Formation mechanism and thermoelectric properties of CaMnO3 thin films synthesized by annealing of Ca0.5Mn0.5O films

Abstract

A two-step synthesis approach was utilized to grow CaMnO 3 on M-, R-and C-plane sapphire substrates. Radio-frequency reactive magnetron sputtering was used to grow rock-salt-structured (Ca, Mn)O followed by a 3-h annealing step at 800°C in oxygen flow to form the distorted perovskite phase CaMnO 3. The effect of temperature in the post-annealing step was investigated using x-ray diffraction. The phase transformation to CaMnO 3 started at 450°C and was completed at 550°C. Films grown on R-and C-plane sapphire showed similar structure with a mixed orientation, whereas the film grown on M-plane sapphire was epitaxially grown with an out-of-plane orientation in the [202] direction. The thermoelectric characterization showed that the film grown on M-plane sapphire has about 3.5 times lower resistivity compared to the other films with a resistivity of 0.077 Xcm at 500°C. The difference in resistivity is a result from difference in crystal structure, single orientation for M-plane sapphire compared to mixed for R-and C-plane sapphire. The highest absolute Seebeck coefficient value is-350 lV K-1 for all films and is decreasing with temperature.

The effects of microstructure, Nb content and secondary Ruddlesden–Popper phase on thermoelectric properties in perovskite CaMn1−xNbxO3 (x = 0–0.10) thin films

“…The thin lms are grown by following a two-step sputtering/ annealing approach, where radio frequency (RF) reactive magnetron co-sputtering from elemental targets is used together with a post-deposition annealing step. 16,23 A 5 at% concentration of Nb resulted in a power factor of 21.6 mW K À2 m À1 at room temperature, which is the highest in this study and an 8 times increase compared to pure CaMnO 3 . This value is low compared to other studies 18,22 due to the presence of a secondary phase, identied by transmission electron microscopy (TEM) investigations as the Ruddlesden-Popper (R-P) phase.…”

“…The electrical resistivity of pure CaMnO 3 is 2.70 U cm, which is comparable to the other reported room temperature values, 1.8 U cm (ref. 16) and 8 U cm. 18 The electrical resistivity at room temperature of the Nb-alloyed samples are 0.09 U cm, 0.08 U cm, 0.18 U cm and 0.33 U cm with increasing Nb content.…”

“…The as-deposited state ((Ca,Mn)O) of CaMnO 3 thin lms is covered in detail in a previous article. 16 The addition of Nb changes the texture. XRD and TEM of the as-deposited CaMn 1Àx Nb x O 3 lms are found in the ESI.…”

“…11 Despite these advantages, oxide thermoelectrics are not widely used as they oen suffer from poor thermoelectric performance either due to high electrical resistivity or, in some cases, high thermal conductivity. [12][13][14][15][16] The thermoelectric performance of any material system is guided by the dimensionless gure of merit (ZT),…”

Structural Stability and Magnetic Ordering in BiFeO3 Perovskite Oxide: A Comparative Study GGA+U vs L(S)DA+U

“…Perovskite structure materials are of great interest in science researcher due to their specific properties and simple structure ABX 3 designated with (Pm-3m) space group where X is a non-metal and A and B span a large portion of the periodic table [1][2][3][4][5][6][7][8][9][10]. They are important in numerous high technology applications, they possess a large number of industrially important applications, including charge storage devices, Memories, Fuel Cells, capacitors, actuators, chemical reactors, energy storage, non-volatile random access memory devices, hydrogen sensors, microelectronics industry, optoelectronics sensors, piezoelectric motors wave guides, laser frequency doubling, heterogeneous catalysts, catalytic activity, atomic microscopes, ultrasound generators, , ink-jet printers and fuel injectors [11][12][13][14][15][16][17][18][19][20].…”