Reduced thermal conductivity by nanoscale intergrowths in perovskite like layered structure La2Ti2O7

Abstract

The effect of substitution and oxidation-reduction on the thermal conductivity of perovskite-like layered structure (PLS) ceramics was investigated in relation to mass contrast and non-stoichiometry. Sr (acceptor) was substituted on the A site, while Ta (donor) was substituted on the B site of La 2 Ti 2 O 7 . Substitution in PLS materials creates atomic scale disorders to accommodate the non-stoichiometry. High resolution transmission electron microscopy and X ray diffraction revealed that acceptor substitution in La 2 Ti 2 O 7 produced nanoscale intergrowths of n ¼ 5 layered phase, while donor substitution produced nanoscale intergrowths of n ¼ 3 layered phase. As a result of these nanoscale intergrowths, the thermal conductivity value reduced by as much as $20%. Pure La 2 Ti 2 O 7 has a thermal conductivity value of $1.3 W/m K which dropped to a value of $1.12 W/m K for Sr doped La 2 Ti 2 O 7 and $0.93 W/m K for Ta doped La 2 Ti 2 O 7 at 573 K. V C 2015 AIP Publishing LLC.

Thermoelectric Study of La2Ti2-xNbxO7 (0 ≤ x ≤ 0.25) Ceramics

“…The patterns are indexed to a La 2 Ti 2 O 7 monoclinic structure ceramic (space group, P2 1 ) with the lattice constant a = 7.80896(10) Å, b = 5.54608(7) Å, and c = 13.01425(22) Å, [22] consistent with those reported in the literature [14,15]. No secondary phases were detected in any of the compositions within the detection limit of the diffractometer, and the peaks were sharp, suggesting a large particle size according to the Scherrer formula [14]. The bulk and relative density of all compositions for different Nb concentrations are plotted in Fig.…”

“…Doping has generally been observed to increase grain size, resulting in a reduced grain boundary area and scattering which may enhance the conduction [25][26][27]. The highest σ (200 S/m) at 873 K for La 2 Ti 1.9 Nb 0.1 O 7 obtained in this study is higher than the maximum σ (0.5 S/m) reported in the literature for La 1.6 Sr 0.4 Ti 2 O 6.8±δ ceramic at 573 K [14]. [28,[32][33][34][35].…”

“…The study of electrical properties of lanthanum dititanate, La 2 Ti 2 O 7 (LTO) ferroelectrics started over thirty years ago [12]. LTO belongs to the perovskite-like layered structure family with a homologous series , where A = rare earth (RE) elements, B = titanium and n (= 4 in this case of LTO) is the number of octahedral units in the perovskite layers [13,14]. [12,13,16], non-linear optical and photocatalytic properties [12,13,15,16] and nds application in gas turbines at high temperature ( 1000 o C) [15].…”

“…The structure of LTO consists of discontinuous layers of corner sharing TiO 6 octahedra in the unit cell [13,14] with La occupying interstitial positions between the octahedral ( Fig. 1) [13].…”

Role of melt behavior in modifying oxidation distribution using an interface incorporated model in selective laser melting of aluminum-based material

“…It shows that the temperature contours are not symmetrical along the center of the scan direction, and the operating temperature obtained in the powder material is significantly higher compared to that produced in the as-fabricated part due to the tremendous difference in the thermo-physical properties, e.g., the absorption of the laser energy, the thermal conductivity, and the resultant heat loss rate. The heat energy has a tendency to accumulate in the powder material caused by its combination of high laser absorption and limited heat conductivity, 23,25 leading to the formation of a higher operating temperature and the subsequent melting of the powder material. However, the bulk part, with an efficient thermal-conductivity ($230 J/(mK)), considerably promotes the efficient loss of heat from the irradiated region to the ambient, resulting in a lower operating temperature obtained in the molten pool.…”