The First Vatican Council (1870-71) defined Papal Infallibility as we know it today, including the concept of “ex cathedra” statements:
[quote=Vatican Council, Sess. IV, Const. de Ecclesiâ Christi, c. iv]We teach and define that it is a dogma Divinely revealed that the Roman pontiff when he speaks ex cathedra, that is when in discharge of the office of pastor and doctor of all Christians, by virtue of his supreme Apostolic authority, he defines a doctrine regarding faith or morals to be held by the universal Church, by the Divine assistance promised to him in Blessed Peter, is possessed of that infallibility with which the Divine Redeemer willed that his Church should be endowed in defining doctrine regarding faith or morals, and that therefore such definitions of the Roman pontiff are of themselves and not from the consent of the Church irreformable
Since then, there have been only** two** ex cathedra statements by popes:
The Declaration of the Immaculate Conception of Mary
Pope Pius IX as dogma in the papal bull "Ineffabilis Deus"
December 8, 1854.
[quote=Pius IX, “Ineffabilis Deus”]We declare, pronounce, and define that the doctrine which holds that the most Blessed Virgin Mary, in the first instance of her conception, by a singular grace and privilege granted by Almighty God, in view of the merits of Jesus Christ, the Savior of the human race, was preserved free from all stain of original sin, is a doctrine revealed by God and therefore to be believed firmly and constantly by all the faithful.
Hence, if anyone shall dare – which God forbid! – to think otherwise than as has been defined by us, let him know and understand that he is condemned by his own judgment; that he has suffered shipwreck in the faith; that he has separated from the unity of the Church; and that, furthermore, by his own action he incurs the penalties established by law if he should are to express in words or writing or by any other outward means the errors he think in his heart.
[font=Arial]The Declaration of the Assumption of Mary
Pope Pius XI as dogma in the papal bull "Munificentissimus Deus"
November 1, 1950
[quote=Pius XI, “Munificentissimus Deus”]…by the authority of our Lord Jesus Christ, of the Blessed Apostles Peter and Paul, and by our own authority, we pronounce, declare, and define it to be a divinely revealed dogma: that the Immaculate Mother of God, the ever Virgin Mary, having completed the course of her earthly life, was assumed body and soul into heavenly glory.
Hence if anyone, which God forbid, should dare willfully to deny or to call into doubt that which we have defined, let him know that he has fallen away completely from the divine and Catholic Faith.
[font=Arial]Hope this helps