Properties of thick film Ni0.6Co0.4FeyMn2−yO4: (0 ≤ y ≤ 0.5) NTC ceramic

doi:10.1016/j.jallcom.2008.07.022

Journal of Alloys and Compounds

Volume 475, Issues 1–2, 5 May 2009, Pages 352-355

https://doi.org/10.1016/j.jallcom.2008.07.022 Get rights and content

Abstract

Fritless thick film of NTC thermistors were prepared by screen printing Ni_0.6Co_0.4Fe_yMn_2−yO₄: (0 ≤ y ≤ 0.5) ceramic, synthesized by oxalate co-precipitation method on alumina. The composition dependent resistivities, thermistor constant were investigated for the bulk (pellet form) and thick film ceramic. Fritless thick film thermistors have room temperature resistivities only four to five times that of corresponding bulk ceramic. Both the thick film and bulk Ni_0.6Co_0.4Fe_yMn_2−yO₄: (0 ≤ y ≤ 0.5) ceramic comply with Arrhenius equation. Ni_0.6Co_0.4Fe_0.2Mn_1.8O₄ shows least room temperature resistivity and high thermistor constant. Screen printed NTC thick film thermistors Ni_0.6Co_0.4Fe_yMn_2−yO₄: (0 ≤ y ≤ 0.5) with inorganic binder can be a low cost, reliable temperature sensor in planar form.

Introduction

The continuous trend towards sophisticated thick film hybrid circuits requires low cost, highly reliable temperature sensors [1]. Thick film thermistors are expected to meet these needs due to their specific advantages of design freedom in size and shape to obtain optimum characteristics.

Thermistors with negative coefficient of resistance are composed of solid solution of 3D transition metal oxides with spinel structure [2], [3], which exhibit a large decrease in resistance as temperature increases. Under low power conditions, an NTC element can be treated as a fixed resistor whose resistance R_T varies with ambient temperature T [4]: $R_{T} = R_{A} e^{B (1 / T_{A} - 1 / T)}$ where B is the material constant, and R_A is the resistance at the nominal temperature T_A, in Kelvin. The steady state response of the thermistor element has been investigated [5]. The calibration curves and electrothermal simulation models for NTC and PTC thermistors are available [6], [7].

The composition of the ceramic of solid solution of 3D the thermistors strongly affects the distribution of cations and thus changes the physical properties [8], [9], [10]. Different technological routes are used for the synthesis of single phase, homogeneous, fine-grained ceramic. Oxalate co-precipitation method [11] can be used to produce spinel thermistor ceramics.

Screen printing is a cost-effective technology to produce planer components. In thick film technology, the target film material is mixed with a binder material, often a devitrifying glass frit and a suitable solvent to produce a printable paste. Addition of glass either leads to poor electrical properties or significantly increases the possibility of chemical interaction with the metal electrodes due to the presence of complicated phases in the thick film. In addition, glass addition can cause cracks during soldering due to different thermal expansion coefficient between glasses and ceramics. However, very few glass free materials systems have been investigated [12], [13].

In this paper we report the effect of composition on the electrical properties of fritless (glass free) thick film NTC thermistors composed of Ni_0.6Co_0.4Fe_yMn_2−yO₄: (0 ≤ y ≤ 0.5) ceramic. The properties of the bulk ceramic in pellet form is also studied for comparison. Our previous work on Ni_(1−x)Co_xMn₂O₄ (0 ≤ x ≤ 1) showed that Ni_0.6Co_0.4Mn₂O₄ had least room temperature resistivity and highest thermistors constant [14]. In this work the NiCo content was kept according to the previous results and Mn was substituted with Fe.

Section snippets

Experimental

The Ni_0.6Co_0.4Fe_yMn_2−yO₄: (0 ≤ y ≤ 0.5) was prepared by co-precipitation of the respective metal sulphates with ammonium oxalate and sintering. The required quantities of Mn₂SO₄·H₂O, CoSO₄, NiSO₄·6H₂O and FeSO₄·7H₂O were dissolved in distilled water (having total metal ion concentration 0.4 M). The solution was stirred vigorously for 1 h and to this, 0.4 M ammonium oxalate solution was added drop wise with constant stirring. The obtained precipitate was washed with distilled water and decomposed at 800

Results and discussions

The XRD pattern of the thick film Ni_0.6Co_0.4Fe_yMn_2−yO₄: (0 ≤ y ≤ 0.5) is shown in Fig. 1(a). The crystalline structure of the thick film was same as that of the bulk, therefore only the XRD of thick film is given here. The diffractogram of all the composition show single-phase cubic spinel structure. The grain sizes are in the range 0.5–0.6 μm, which are smaller than those for the samples prepared by ceramic method [2]. The variation in lattice constant with composition is given in Fig. 1(b). With

Conclusions

The thick film Ni_0.6Co_0.4Fe_yMn_2−yO₄: (0 ≤ y ≤ 0.5) has cubic spinel crystalline structure and is similar to the bulk. The compositions showed good thermistor characteristics, viz., room temperature resistivity, thermistor constant, stability factor for the temperature range of 30–180 °C. Both the thick film and bulk thermistor follow Arrhenius equation over a wide range of temperature. The resistivity, thermistor constant and activation energy depends on the composition.

The highest thermistor

Acknowledgements

The author Vijaya Puri gratefully acknowledges the award of research scientist “B” by the University Grants Commission India and UGC DRS-SAP-II.

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Properties of thick film Ni0.6Co0.4FeyMn2−yO4: (0 ≤ y ≤ 0.5) NTC ceramic

Abstract

Introduction

Section snippets

Experimental

Results and discussions

Conclusions

Acknowledgements

Sens. Actuators A

Deep Sea Res. Oceeanogr. Abstr.

Solid State Ionics

J. Eur. Ceram. Soc.

Mater. Lett.

Mater. Res. Bull.

Sensors

J. Mater. Sci., Mater. Electron.

J. Mater. Sci.

Properties of thick film Ni_0.6Co_0.4Fe_yMn_2−yO₄: (0 ≤ y ≤ 0.5) NTC ceramic