Materials Chemistry and Physics 73 (2002) 86–92 Antiferroelectric phase transition in Pb(Mg 1/2 X 1/2 )O 3 (X = Mo and W) Ratnakar Palai a , R.N.P. Choudhary a,∗ , H.S. Tewari b a Department of Physics, Indian Institute of Technology, Kharagpur-721 302, India b School of Pure and Applied Physics, GGD University, Bilaspur, India Received 14 July 2000; received in revised form 12 March 2001; accepted 21 March 2001 Abstract Polycrystalline samples of Pb(Mg 1/2 X 1/2 )O 3 (X = Mo and W) were synthesized by a high-temperature solid-state reaction technique. Preliminary structural (X-ray diffraction) study of the compounds shows the formation of a single phase compound. Microstructural study of the compounds shows a uniform distribution of nearly spherical grains throughout the surface of the sample. Detailed studies of relative dielectric permittivity (ε r ) and loss tangent (tan δ) of the compounds both as a function of frequency (10 2 –10 4 Hz) at room temperature (30 ◦ C) and temperature (30–320 ◦ C) at 10 kHz suggest that the compounds have antiferroelectric phase transition. The activation energy of the Mo and W containing compound was found to be 0.61 and 0.72eV, respectively. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Polycrystalline; Solid-state reaction; X-ray diffraction; Relative dielectric permittivity; Activation energy 1. Introduction Since the discovery of ferroelectricity in BaTiO 3 [1], a large number of compounds of the perovskite family with a general formula YZO 3 (Y = mono, divalent cations, Z = tri, tetra, penta and hexavalent cations) have been in- vestigated in search of new ferroelectrics/antiferroelectrics. Among all the ferroelectric perovskites studied so far, Pb-based complex compounds, solid-solution or compos- ites (i.e. PbZrO 3 , Pb(ZrTi)O 3 , (PbLaLi)(ZrTi)O 3 , PbHfO 3 , etc.) have been found very useful for various applications such as transducers, hydrophones, amplifiers, dynamical and volatile memory components, sensors, etc. [2–5]. It has also been found that the desired device parameters can be obtained on suitable substitution of single or multi-elements at the Y and/or Z-sites of the Pb-based perovskite com- pounds. Formation of the compounds in the ideal perovskite structure should satisfy with charge neutrality and tolerance factor, t (below). From an extensive literature survey it is found that not much work has been done on lead tungstate (PbWO 3 ) and lead molybdate (PbMoO 3 ). This may be due to the higher electrical conductivity of W 6+ and Mo 6+ ions [6]. Bera and Choudhary [7–9] have observed that the sub- stitution of Ba 2+ , Sr 2+ , Ca 2+ , Cd 2+ , etc. at the Y-site in- creases the Curie temperature (T c ) to a maximum of 400 ◦ C for Sr 2+ doping. To examine the effects of doping at the ∗ Corresponding author. Tel.: +3222-2221-2224, ext: 4911; fax: +91-3222-2303. E-mail address: crnpfl@phy.iitkgp.ernet.in (R.N.P. Choudhary). Z-site, we propose to substitute Mg 2+ ion at this site of lead tungstate and molybdate (i.e. Pb(Mg 1/2 X 1/2 )O 3 (X = W and Mo)). Though Pb(Mg 1/2 W 1/2 )O 3 has been reported to be antiferroelectric [10,11], not a detailed investigation of the structural, microstructural, dielectric and electrical properties of Pb(Mg 1/2 X 1/2 )O 3 (X = W and Mo) has yet been reported. The tolerance factor, t, defined as [12]: t =¯ r A + r O /( √ 2( ¯ r B + r O )), where ¯ r A is the average ionic radius of the Y-site atoms, ¯ r B the average ionic radius of Z-site atoms, r O the ionic radius of O 2- , was calculated and was found to be ≈0.90 for both compounds. It clearly shows that both compounds have distorted perovskite structure. 2. Experimental methods Polycrystalline samples of Pb(Mg 1/2 Mo 1/2 )O 3 and Pb(Mg 1/2 W 1/2 )O 3 (hereafter A and B compound) were prepared by a high-temperature solid-state reaction tech- nique using AR/GR grade carbonate and oxides; MgCO 3 (99% M/S Loba Chemicals, Bombay, India), PbO (99.9% M/S BDH, England), WO 3 (99% M/S John Baker, USA) and MoO 3 (99% M/S Loba Chemicals, Bombay, India) as starting materials in a suitable stoichiometry. The ingredient carbonate and oxides were thoroughly mixed in an agate mortar for 2 h. The mixed powders were calcined at 900 and 800 ◦ C for 8h for A and B compounds, respectively. The process of grinding and calcination was repeated several times until the desired compounds were obtained. The dried calcined powder was uniaxially pressed into 0254-0584/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0254-0584(01)00369-8