A new member belongs to Ba2REZrO5.5 (RE = Rare-Earth) perovskites, viz. Ba2ErZrO5.5, is synthesized as nanocrystals using a combustion process. Unlike the other Ba2REZrO5.5 perovskites, which are cubic, Ba2ErZrO5.5 crystallizes in tetragonal structure having space group P4/mnc (#128). Phase purity and ultrafine morphology of Ba2ErZrO5.5 powders were examined using X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis (TGA), Fourier transform of infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) specific surface area measurements, and transmission electron microscopy (TEM). Nanocrystals of Ba2ErZrO5.5 was sintered at similar to 1500 degrees C for 4 h; whereas coarse-grained powders synthesized through solid state reaction could not be sintered even at 1700 degrees C for prolonged duration. XRD pattern of Ba2ErZrO5.5 was refined for atomic coordinates, lattice parameters, occupancies, and thermal factors using Rietveld analysis of XRD. Dielectric constant (epsilon') of Ba2ErZrO5.5 at 10 MHz is 21.62 +/- 2 and dielectric loss (tan delta) is 5 x 10(-3) at room temperature. Similar to the other Ba2REZrO5.5 perovskites, Ba2ErZrO5.5 is also showed chemically stability with YBa2Cu3O7-delta (YBCO) and Bi2Sr2Ca1Cu2Ox (Bi-2212) superconductors. Ba2ErZrO5.5 can possibly be used as a substrate for high temperature superconductor (HTS) films, or be used as an insulator in the active superconductor-insulator-superconductor (SIS) structures. (c) 2007 Elsevier Ltd. All rights reserved.