Journal of Solid State Chemistry 175 (2003) 52–58 Effects of vacancy concentration on the magnetic and transport properties of (La 1x Pb x ) 1y & y MnO 3 Guerman Popov, Jacob Goldsmith, and Martha Greenblatt  Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, 610 Taylor Road, Piscataway, NJ 08854-8087, USA Received 6 January 2003; received in revised form 10 February 2003; accepted 16 February 2003 Abstract (La 1x Pb x ) 1y & y MnO 3 with x ¼ 0:0520:5 and y ¼ 0; 0.05, 0.1 (where & is a vacancy) was studied to evaluate the effects of A-site vacancies on the physical properties. In this system manganese perovskites form with tolerance factors close to 1 and low A-site cation size mismatch due to similarities in the effective ionic radii of La 3+ and Pb 2+ . Increasing vacancy concentration indicates no significant effect on the lattice parameters or volume. However, the vacancies introduce a greater A-site cation size mismatch, which leads to a lowering of the ferromagnetic and metal–insulator transition temperatures, although the transitions are not broadened with increasing vacancy content. Due to the vacancies a distribution of Mn–O–Mn angles and Mn–O distances are created, and long range order in (La 1x Pb x ) 1y & y MnO 3 appears to be determined by Mn–O–Mn angles and Mn–O distances which most distort from 1801 and are the longest, respectively, in the structure. r 2003 Elsevier Science (USA). All rights reserved. 1. Introduction Perovskite materials of general composition ABO 3 exhibit many interesting properties with important technological applications. Some of the important properties include, but are not limited to, colossal magnetoresistance (CMR), superconductivity, charge ordering, ferroelectricity, and high dielectric constant. A three-dimensional (3D) network of interconnecting octahedra BO 6 can provide optimal metal–oxygen– metal angles and distances for orbital mixing that can lead to diverse effects. While in the ideal cubic structure the metal–oxygen–metal angles are 1801, the perovskite structure can distort to various degrees depending on the sizes and nature of the constituent ions. In a typical CMR material the ferromagnetic ordering is accompanied by an insulator–metal transition. Rodriguez-Martinez and Attfield [1] showed that the optimal A-site average cation size that results in a tolerance factor close to 1 in Ln 0.7 M 0.3 MnO 3 manga- nites produces a material with the highest Curie temperature, T c : The tolerance factor (t) is a quantita- tive measure of the structural perfection of the ABO 3 perovskites: t ¼ r A þ r O ffiffi 2 p ðr A þ r O Þ ; where r A is the ionic radius of 12-coordinated A cation, r B is the ionic radius of 6-coordinated B cation, and r O is the ionic radius of oxygen. The closer the tolerance factor is to unity, the closer is the structure to the ‘‘ideal’’ cubic perovskite and the closer are the B–O–B bond angles to 1801. The average ionic radius of the A-site can be varied by the presence of different rare earths and divalent cations. However, different ions on the A-site lead to disorder, because of size mismatch, and suppression of T c [1]. The disorder can be quantitatively expressed by the variance factor, s 2 ¼ /r 2 A S  /r A S 2 ; where /r A S is the average A-site cation radius [1]. Since there are no 3+ and 2+ cations whose effective ionic radii are identical, or close to each other, A-site disorder will always exist in Ln 1x M x MnO 3 perovskite manganites. Therefore, the hypothetical highest possible T c can never be achieved. Attfield [2] studied the effect of s 2 on the properties of several perovskite systems where the A-site disorder was induced by cations of different sizes; however, there has been no investigation on how the vacancies affect s 2 and the properties. ARTICLE IN PRESS  Corresponding author. Fax: 732-445-5312. E-mail address: greenblatt@rutchem.rutgers.edu (M. Greenblatt). 0022-4596/03/$-see front matter r 2003 Elsevier Science (USA). All rights reserved. doi:10.1016/S0022-4596(03)00135-X