Journal of Solid State Chemistry 167, 41–47 (2002) doi:10.1006/jssc.2002.9616 Lanthanum Gallium Tin Antimonides LaGa x Sn y Sb 2 Mark G. Morgan, Meitian Wang, Allison M. Mills, and Arthur Mar 1 Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2 Received February 1, 2000; in revised form March 28, 2002; accepted April 12, 2002 A series of quaternary lanthanum gallium tin antimonides LaGa x Sn y Sb 2 was elaborated to trace the structural evolution between the known end members LaGaSb 2 ðSmGaSb 2 -type) and LaSn y Sb 2 ðLaSn 0:75 Sb 2 -type). Five members of this series were characterized by single-crystal X-ray diffraction. For low Sn content, the Sn atoms disorder with Ga atoms in zigzag chains to form solid solutions LaGa 12y Sn y Sb 2 ð0ryr0:2Þ adopting the SmGaSb 2 -type structure, as exemplified by LaGa 0:92ð3Þ Sn 0:08 Sb 2 and LaGa 0:80ð3Þ Sn 0:20 Sb 2 ðorthorhombic, space group D 5 2  C222 1 ; Z ¼ 4Þ: For higher Sn and lower Ga content, there is a segregation in which the Sn atoms appear in chains of closely spaced partially occupied sites as in the parent LaSn 0:75 Sb 2 -type structure whereas the Ga atoms remain in zigzag chains as in the parent SmGaSb 2 -type structure. This feature is observed in the structures of LaGa 0:68ð4Þ Sn 0:31ð3Þ Sb 2 ; LaGa 0:62ð3Þ Sn 0:32ð3Þ Sb 2 ; and LaGa 0:43ð3Þ Sn 0:39ð3Þ Sb 2 ðorthorhombic, space group D 17 2h  Cmcm; Z ¼ 4Þ: The last example illustrates that the combined Ga/Sn content can be substoichiometric ðx þ yo1Þ: These compounds have a layered nature, with the chains of Ga or Sn atoms residing between 2 N ½LaSb 2  slabs. # 2002 Elsevier Science (USA) Key Words: antimonide; gallium; tin; structure. INTRODUCTION The structures of ternary rare-earth antimonides with the composition REMSb 2 can be considered as being built up by stacking 2 N ½RESb 2  slabs, followed by insertion of M atoms between these slabs (1–10). Although this partition- ing may seem somewhat artificial, it provides a connection to the structures of known rare-earth diantimonides RESb 2 (11–13). The M atoms tend to be late d-block or post- transition-metal elements, and they form networks invol- ving M–M bonding in square sheets (e.g., LaCd 0.7 Sb 2 (7)) or zigzag chains (e.g., LaIn 0.8 Sb 2 (9), REGaSb 2 (10)). There is frequently a significant substoichiometry in M, implying that the M–M bonding networks are randomly severed into finite segments. Although phase transitions in solid-state compounds, when they occur, are typically induced by temperature or pressure changes, it is also of interest to study how progressive compositional changes may cause these M–M bonding networks to distort. The similarity of the structures of LaGaSb 2 (C222 1 ) (10) and LaSn 0.75 Sb 2 (Cmcm) (8) prompted us to investigate the quaternary system LaGa x Sn y Sb 2 . The 2 N ½LaSb 2  slabs are stacked in an identical sequence in LaGaSb 2 and LaSn 0.75 Sb 2 . Running along the c-direction are zigzag chains of Ga atoms in LaGaSb 2 or slightly undulating linear chains of partially occupied Sn sites in LaSn 0.75 Sb 2 . A substantial range of nonstoichiometry occurs in La- Sn y Sb 2 , with B0:1ryrB0:7: We were interested in determining whether the transition from zigzag chains to linear chains takes place through gradual distortion of the M–M bonding network, or whether it occurs abruptly at some critical Ga/Sn ratio. Here we report the structures of five representative members in the LaGa x Sn y Sb 2 series, and demonstrate that the structural transition of the M–M bonding network proceeds through an alternative means. EXPERIMENTAL Synthesis Starting materials were La powder (99.9%, Alfa-Aesar), crushed Ga granules (99.9999%, Alfa-Aesar), Sn powder (99.8%, Cerac), and Sb powder (99.995%, Aldrich). Reactions were performed on a 0.25-g scale in evacuated fused-silica tubes (8-cm length; 10-mm i.d.). Generally, successful syntheses involved heating at temperatures between 8501C and 9501C for 2–3 days, cooling to 5001C over 1–4 days, and cooling to 201C over several hours. Products were analyzed by powder X-ray diffraction on an Enraf-Nonius FR552 Guinier camera, and elemental compositions of crystals were determined by energy- dispersive X-ray (EDX) analysis on a Hitachi S-2700 scanning electron microscope. Quaternary LaGa x Sn y Sb 2 compounds were originally identified as side products in attempts to grow single crystals of La 13 Ga 8 Sb 21 (14) and LaGaSb 2 (10) through the use of a Sn flux. Because the morphologies and 1 To whom correspondence should be addressed. Fax: 780-492-8231. E-mail: arthur.mar@ualberta.ca. 41 0022-4596/02 $35.00 r 2002 Elsevier Science (USA) All rights reserved.