WO2006095839-A1  BERTINI L ET AL: "Thermoelectric performance of large single crystal clathrate Ba8Ga16Gesub 30" THERMOELECTRICS, 2003 TWENTY-SECOND INTERNATIONAL CONFERENCE ON - ICT LA GRANDE MOTTE, FRANCE AUG. 17-21, 2003, PISCATAWAY, NJ, USA,IEEE, 17 August 2003 (2003-08-17), pages 127-130, XP010697200 ISBN: 0-7803-8301-X;  BERTINI L ET AL: "Thermoelectric performance of large single crystal clathrate Ba8Ga16Ge/sub 30" THERMOELECTRICS, 2003 TWENTY-SECOND INTERNATIONAL CONFERENCE ON - ICT LA GRANDE MOTTE, FRANCE AUG. 17-21, 2003, PISCATAWAY, NJ, USA,IEEE, 17 August 2003 (2003-08-17), pages 127-130, XP010697200 ISBN: 0-7803-8301-X;  CARRILLO-CABRERA W ET AL: "Crystal structure of Ba8Ga4.44Ge39.14-2.42, Ba8Ga8.62Ge36-1.38, and Ba8Ga12.35Ge33.27-0.38, three clathrate-I variants" ZEITSCHRIFT FUR KRISTALLOGRAPHIE - NEW CRYSTAL STRUCTURES OLDENBOURG GERMANY, vol. 217, no. 2, 2002, pages 183-185, XP002388985 ISSN: 1433-7266;  JIANJUN DONG ET AL: "Chemical trends of the rattling phonon modes in alloyed germanium clathrates" JOURNAL OF APPLIED PHYSICS AIP USA, vol. 87, no. 11, 1 June 2000 (2000-06-01), pages 7726-7734, XP002388986 ISSN: 0021-8979;  KUZNETSOV V L ET AL: "Preparation and thermoelectric properties of A8IIB16IIIB30IV clathrate compounds" JOURNAL OF APPLIED PHYSICS, AMERICAN INSTITUTE OF PHYSICS. NEW YORK, US, vol. 87, no. 11, 1 June 2000 (2000-06-01), pages 7871-7875, XP012049172 ISSN: 0021-8979;  ANNO H ET AL: "Thermoelectric properties of Ba8GaxGe46-x clathrate compounds" THERMOELECTRICS, 2002. PROCEEDINGS ICT '02. TWENTY-FIRST INTERNATIONAL CONFERENCE ON AUG. 25-29, 2002, PISCATAWAY, NJ, USA,IEEE, 25 August 2002 (2002-08-25), pages 77-80, XP010637435 ISBN: 0-7803-7683-8 cited in the application;  JUNG-HWAN KIM ET AL: "High thermoelectric performance of type-III clathrate compounds of the Ba-Ge-Ga system" ACTA MATERIALIA ELSEVIER UK, vol. 54, no. 8, May 2006 (2006-05), pages 2057-2062, XP002388987 ISSN: 1359-6454;  BRYAN J DANIEL ET AL: "Nonstoichiometry and chemical purity effects in thermoelectric Ba8Ga16Ge30 clathrate" JOURNAL OF APPLIED PHYSICS, AMERICAN INSTITUTE OF PHYSICS. NEW YORK, US, vol. 92, no. 12, 15 December 2002 (2002-12-15), pages 7281-7290, XP012056780 ISSN: 0021-8979