Microstructure and Electrical Properties of Mn-Ni-In Spinels

Abstract

Microstructural investigations of negative temperature coefficient (NTC) ceramics in the Mn±Ni±In±O system have been performed using X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopy (TEM). The electrical properties have been characterized by measurements of resistance, activation energy and aging. The replacement of Mn by In in Mn 2.9± ±x Ni x In 0.1 O 4 (x 0:50À0:66) leads to higher resistivities and thermal constants, both decreasing with increasing Ni content, and minimum aging of 0.1% for x 0:58. Microstructural changes deduced from the a/c ratio and caused by aging are observable for Mn 2.32 Ni 0.58 In 0.1 O 4 which is nearest to the tetragonal/cubic phase boundary. It is concluded that the Mn 3 concentration on octahedral sites increases due to aging. The domain configuration changes with increasing Ni content: samples with low Ni content reveal domain laths ($100 nm width) with internal twinning (<10 nm), samples near to the boundary exhibit finer scaled (5±10 nm), weakly curved domains without twinning and for high Ni contents a slightly increased domain width of 5±15 nm is observed. With the exception of x 0:58, all aged samples show the same microstructure as the corresponding non-aged ones, whereas aged Mn 2.32 Ni 0.58 In 0.1 O 4 is more comparable with Mn 2.40 Ni 0.50 In 0.1 O 4 . Consequently, the choice of composition with respect to the phase boundary is decisive for the electrical and microstructural behaviour.

Negative Temperature Coefficient Resistance (NTCR) Ceramic Thermistors: An Industrial Perspective

“…50,85,[93][94][95][96][97][98][99][100][101][102][103] Nevertheless, most investigators are still divided concerning the exact origin of the aging of the electrical properties of spinels; however, theories based on redistribution of charge over time are often evoked. 50,85,[93][94][95][96][97][98][99][100][101][102][103] Nevertheless, most investigators are still divided concerning the exact origin of the aging of the electrical properties of spinels; however, theories based on redistribution of charge over time are often evoked.…”

“…In 2000, Metzmacher et al 85 proposed that the large volume wall associated with a fine-scale tweed grain submicrostructure may reduce aging by ferroelastic pinning Mn 31 , inhibiting charge redistribution between tetrahedra and octahedra. The cation redistribution model to explain aging in spinels is also indirectly supported by the higher stability exhibited by perovskite-based NTCR thermistors, where A to B cation transitions are rather improbable.…”

“…More recently, some authors consider hopping between multivalent ions of different chemical species occupying octahedral positions, 50 31 to ensure an increase in the resistivity and, consequently, an increase of the B-values. 85 Oxygen partial pressure plays an important role in the concentrations of charge carriers and, consequently, electrical conductivity. This is because cooling from sintering is carried out in air, which results in the oxidation of ceramics, which in Kro¨ger-Vink notation can be written as follows:…”

Synthesis, Phase Characterization, and Properties of Chemical Solution‐Deposited Nickel Manganite Thermistor Thin Films

“…N ickel manganite spinels are commonly used in negative temperature coefficient (NTC) thermistor applications, in which a large temperature coefficient of resistance (TCR) coupled with low aging characteristics are imperative 1–9 . From the standpoint of thin films, the high TCR values of nickel manganite spinels, ≤−6.5%/K, are substantially greater than those of the amorphous silicon or vanadium oxide films currently in use for resistive bolometers 1,10–14 .…”

Investigation of Multiply Twins in Mn2.02Co0.98O4 Ceramic by Means of Transmission Electron Microscopy

“…The interfaces of these laths form twist boundaries. So, as had been discussed in a previous study, and mentioned in other studies, the domain walls (DWs) of the internal twins ( l ) belongs to the type‐I mechanical twin, meaning that the atomic arrangement of one domain is the mirror reflection of the other by the twin interface plane. These DWs of l constitute coherent twin boundaries.…”