Juan Guo

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.

A novel negative thermal expansion material of Zr0.70V1.33Mo0.67O6.73

A novel negative thermal expansion (NTE) material of Zr0.70V1.33Mo0.67O6.73 was synthesized. Its microstructure, crystal structure and thermal expansion properties were studied in detail. Structure analysis shows that Zr0.70V1.33Mo0.67O6.73 possesses a cubic crystal structure with the space group Pa (no. 205) at room temperature (RT). The experimental results show that Zr0.70V1.33Mo0.67O6.73 exhibits a stable isotropic negative thermal expansion property and maintains a cubic structure from 103 to 773 K without any phase transition. The average linear coefficients of thermal expansion (CTEs) are calculated to be −3.75 × 10−6 K−1 (163–673 K) and −4.50 × 10−6 K−1 (RT–773 K). The intrinsic linear CTEs are calculated to be −3.84 × 10−6 K−1 (103–473 K) and −4.22 × 10−6 K−1 (RT–673 K). And the phase transition temperature of ZrV2O7 has been reduced below RT, this may be attributed to the incorporation of the cubic ZrMo2O8 structure and partially occupied Zr atoms (4a). The NTE property of Zr0.70V1.33Mo0.67O6.73 can be attributed to the quasi-rigid unit modes (QRUMs).

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.