Electrical Properties of Magnesium Titanate Ceramics Post-Sintered by Hot Isostatic Pressing

Headnote

Abstract:

Post-sintering of magnesium titanate ceramics by hot isostatic pressing (HIP) in an oxygen-free atmosphere significantly alters various electrical properties of the product. In particular, the sintered material becomes a semiconductor. The aims of this paper are: to extend our investigations of the electrical properties of this material by expanding the frequency range of measurements, to design interpolation formulas for the frequency dependence of the complex relative permittivity, and to propose HIP-sintered magnesium titanate as a material for thermistors that have a negative-temperature-coefficient resistance (NTCR), as well as for varistors.

Keywords: Magnesium titanate; Hot isostatic pressing; Complex permittivity; Thermistors; Varistors.

Садржау Наκнадна обрада магнезцум титаната (после синтероваκа) изостатичκим пресоваκем на висощ температури, у атмосфери без κисеониκа, знача1но утиче на особине материала. Синтеровани материал поставе полупроводан. У раду наставламо истраживаκе елеκтричних особина тог материала прошириваκем фреκвенцщсκог опсега мереκа, приκазу]емо формуле за интерполаццу зависности κомплеκсне релативне пермитивности од учестаности и предлажемо примену магнезцум титаната κао материала за термисторе са негативним температурсκим сачиниоцем отпорности, κао и за варисторе.

Клучне речи: Магнезцум титанат; Изостатичκо пресоваκе при висощ температури; Комплеκсна пермитивност; Термистори; Варистори.

(ProQuest: ... denotes formulae omitted.)

1.Introduction

Magnesium titanate (MgTiO3) ceramic material has been used in electrical engineering for a long time as an insulating material [1]. Properties of the product depend on the sintering process [2, 3]. Usually, the color of the product is white and the ceramics have a moderate relative permittivity (dielectric constant) and a moderately low loss tangent. The permittivity has a positive temperature coefficient (PTC). In order to compensate the temperature variations of the permittivity, it is mixed with other materials with a negative temperature coefficient (NTC) [4]. The stabilized materials are used in electrical engineering in the production of multilayer capacitors and as carriers for various microwave devices [5].

However, if the material is sintered in air first and then post-sintered by hot isostatic pressing (HIP), the product becomes quite different: its color is dark, almost black, and it behaves as a semiconductor, exhibiting significant variations of electrical parameters as a function of frequency and temperature [2, 3]. Such a behavior can be explained by the lack of oxygen during the HIP in an inert argon atmosphere and by a high concentration of defects [3].

The present paper has several purposes....