Preparing a compound comprising a combination of two crystal phases

A compound comprising a combination of a first and a second crystal phase, the first crystal phase being of the phosphomolybdic type, wherein the first crystal phase corresponds to formula (1):

• AaEbVcModPeOfHg (1)
• in which:
• A is an alkali metal;
• E is selected from the elements Te, Sb and Bi;
• the indices a, b, c, d, e, g are such that:
• 0≦a≦3, 0<b≦3, 0≦c≦3, 0<d≦13, 0<e≦2, 0≦g≦3, and f represents the number of oxygen atoms necessary to satisfy the valence and the relative atomic proportions of the elements that are present,
• and the second crystal phase corresponds to formula (2):
• ZgMohXiOj (2)
• in which:
• Z is selected from the trivalent rare earths;
• X is selected from the elements V, Ga, Fe, Bi, Ce, Ti, Sb, Mn, Zn, Te;
• the indices g, h and i are such that:
• 0<g≦3, 0≦h≦3, 0≦i≦1, and j represents the number of oxygen atoms necessary to satisfy the valence and the relative atomic proportions of the elements that are present,
• wherein Z represents lanthanum.

A compound comprising a combination of a first and a second crystal phase, the first crystal phase being of the phosphomolybdic type, wherein the first crystal phase corresponds to formula (1):

• AaEbVcModPeOfHg (1)
• in which:
• A is an alkali metal;
• E is selected from the elements Te, Sb and Bi;
• the indices a, b, c, d, e, g are such that:
• 0≦a≦3, 0<b≦3, 0≦c≦3, 0<d≦13, 0<e≦2, 0≦g≦3, and f represents the en atoms necessary to satisfy the valence and the relative atomic proportions of the elements that are present,
• and the second crystal phase corresponds to formula (2):
• ZgMohXiOj (2)
• in which:
• Z is selected from the trivalent rare earths;
• X is selected from the elements V, Ga, Fe, Bi, Ce, Ti, Sb, Mn, Zn, Te;
• the indices g, h and i are such that:
• 0<g≦3, 0≦h≦3, 0≦i≦1, and j represents the number of oxygen atoms necessary to satisfy the valence and the relative atomic proportions of the elements that are present,
• wherein X represents vanadium.

A process for the preparation of a compound comprising a combination of a first and a second crystal phase, the first crystal phase being of the phosphomolybdic type, wherein the first crystal phase corresponds to formula (1):

• AaEbVcModPeOfHg (1)
• in which:
• A is an alkali metal;
• E is selected from Te, Sb and Bi;
• the indices a, b, c, d, e, g are such that:
• 0≦a≦3, 0<b≦3, 0≦c≦3, 0<d≦13, 0<e≦2, 0≦g≦3, and f represents the number of oxygen atoms necessary to satisfy the valence and the relative atomic proportions of the elements that are present,
• and the second crystal phase corresponds to formula (2):
• ZgMohXiOj (2)
• in which:
• Z is selected from the trivalent rare earths;
• X is selected from the elements V, Ga, Fe, Bi, Ce, Ti, Sb, Mn, Zn, Te;
• the indices g, h and i are such that:
• 0<g≦3, 0≦h≦3, 0≦i≦1, and j represents the number of oxygen atoms necessary to satisfy the valence and the relative atomic proportions of the elements that are present,
• which comprises the following steps:
• synthesis of the first crystal phase in the form of a first powder;
• synthesis of the second crystal phase in the form of a second powder;
• mixing of said first and second powders by grinding
• wherein the synthesis of the first crystal phase comprises the following successive steps:
• preparation of an aqueous solution comprising phosphomolybdic acid and a compound of the element E;
• mixing of said aqueous solution with an aqueous solution comprising a salt of the element A;
• precipitation, drying and calcination of said mixture in order to obtain a solid phase;
• mixing of said solid with a toluene solution comprising a compound of vanadium;
• filtration and drying at ambient temperature.

A process, for the preparation of a compound comprising a combination of a first and a second crystal phase, the first crystal phase being of the phosphomolybdic type, wherein the first crystal phase corresponds to formula (1):

• AaEbVcModPeOfHg (1)
• in which:
• A is an alkali metal;
• E is selected from the elements Te, Sb and Bi;
• the indices a, b, c, d, e, g are such that:
• 0≦a≦3, 0<b≦3, 0≦c≦3, 0<d≦13, 0<e≦2, 0≦g≦3, and f represents the number of oxygen atoms necessary to satisfy the valence and the relative atomic proportions of the elements that are present,
• and the second crystal phase corresponds to formula (2):
• ZgMohXiOj (2)
• in which:
• Z is selected from the trivalent rare earths;
• X is selected from the elements V, Ga, Fe, Bi, Ce, Ti, Sb, Mn, Zn, Te;
• the indices g, h and i are such that:
• 0<g≦3, 0≦h≦3, 0≦i≦1, and j represents the number of oxygen atoms necessary to satisfy the valence and the relative atomic proportions of the elements that are present,
• which comprises the following steps:
• synthesis of the first crystal phase in the form of a first powder;
• synthesis of the second crystal phase in the form of a second powder;
• mixing of said first and second powders by grinding
• wherein the synthesis of the second crystal phases comprises the following successive steps:
• mixing, by grinding, of molybdenum oxide MoO3 in the solid state and an oxide of the element Z in the solid state;
• heating of said mixture to a temperature of the order of 500° C.;
• carrying out successive operations of annealing said mixture at a temperature greater than 500° C. until the end product is obtained in powder form.