Publication Date

8-2015

Date of Final Oral Examination (Defense)

6-5-2015

Type of Culminating Activity

Thesis - Boise State University Access Only

Degree Title

Master of Science in Materials Science and Engineering

Department

Materials Science and Engineering

Major Advisor

Darryl P. Butt, Ph.D.

Advisor

Patrick Price, Ph.D.

Advisor

Dmitri Tenne, Ph.D.

Abstract

The thermal and chemical expansion behavior of lanthanum ferrite and divalent substitutes lanthanum ferrites (La0.9M0.1FeO3, M=Ca, Sr, Ba) was investigated. These materials were fabricated by solid state methods. Thermal expansion behavior was correlated with an antiferromagnetic to paramagnetic (Néel Temperature) and an orthorhombic to rhombohedral phase transformation in all four materials. The Néel temperatures were resolved by vibrating sample magnetometry and observed from the thermal expansion behaviors, which were measured by dilatometry and high temperature x-ray diffraction. The Néel temperatures for pure lanthanum ferrite and calcium, strontium, and barium substituted compositions were 471, 351, 465, and 466°C, consecutively. These temperatures correlated to two opposing mechanisms, a charge compensation mechanism (iron (III) from iron (IV)) and crystal structure changes due to the divalent substitutes. The orthorhombic to rhombohedral phase transformations were observed by dilatometry and high temperature x-ray diffraction. The transformation temperatures were 997, 870, 950, and 836°C. The divalent substitutes influenced the thermal expansion in both the orthorhombic and rhombohedral phase. Thermal expansion increased for all compositions from the orthorhombic and rhombohedral phase. Chemical expansion was measured by dilatometry and neutron diffraction up to 1000ºC, in air, argon, and argon-6% hydrogen. The divalent substitution influenced the amount of chemical expansion due to structural changes during the reduction of iron (IV) to iron (III).

Share

COinS