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An Investigation of the Pressure-Induced Structural Phase Transition of Nanocrystalline α-CuMoO4. CRYSTALS 2022. [DOI: 10.3390/cryst12030365] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The structural behavior of nanocrystalline α-CuMoO4 was studied at ambient temperature up to 2 GPa using in situ synchrotron X-ray powder diffraction. We found that nanocrystalline α-CuMoO4 undergoes a structural phase transition into γ-CuMoO4 at 0.5 GPa. The structural sequence is analogous to the behavior of its bulk counterpart, but the transition pressure is doubled. A coexistence of both phases was observed till 1.2 GPa. The phase transition gives rise to a change in the copper coordination from square-pyramidal to octahedral coordination. The transition involves a volume reduction of 13% indicating a first-order nature of the phase transition. This transformation was observed to be irreversible in nature. The pressure dependence of the unit-cell parameters was obtained and is discussed, and the compressibility analyzed.
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Cui X, Hu T, Wu H, Zhang J, Yang L, Zhong X, Wu X, Wang J, Li X, Yang J, Gao C. Charge Carrier Transport Behavior and Dielectric Properties of BaF 2:Tb 3+ Nanocrystals. NANOMATERIALS (BASEL, SWITZERLAND) 2020; 10:nano10010155. [PMID: 31963179 PMCID: PMC7023190 DOI: 10.3390/nano10010155] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/02/2019] [Revised: 01/09/2020] [Accepted: 01/14/2020] [Indexed: 06/10/2023]
Abstract
The charge carrier behavior and dielectric properties of BaF2:Tb3+ nanocrystals have been studied by alternating current (AC) impedance spectroscopy. The electron and ion coexist in the transport process. The F- ion's contribution to the total conduction increases with the doping concentration up to 4% and then decreases. Tb doping leads to the increase of defect quantities and a variation of charge carrier transport paths, which causes the increase of the ion diffusion coefficient and the decreases of bulk and grain boundary resistance. When the Tb-doped concentration is higher than 4%, the effect of deformation potential scattering variation on the transport property is dominant, which results in the decrease of the ion diffusion coefficient and increases of bulk and grain boundary resistance. The conduction properties of our BaF2:Tb3+ nanocrystals are compared with previous results that were found for the single crystals of rare earth-doped BaF2. Tb doping causes increases of both the quantity and the probability of carrier hopping, and it finally leads to increases of BaF2 nanocrystals' permittivity in the low frequency region.
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Affiliation(s)
- Xiaoyan Cui
- Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, National Demonstration Center for Experimental Physics Education, Jilin Normal University, Siping 136000, China; (X.C.); (H.W.); (J.Z.); (L.Y.); (X.Z.); (X.W.); (J.W.); (X.L.); (J.Y.)
| | - Tingjing Hu
- Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, National Demonstration Center for Experimental Physics Education, Jilin Normal University, Siping 136000, China; (X.C.); (H.W.); (J.Z.); (L.Y.); (X.Z.); (X.W.); (J.W.); (X.L.); (J.Y.)
| | - Huangyu Wu
- Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, National Demonstration Center for Experimental Physics Education, Jilin Normal University, Siping 136000, China; (X.C.); (H.W.); (J.Z.); (L.Y.); (X.Z.); (X.W.); (J.W.); (X.L.); (J.Y.)
| | - Junkai Zhang
- Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, National Demonstration Center for Experimental Physics Education, Jilin Normal University, Siping 136000, China; (X.C.); (H.W.); (J.Z.); (L.Y.); (X.Z.); (X.W.); (J.W.); (X.L.); (J.Y.)
| | - Lihua Yang
- Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, National Demonstration Center for Experimental Physics Education, Jilin Normal University, Siping 136000, China; (X.C.); (H.W.); (J.Z.); (L.Y.); (X.Z.); (X.W.); (J.W.); (X.L.); (J.Y.)
| | - Xin Zhong
- Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, National Demonstration Center for Experimental Physics Education, Jilin Normal University, Siping 136000, China; (X.C.); (H.W.); (J.Z.); (L.Y.); (X.Z.); (X.W.); (J.W.); (X.L.); (J.Y.)
| | - Xiaoxin Wu
- Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, National Demonstration Center for Experimental Physics Education, Jilin Normal University, Siping 136000, China; (X.C.); (H.W.); (J.Z.); (L.Y.); (X.Z.); (X.W.); (J.W.); (X.L.); (J.Y.)
| | - Jingshu Wang
- Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, National Demonstration Center for Experimental Physics Education, Jilin Normal University, Siping 136000, China; (X.C.); (H.W.); (J.Z.); (L.Y.); (X.Z.); (X.W.); (J.W.); (X.L.); (J.Y.)
| | - Xuefei Li
- Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, National Demonstration Center for Experimental Physics Education, Jilin Normal University, Siping 136000, China; (X.C.); (H.W.); (J.Z.); (L.Y.); (X.Z.); (X.W.); (J.W.); (X.L.); (J.Y.)
| | - Jinghai Yang
- Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, National Demonstration Center for Experimental Physics Education, Jilin Normal University, Siping 136000, China; (X.C.); (H.W.); (J.Z.); (L.Y.); (X.Z.); (X.W.); (J.W.); (X.L.); (J.Y.)
| | - Chunxiao Gao
- State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China;
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Absolute Luminescence Efficiency of Europium-Doped Calcium Fluoride (CaF2:Eu) Single Crystals under X-ray Excitation. CRYSTALS 2019. [DOI: 10.3390/cryst9050234] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The absolute luminescence efficiency (AE) of a calcium fluoride (CaF2:Eu) single crystal doped with europium was studied using X-ray energies met in general radiography. A CaF2:Eu single crystal with dimensions of 10 × 10 × 10 mm3 was irradiated by X-rays. The emission light photon intensity of the CaF2:Eu sample was evaluated by measuring AE within the X-ray range from 50 to 130 kV. The results of this work were compared with data obtained under similar conditions for the commercially employed medical imaging modalities, Bi4Ge3O12 and Lu2SiO5:Ce single crystals. The compatibility of the light emitted by the CaF2:Eu crystal, with the sensitivity of optical sensors, was also examined. The AE of the 10 × 10 × 10 mm3 CaF2:Eu crystal peaked in the range from 70 to 90 kV (22.22 efficiency units; E.U). The light emitted from CaF2:Eu is compatible with photocathodes, charge coupled devices (CCD), and silicon photomultipliers, which are used as radiation sensors in medical imaging systems. Considering the AE results in the examined energies, as well as the spectral compatibility with various photodetectors, a CaF2:Eu single crystal could be considered for radiographic applications, including the detection of charged particles and soft gamma rays.
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Ionic Transportation and Dielectric Properties of YF₃:Eu 3+ Nanocrystals. NANOMATERIALS 2018; 8:nano8120995. [PMID: 30513769 PMCID: PMC6315919 DOI: 10.3390/nano8120995] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/16/2018] [Revised: 11/25/2018] [Accepted: 11/29/2018] [Indexed: 11/30/2022]
Abstract
The ionic transportation and dielectric properties of YF3:Eu3+ nanocrystals are investigated by AC impedance spectroscopy. The ion diffusion coefficient and conductivity increase along with the doping concentration and reach their highest values at 4% of Eu3+. The difference of ionic radius between Eu3+ and Y3+ leads to the structural disorder and lattice strain, which deduces the increase of the ion diffusion coefficient and conductivity before 4% Eu3+ doping; then the interaction of the neighboring doping ions is dominated, which results in the difficulty of ion migration and decreases of the ion diffusion coefficient and conductivity. The strong dispersion of the permittivity in the low frequency region indicates that the charge carrier transport mechanism is the ion hopping in the system. The low-frequency hopping dispersion is affected by an interfacial polarization, which exhibits a Maxwell-Wagner relaxation process, and its loss peak shifts to higher frequency with the ionic conductivity increasing.
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Cui X, Hu T, Wang J, Zhong X, Chen Y, Zhang J, Li X, Yang J, Gao C. Effect of Tb-doped Concentration Variation on the Electrical and Dielectric Properties of CaF₂ Nanoparticles. NANOMATERIALS (BASEL, SWITZERLAND) 2018; 8:E532. [PMID: 30011931 PMCID: PMC6071059 DOI: 10.3390/nano8070532] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/29/2018] [Revised: 07/11/2018] [Accepted: 07/12/2018] [Indexed: 11/16/2022]
Abstract
Calcium fluoride (CaF₂) nanoparticles with various terbium (Tb) doping concentrations were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and alternating current (AC) impedance measurement. The original shape and structure of CaF₂ nanoparticles were retained after doping. In all the samples, the dominant charge carriers were electrons, and the F- ion transference number increased with increasing Tb concentration. The defects in the grain region considerably contributed to the electron transportation process. When the Tb concentration was less than 3%, the effect of the ionic radius variation dominated and led to the diffusion of the F- ions and facilitated electron transportation. When the Tb concentration was greater than 3%, the increasing deformation potential scattering dominated, impeding F- ion diffusion and electron transportation. The substitution of Ca2+ by Tb3+ enables the electron and ion hopping in CaF₂ nanocrystals, resulting in increased permittivity.
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Affiliation(s)
- Xiaoyan Cui
- Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, National Demonstration Center for Experimental Physics Education, Jilin Normal University, Siping 136000, China.
| | - Tingjing Hu
- Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, National Demonstration Center for Experimental Physics Education, Jilin Normal University, Siping 136000, China.
| | - Jingshu Wang
- Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, National Demonstration Center for Experimental Physics Education, Jilin Normal University, Siping 136000, China.
| | - Xin Zhong
- Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, National Demonstration Center for Experimental Physics Education, Jilin Normal University, Siping 136000, China.
| | - Yinzhu Chen
- Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, National Demonstration Center for Experimental Physics Education, Jilin Normal University, Siping 136000, China.
| | - Junkai Zhang
- Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, National Demonstration Center for Experimental Physics Education, Jilin Normal University, Siping 136000, China.
| | - Xuefei Li
- Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, National Demonstration Center for Experimental Physics Education, Jilin Normal University, Siping 136000, China.
| | - Jinghai Yang
- Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, National Demonstration Center for Experimental Physics Education, Jilin Normal University, Siping 136000, China.
| | - Chunxiao Gao
- State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China.
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