Xianghong Ge

Negative thermal expansion and broad band photoluminescence in a novel material of ZrScMo2VO12.

In this paper, we present a novel material with the formula of ZrScMo2VO12 for the first time. It was demonstrated that this material exhibits not only excellent negative thermal expansion (NTE) property over a wide temperature range (at least from 150 to 823 K), but also very intense photoluminescence covering the entire visible region. Structure analysis shows that ZrScMo2VO12 has an orthorhombic structure with the space group Pbcn (No. 60) at room temperature. A phase transition from monoclinic to orthorhombic structure between 70 and 90 K is also revealed. The intense white light emission is tentatively attributed to the n- and p-type like co-doping effect which creates not only the donor- and acceptor-like states in the band gap, but also donor-acceptor pairs and even bound exciton complexes. The excellent NTE property integrated with the intense white-light emission implies a potential application of this material in light emitting diode and other photoelectric devices.

Phase Transition and Negative Thermal Expansion Property of ZrMnMo3O12

A novel material of ZrMnMo3O12 with negative thermal expansion is presented. The phase transition temperature and coefficient of thermal expansion (CTE) are investigated by temperature-dependent x-ray diffraction and Raman spectra. It is shown that ZrMnMo3O12 adopts monoclinic structure with space group P21/a (No. 14) from 298 to 358 K and transforms to orthorhombic with space group Pnma (No. 62) above 363 K. The linear CTE obtained from the results of XRD refinement is −2.80 × 10−6 K−1 from 363 to 873 K. The CTE of the bulk cylinder ceramic measured by a thermal dilatometer is −4.7 × 10−6 K−1 from 373 to 773 K approximatively.

Negative thermal expansion and photoluminescence properties in a novel material ZrScW2PO12

A novel material, ZrScW2PO12, with negative thermal expansion (NTE) behavior, at least from 138 to 1300 K, and intense photoluminescence (PL) property is first reported in this paper. Temperature dependent Raman and PL spectral studies indicate that the material holds an orthorhombic structure down to about 74 K and exhibits NTE property in the temperature range. The intense PL covering nearly the whole visible region was observed and can be deconvoluted into four bands, which present different shifts with elevation of temperature. The abundant optical property may be attributed to n- and p-type like co-doping effect and the specific structure with the abnormal thermal expansion property of the material. The integrated properties might suggest potential applications of this material in light emitting diodes and other light emitting devices.

Zero and controllable thermal expansion in

HfMgMo W x O12 with , 1.0, 1.5, 2.0, and 2.5 are developed with a simple solid state method. With increasing the content of W, solid solutions of HfMgMo W x O12 crystallize in an orthorhombic structure for and a monoclinic structure for . A near-zero thermal expansion (ZTE) is realized for HfMgMo W O12 and negative coefficients of thermal expansion (NCTE) are achieved for other compositions with different values. The ZTE and variation of NCTE are attributed to the difference in electronegativity between W and Mo and incorporation of a different amount of W, which cause variable distortion of the octahedra and softening of the MoO4 tetrahedra, and hence an enhanced NCTE in the a- and c-axis and reduced CTE in the b-axis as revealed by Raman spectroscopy and x-ray diffraction.

Near-Zero Thermal Expansion and Phase Transitions in HfMg1−xZnxMo3O12

The effects of Zn2+ incorporation on the phase formation, thermal expansion, phase transition, and vibrational properties of HfMg1−xZnxMo3O12 are investigated by XRD, dilatometry, and Raman spectroscopy. The results show that (i) single phase formation is only possible for x ≤ 0.5, otherwise, additional phases of HfMo2O8 and ZnMoO4 appear; (ii) The phase transition temperature from monoclinic to orthorhombic structure of the single phase HfMg1−xZnxMo3O12 can be well-tailored, which increases with the content of Zn2+; (iii) The incorporation of Zn2+ leads to an pronounced reduction in the positive expansion of the b-axis and an enhanced negative thermal expansion (NTE) in the c-axes, leading to a near-zero thermal expansion (ZTE) property with lower anisotropy over a wide temperature range; (iv) Replacement of Mg2+ by Zn2+ weakens the Mo–O bonds as revealed by obvious red shifts of all the Mo–O stretching modes with increasing the content of Zn2+ and improves the sintering performance of the samples which is observed by SEM. The mechanisms of the negative and near-ZTE are discussed.