions with larger size, lower cost and more flexible composition design[27,28,29,30]. Likewise, it is relatively easy to prepare hafnate ceramics at lower temperatures. Ce:SrHfO3 ceramics have a high density (7.56  g/cm3) and effective atomic number (64), both providing rather high radiation stopping power. Ce:SrHfO3 ceramics show fast scintillation decay (21.6-42 ns) due to fast 5d-4f radiative transition of Ce3+. Excellent timing resolution (276 ps) of Ce:SrHfO3 ceramics is comparable to that of commercial high-quality LSO:Ce,Ca crystals[31]. However, the structure of SrHfO3 is orthorhombic (Pnma) at room temperature, and the birefringence effect caused by its non-cubic phase structure makes the polycrystalline ceramics difficult to be transparent. Moreover, there is a series of phase transitions during the sintering process[32]. The frequent change of the cell size hinders the densification of the ceramics. Pressure sintering (hot isostatic pressing or hot pressing) is an effective method to promote the densification of ceramics. Ce:SrHfO3 ceramics have been successfully prepared by vacuum hot pressing[22,31]. Since the graphite dies used in vacuum hot pressing causes inevitable carbon pollution, hot isostatic pressing (HIP) might prove advantageous. Hot isostatic pressing is a sintering process in which materials are subjected to balanced pressure in all directions to receive higher driving force so that the ceramics could be fully dense at lower sintering temperature with shorter time[33].

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    Danyang ZHU, Kang QIAN, Xiaopu CHEN, Zewang HU, Xin LIU, Xiaoying LI, Yubai PAN, Eva MIHÓKOVÁ, Martin NIKL, Jiang LI. Fine-grained Ce,Y:SrHfO3 Scintillation Ceramics Fabricated by Hot Isostatic Pressing [J]. Journal of Inorganic Materials, 2021, 36(10): 1118
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    Category: RESEARCH LETTER
    Received: Feb. 1, 2021
    Accepted: --
    Published Online: Nov. 26, 2021
    The Author Email: LI Jiang (lijiang@mail.sic.ac.cn)