Thermal expansion and thermodynamic properties of gadolinium hafnate ceramics

Thermal Expansion and Thermodynamic Functions of Europium Hafnate at 298–1300 K

“…The relative thermal expansion (TE) is described by the relationship The unit cell parameter versus temperature plots for europium hafnate and gadolinium hafnate [17] are almost parallel (Fig. 4, curves 1 and 4), which is an indication to the closeness of values of derivatives da(T)/dT and relative thermal expansivities: α 298 (K -1 ) = 11.79 × 10 -6 and 11.75 × 10 -6 , respectively.…”

“…The temperature-dependent unit cell parameter of cubic europium hafnate (pyrochlore) has been determined in high-temperature X-ray diffraction experiments, and thermal expansivities have been estimated. 3), (3) borrowed from [24,25], and (4) the same for Gd 2 Hf 2 O 7 [17].…”

“…The DSCderived values [14] seem overestimates, and the values derived from drop calorimetry measurements [15] and [16] are not very consistent with each other, especially at temperatures above 1000 K. Thermal expansion parameters are an important characteristic of hightemperature ceramic materials. This work comprised DSC measurements of the Eu 2 Hf 2 O 7 molar heat capacity in the range 298-1300 K, X-ray diffraction studies of temperature-dependent unit cell parameters, and assessment of thermal expansivities in the range 298-1300 K. EXPERIMENTAL Synthesis, measurement and data processing procedures are described in detail elsewhere [17]. The chemicals used in the synthesis were europium sesquioxide (99.99 wt %), hafnia (99.99 wt %) produced by Lanhit, hydrochloric acid (35-38 wt %, specialty grade 20-4), and aqueous ammonia (25-28 wt % NH 4 OH, specialty grade) produced by Khimmed.…”

“…Temperature-dependent unit cell parameter а of pyrochlore europium hafnate (Fd3m): (1) determined in this work, (2) calculated by Eq. (3), (3) borrowed from[24,25], and (4) the same for Gd 2 Hf 2 O 7[17].…”

Thermodynamic Functions of Terbium Hafnate

“…The initial substances were terbium sesquioxide (99.99 wt %, LLC Lankhit), hafnium dioxide (99.99 wt %, LLC Lankhit), hydrochloric acid (35-38 wt %, special-purity grade 20-4, LLC Khimmed), and ammonia solution (25-28 wt % NH 4 OH, specialpurity grade, LLC Khimmed). The methods of synthesis, measurement of thermal expansion and heat capacity, and processing of results were described in detail previously [13,14]. The final annealing at 1550 K for 4 h gave Tb 1.994 Hf 2.006 O 7.003 .…”