High-temperature heat capacity and heat content of CaCu3Ti4O12 (CCTO)

Dan

Phys. Chem. Chem. Phys.

et al. 2019

The binary compounds GdIr3, TbIr3 and HoIr3 are synthesized successfully and found to form in macroscopic co-existence of two polymorphic phases: C15b and AuCu3-type. The dc magnetization and heat capacity studies confirm that C15b phase orders ferromagnetically, whereas the AuCu3 phase remains paramagnetic down to 2 K. The frequency dependent ac-susceptibility data, time dependent magnetic relaxation behavior and magnetic memory effect studies suggest that TbIr3 and HoIr3 are cannonical spin-glass system, but no glassy feature could be found in GdIr3. The critical behavior of all the three compounds has been investigated from the magnetization and heat capacity measurements around the transition temperature (T C). The critical exponents α, β, γ and δ have been estimated using different techniques such as Arrott-Noaks plot, Kouvel-Fisher plot, critical isotherm as well as analysis of specific heat data and study of magnetocaloric effect. The critical analysis study identifies the type of universal magnetic class in which the three compounds belong.arXiv:1904.04807v1 [cond-mat.mtrl-sci]

Section: Heat Capacitymentioning

confidence: 99%

Physical properties of RIr₃ (R = Gd, Tb, Ho) compounds with coexisting polymorphic phases

Dan

Phys. Chem. Chem. Phys.

et al. 2019

Journal of the European Ceramic Society

“…A small amount of TÍO2 is added to metal Cu for the formation of large CuO crystals. 5 Novel materials based in the CaO-CuO-Ti0 2 system, CaCu 3 Ti 4 0i 2 (CCTO) has recently attracted much interest due to its giant dielectric constant (up to 10 5 ) which is almost frequency independent and shows good temperature stability in the range between 100 and 400 K. 6 Recently Jacob et al 7 ' 8 have determined the heat capacity of CCTO and the phase diagram for the pseudoternary system CaO-Ti0 2 -CuO/Cu 2 0 at 1000 °C as a function of oxygen partial pressure, without point to the presence of liquid phase except when the CCTO decomposed at ~1167°C in Ti0 2 , CaTi0 3 and a liquid phase rich in CU2O. Veith et al 9 have determined the phase relationship in the ternary system CuO-Ti02-CaO at 950 °C in air where the copper oxide transforms into a liquid phase during the sintering treatment and leads to anomalous grain growth.…”

Section: Introductionmentioning

confidence: 99%

Experimental determination of the eutectic temperature in air of the CuO–TiO2 pseudobinary system

Rubia

Reinosa

Leret

et al. 2012

Eutectic temperature and composition in the CuO-Ti0 2 pseudobinary system have been experimentally determined in air by means differential thermal analysis (DTA), thermogravimetry (TG) and hot-stage microscopy (HSM). Samples of the new eutectic composition treated at different temperatures have been characterized by X-ray diffraction (XRD) and X-ray absorption near-edge structural spectroscopy (XANES) to identify phases and to determine the Cu valence state, respectively. The results show that the eutectic temperature in air is higher by 100 °C (~1000 °C) for a Ti-richer composition (X Ti02 = 25 mol%) than the one calculated in the literature. The reduction of Cu 2+ to Cu + takes places at about 1030 °C. The existence of Cu 2 Ti0 3 and Cu 3 Ti0 4 has been confirmed by XRD in the temperature range between 1045 and 1200 °C.

“…In many cases [ 80 , 81 , 82 , 83 , 84 , 85 ] the predictive power of the NKR turned out to be surprisingly high, but there have also been several reports about significant deviations of calorimetric data over extended temperature ranges and even at low temperatures[ 82 , 86 , 87 ]. Grimvall [ 73 ] stated certain conditions for the inapplicability of NKR, which included the presence of anharmonic effects and significant non-vibrational contributions in either one or both of the elemental constituents.…”

Section: Results and Discussionmentioning

confidence: 99%

A Combined Experimental and First-Principles Based Assessment of Finite-Temperature Thermodynamic Properties of Intermetallic Al3Sc

et al. 2021

We present a first-principles assessment of the finite-temperature thermodynamic properties of the intermetallic Al3Sc phase including the complete spectrum of excitations and compare the theoretical findings with our dilatometric and calorimetric measurements. While significant electronic contributions to the heat capacity and thermal expansion are observed near the melting temperature, anharmonic contributions, and electron–phonon coupling effects are found to be relatively small. On the one hand, these accurate methods are used to demonstrate shortcomings of empirical predictions of phase stabilities such as the Neumann–Kopp rule. On the other hand, their combination with elasticity theory was found to provide an upper limit for the size of Al3Sc nanoprecipitates needed to maintain coherency with the host matrix. The chemo-mechanical coupling being responsible for the coherency loss of strengthening precipitates is revealed by a combination of state-of-the-art simulations and dedicated experiments. These findings can be exploited to fine-tune the microstructure of Al-Sc-based alloys to approach optimum mechanical properties.