Density-functional-theory predictions of mechanical behaviour and thermal properties as well as experimental hardness of the Ga-bilayer Mo2Ga2C

Mo2Ga2C is a new MAX phase with a stacking Ga-bilayer as well as possible unusual properties. To understand this unique MAX phase structure and promote possible future applications, the structure, chemical bonding, and mechanical and thermodynamic properties of Mo2Ga2C were investigated by first-principles. Using the “bond stiffness” model, the strongest covalent bonding (1162 GPa) was formed between Mo and C atoms in Mo2Ga2C, while the weakest Ga-Ga (389 GPa) bonding was formed between two Ga-atomic layers, different from other typical MAX phases. The ratio of the bond stiffness of the weakest bond to the strongest bond (0.33) was lower than 1/2, indicating the high damage tolerance and fracture toughness of Mo2Ga2C, which was confirmed by indentation without any cracks. The high-temperature heat capacity and thermal expansion of Mo2Ga2C were calculated in the framework of quasi-harmonic approximation from 0 to 1300 K. Because of the metal-like electronic structure, the electronic excitation contribution became more significant with increasing temperature above 300 K.

DFT predictions and experimental confirmation of mechanical behaviour and thermal properties of the Ga-bilayer Mo2Ga2C

Mo2Ga2C is a new MAX phase with a stacking Ga bilayer as well as possible unusual properties. To understand this unique MAX-phase structure and promote possible future applications, the structure, chemical bonding, mechanical and thermodynamic properties of Mo2Ga2C were investigated by first principles. Using the "bond stiffness" model, the strongest covalent bonding (1162 GPa) were formed between Mo and C atoms in Mo2Ga2C, while the weakest Ga-Ga (389 GPa) bonding were formed between two Ga-atomic layers, different from other typical MAX phases. Of interest, the ratio of the bond stiffness of the weakest bond to the strongest bond (0.33) was lower than 1/2, indicating the high damage tolerance and fracture toughness of Mo2Ga2C, which was confirmed by indentation without any cracks. The high-temperature heat capacity and thermal expansion of Mo2Ga2C were calculated in the framework of quasi-harmonic approximation from 0 K to 2000 K. Because of the metal-like electronic structure, the electronic excitation contribution became more significant with increasing temperature above 300 K.

Структура и термодинамические свойства SmGaGe-=SUB=-2-=/SUB=-O-=SUB=-7-=/SUB=-

SmGaGe2O7 has been prepared by solid-phase synthesis in air at temperatures from 1273 to 1473 K using the Sm2O3, Ga2O3, and GeO2 oxides as starting materials. The structure of the studied germanate was determined by X-ray diffraction (space group P2_1 / c; a = 7.18610(9) Angstrem, b = 6.57935(8) Angstrem, c = 12.7932(2) Angstrem). Its high-temperature heat capacity has been measured by differential scanning calorimetry. The obtained experimental dependence C_p = f (T) has been used to evaluate the thermodynamic properties of the compound.

Синтез, структура и теплофизические свойства оксидов системы YVO_4-BiVO-=SUB=-4-=/SUB=-

The Y_0.4Bi_0.6VO_4 and Y_0.6Bi_0.4VO_4 solid solutions two-phase at x _Bi = 0.95, 0.90, and 0.80 have been formed by the solid-phase synthesis from the initial Y_2O_3, Bi_2O_3, and V_2O_5 oxides burned in air at a temperature of 1173 K for 200 h and their high-temperature heat capacity has been measured in the range of 350–1000 K by differential scanning calorimetry. The thermodynamic properties of the solution solutions have been calculated using the data obtained.