Presentation Title

Non-cooperative Octahedral Tilting Transition of Double-Perovskites Ca2SrWO6 and Sr2.9Ca0.1WO6

Faculty Mentor

Dr. Allyson Fry-Petit

Start Date

18-11-2017 10:45 AM

End Date

18-11-2017 11:00 AM

Location

9-279

Session

Physical Sciences 1

Type of Presentation

Oral Talk

Subject Area

physical_mathematical_sciences

Abstract

Double-perovskite oxides A2B’B”O6 are derivatives of the basic perovskite structures of the form ABO3. In this experiment, the structures of two known perovskites were investigated to determine if they adopt a non-cooperative octahedral tilting (NCOT) structure. The double perovskite Ca2SrWO6 was reported to share the cooperative structure of the basic perovskite Ca3WO6 with the space group P21/n. The converged Rietveld refinement of Ca2SrWO6 suggested that the correct formula is SrCaCaWO6, indicating that Sr, due to its relatively large size, occupies the A/A' site. Attempts to lower the space group symmetry of Ca2SrWO6 from P21/n to P1 produced bond valence sum averages that closely matched the oxidation state of each atom, suggesting that the previously reported structure was not able to chemically describe the structure. Further data analysis of Ca2SrWO6 indicated that the Cc space group, which is the high-temperature NCOT structure of the Sr3WO6 compound, was a better fit than the cooperative structure of Ca3WO6. Further investigation into the ability to control the structure of NCOT compounds was explored through calcium doping of NCOT Sr3WO6. Doping of calcium of 0.033% showed that the high-temperature NCOT structure observed in Ca2SrWO6 could be induced in Sr3WO6 without the application of temperature, but instead the application of chemical pressure. The full solid solution between Sr3WO6 and Ca2SrWO6 was investigated to probe the effect of chemical pressure on NCOT compounds further. Neutron diffraction data is currently being collected to allow for a more accurate determination of the structures of Ca2SrWO6 and Sr2.9Ca0.1WO6.

10 Key Words

1) Perovskites

2) Non-Cooperative Octahedral Tilting

3) Cooperative

4) Rietveld Refinement

5) Space group symmetry

6) Solid Solution

7) Bond Valence Sum Averages

8) Oxidation States

9) High Temperature

10) Chemical Pressure

Summary of research results to be presented

The basic perovskite is a crystal structure of the form ABO3. In this experiment, two known double perovskite structures of the form A2B’B”O6 were investigated to determine if they adopt a non-cooperative octahedral tilting (NCOT) structure. The double perovskite Ca2SrWO6 was reported to have cooperative properties, but through data refinements it was determined that the NCOT properties of a high temperature Sr3WO6 was a better fit for Ca2SrWO6 structure. The NCOT properties are further investigated by adding small amounts of calcium to the high temperature Sr3WO6 and understanding how chemical pressure tempts to favor Sr3WO6 without high temperatures analysis.

This document is currently not available here.

Share

COinS
 
Nov 18th, 10:45 AM Nov 18th, 11:00 AM

Non-cooperative Octahedral Tilting Transition of Double-Perovskites Ca2SrWO6 and Sr2.9Ca0.1WO6

9-279

Double-perovskite oxides A2B’B”O6 are derivatives of the basic perovskite structures of the form ABO3. In this experiment, the structures of two known perovskites were investigated to determine if they adopt a non-cooperative octahedral tilting (NCOT) structure. The double perovskite Ca2SrWO6 was reported to share the cooperative structure of the basic perovskite Ca3WO6 with the space group P21/n. The converged Rietveld refinement of Ca2SrWO6 suggested that the correct formula is SrCaCaWO6, indicating that Sr, due to its relatively large size, occupies the A/A' site. Attempts to lower the space group symmetry of Ca2SrWO6 from P21/n to P1 produced bond valence sum averages that closely matched the oxidation state of each atom, suggesting that the previously reported structure was not able to chemically describe the structure. Further data analysis of Ca2SrWO6 indicated that the Cc space group, which is the high-temperature NCOT structure of the Sr3WO6 compound, was a better fit than the cooperative structure of Ca3WO6. Further investigation into the ability to control the structure of NCOT compounds was explored through calcium doping of NCOT Sr3WO6. Doping of calcium of 0.033% showed that the high-temperature NCOT structure observed in Ca2SrWO6 could be induced in Sr3WO6 without the application of temperature, but instead the application of chemical pressure. The full solid solution between Sr3WO6 and Ca2SrWO6 was investigated to probe the effect of chemical pressure on NCOT compounds further. Neutron diffraction data is currently being collected to allow for a more accurate determination of the structures of Ca2SrWO6 and Sr2.9Ca0.1WO6.

10 Key Words

1) Perovskites

2) Non-Cooperative Octahedral Tilting

3) Cooperative

4) Rietveld Refinement

5) Space group symmetry

6) Solid Solution

7) Bond Valence Sum Averages

8) Oxidation States

9) High Temperature

10) Chemical Pressure