Phase Transition of Zr1-xHfxV2O7 Solid Solutions Having Negative Thermal Expansion

Abstract

⛤ǽᡡ℗ȡሱǨȚ Zr 1ࢬx Hf x V 2 O 7 ࡘΧǽᭀåᲡ ˳ʄ‫ރ‬Ȗɿ୮‫ރۑ‬౪ɿŊ ᲂɿ୮ቧᗬ˳ଉ ‫ل‬іӞᴻᲇકཪ⒈গકрগકɦɎɲȪɳȽȬȰɻɁᮾ᳣ᲇࢫ923-1292 ᮸᭔ῡలᅨ۞ 1-1 ଉ ᵹᗢগકগકрᄋᥴᢼᲇકᮾ᳣ᲇ‫ك‬કଗფࢫ305-8571 ⇹᭔dzǞǿలঙ۞ 1-1-1The phase transition of Zr 1ࢬx Hf x V 2 O 7 xࢼ0-1 solid solutions substituted for ZrIV sites was investigated using X-ray diffraction, TMA and DSC methods. X-ray diffraction experiments revealed that all compositions of Zr 1ࢬx Hf x V 2 O 7 xࢼ0-1 were of a single phase having a cubic structure. Lattice parameters of Zr 1ࢬx Hf x V 2 O 7 xࢼ0-1 at room temperature decreased linearly with increasing Hf content, due to the smaller ionic radius of the HfIV ion than that of the ZrIV ion. Abrupt positive thermal expansions in TMA were observed for all samples at two phase transition temperatures in the vicinity of T 1 ࢼ350 K and T 2 ࢼ375 K, and negative thermal expansions were seen above about 380 K. DSC measurements clearly showed that all of the Zr 1ࢬx Hf x V 2 O 7 xࢼ 0-1 samples also underwent two successive phase transitions between 330 and 390 K. Two transition temperatures and phase transition enthalpies of Zr 1ࢬx Hf x V 2 O 7 xࢼ0-1 samples decreased with the increase of x content, reflecting the decrease of superlattice structure. The sum of transition entropy for successive two phase transitions increased with increasing the normalized relative intensity of the superlattice line at room temperature.

Phonons and anomalous thermal expansion behaviour in crystalline solids

“…The temperature dependent x-ray diffraction measurements [105,180,181] for ZrV2O7 and HfV2O7 show that the phase below 350 K corresponds to a primitive 3×3×3 superstructure phase of Pa 3 space group symmetry while the high temperature phase above 375 K corresponds to the normal parent structure. The intermediate incommensurate phase is characterized by a modulation wave vector of 0.314<110> [180].…”

Experimental and Theoretical Investigation of the Elastic Properties of HfV2O7

“…DFT calculations of equilibrium lattice parameters using PBE functionals tend to overestimate experimentally determined values within 2% [35]. Moreover, given a thermal expansion coefficient of −7.2 × 10 −6 1/K [10], the calculated lattice parameter at 0 K should be decreased by 0.35% at 480 K. Second, the energetic response to deviations from equilibrium volume is significantly stronger for the static calculation than for the full relaxation case. This shape of the curves is directly related to the bulk modulus (B), representing the energetic response to uniform compression (hydrostatic pressure with uniform uniaxial strains), and is, therefore, indicating a considerably smaller B in the case of full structural relaxation at every volume.…”

“…Negative thermal expansion (NTE) phases are implemented in these composites as thermal expansion compensators [3][4][5][6]. The cubic high-temperature (HT) phase of HfV 2 O 7 (space group: Pa3, 40 atoms per cell) [6][7][8], which is stable at temperatures above~370 K [6,9], constitutes a promising candidate due to its isotropic NTE [6,7,9] with a thermal expansion coefficient of −7.2 × 10 −6 1/K [10]. Upon cooling, the HT phase transforms into an incommensurate structure between 369 K and 340 K [9].…”

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

“…15,17,21 In addition, Yamamura et al has studied the phase transition temperature of Zr 1Àx Hf x V 2 O 7 . 20 However, it's regrettable that the phase transition temperature hasn't been reduced to below room temperature successfully.…”