M.D. Mathews

Phase transition and negative thermal expansion in A2(MoO4)3 system (A=Fe3+, Cr3+ and Al3+)

Abstract Thermal expansion behavior of A 2 (MoO 4 ) 3 compounds, where A=Fe 3+ , Cr 3+ and Al 3+ , was studied in static air in the temperature range of 298–1073 K by a thermo-dilatometer. All the compounds showed a positive thermal expansion in the beginning, followed by a phase transition and then a negative thermal expansion (NTE). They have a monoclinic unit cell at room temperature. The negative thermal expansion coefficients (NTEC) of Fe 2 (MoO 4 ) 3 , Cr 2 (MoO 4 ) 3 and Al 2 (MoO 4 ) 3 are: −14.82×10 −6 K −1 , −9.39×10 −6 K −1 and −2.83×10 −6 K −1 , respectively. It is for the first time that some of the transition metal molybdates are shown to exhibit NTE.

Simulation of lattice thermal expansion behaviour of Th1−xPuxO2 (0.0≤x≤1.0) using CeO2 as a surrogate material for PuO2

Abstract Earlier it was shown that ThO 2 and CeO 2 form almost an ideal solid solution throughout the homogeneity range. In this manuscript, we report the lattice thermal expansion behaviour of Th 1− x Ce x O 2 (0.0≤ x ≤1.0) in the temperature range from ambient to 1473 K investigated by high-temperature X-ray diffraction. The coefficient of average lattice thermal expansion ( α a ) progressively increases on going from ThO 2 to CeO 2 in Th 1− x Ce x O 2 . The typical α a values of ThO 2 , Th 0.5 Ce 0.5 O 2 and CeO 2 were found to be 9.54×10 −6 , 10.62×10 −6 and 11.58×10 −6 K −1 , respectively in the temperature range 293–1473 K. Thus the substitution of Ce 4+ at Th 4+ sites in ThO 2 has a systematic influence on the thermal expansion behaviour. These results will be useful in simulating the thermal expansion behaviour of thoria–plutonia mixed oxides.

Bulk thermal expansion studies of Th1−xCexO2 in the complete solid solution range

Abstract ThO2 and CeO2 are shown to form an almost ideal solid solution throughout the homogeneity range. Bulk thermal expansion studies on Th1−xCexO2 (0.0⩽x⩽1.0) were carried out by dilatometry from 293 to 1123 K in air. The average linear thermal expansion coefficients, α , of ThO2 and CeO2 were found to be 9.04×10−6 and 11.58×10 −6 K −1 , respectively, between 293 and 1123 K. The substitution of Ce4+ at Th4+ sites in ThO2 induced a systematic upward trend in the thermal expansion behavior throughout this series of solid solution on going from ThO2 to CeO2.

Thermal expansion of ThO2–2 wt% UO2 by HT-XRD

Abstract The linear thermal expansion of polycrystalline ThO2–2 wt% UO2 has been investigated from room temperature to 1473 K in flowing helium atmosphere using high temperature X-ray diffractometry. ThO2–2 wt% UO2 shows a marginally higher linear thermal expansion as compared to pure ThO2. The average linear and volume thermal expansion coefficients of ThO2–2 wt% UO2 are found to be α a =9.74×10 −6 K −1 and α v =29.52×10 −6 K −1 (298–1473 K). This study will be useful in designing the nuclear reactor fuel assembly based on ThO2.

Thermal expansion of LaBa2Cu2CoO7+δ

In this paper, the authors report high-temperature X-ray diffraction (HTXRD) and dilatometric studies on LaBa{sub 2}Cu{sub 2}CoO{sub 7+{delta}}. Bulk and volume thermal expansion studies, along with a study of its phase transition, were carried out. The linear and volume thermal expansion coefficients were found to be 11.7 x 10{sup {minus}6}K{sup {minus}1} and 42.3 x 10{sup {minus}6}K{sup {minus}1}, respectively.Abstract In this paper, we report high-temperature X-ray diffraction (HTXRD) and dilatometric studies on LaBa 2 Cu 2 CoO 7+δ . Bulk and volume thermal expansion studies, along with a study of its phase transition, were carried out. The linear and volume thermal expansion coefficients were found to be 11.7 × 10 −6 K −1 and 42.3 × 10 −6 K −1 , respectively.

Original ArticlesThermal expansion of LaBa2Cu2CoO7+δ

In this paper, the authors report high-temperature X-ray diffraction (HTXRD) and dilatometric studies on LaBa{sub 2}Cu{sub 2}CoO{sub 7+{delta}}. Bulk and volume thermal expansion studies, along with a study of its phase transition, were carried out. The linear and volume thermal expansion coefficients were found to be 11.7 x 10{sup {minus}6}K{sup {minus}1} and 42.3 x 10{sup {minus}6}K{sup {minus}1}, respectively.Abstract In this paper, we report high-temperature X-ray diffraction (HTXRD) and dilatometric studies on LaBa 2 Cu 2 CoO 7+δ . Bulk and volume thermal expansion studies, along with a study of its phase transition, were carried out. The linear and volume thermal expansion coefficients were found to be 11.7 × 10 −6 K −1 and 42.3 × 10 −6 K −1 , respectively.